TOMOYO Linux Cross Reference
Linux/mm/memory.c

   
   // SPDX-License-Identifier: GPL-2.0-only
   /*
    *  linux/mm/memory.c
    *
    *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
    */
   
   /*
   * demand-loading started 01.12.91 - seems it is high on the list of
   * things wanted, and it should be easy to implement. - Linus
   */
  
  /*
   * Ok, demand-loading was easy, shared pages a little bit tricker. Shared
   * pages started 02.12.91, seems to work. - Linus.
   *
   * Tested sharing by executing about 30 /bin/sh: under the old kernel it
   * would have taken more than the 6M I have free, but it worked well as
   * far as I could see.
   *
   * Also corrected some "invalidate()"s - I wasn't doing enough of them.
   */
  
  /*
   * Real VM (paging to/from disk) started 18.12.91. Much more work and
   * thought has to go into this. Oh, well..
   * 19.12.91  -  works, somewhat. Sometimes I get faults, don't know why.
   *              Found it. Everything seems to work now.
   * 20.12.91  -  Ok, making the swap-device changeable like the root.
   */
  
  /*
   * 05.04.94  -  Multi-page memory management added for v1.1.
   *              Idea by Alex Bligh (alex@cconcepts.co.uk)
   *
   * 16.07.99  -  Support of BIGMEM added by Gerhard Wichert, Siemens AG
   *              (Gerhard.Wichert@pdb.siemens.de)
   *
   * Aug/Sep 2004 Changed to four level page tables (Andi Kleen)
   */
  
  #include <linux/kernel_stat.h>
  #include <linux/mm.h>
  #include <linux/mm_inline.h>
  #include <linux/sched/mm.h>
  #include <linux/sched/coredump.h>
  #include <linux/sched/numa_balancing.h>
  #include <linux/sched/task.h>
  #include <linux/hugetlb.h>
  #include <linux/mman.h>
  #include <linux/swap.h>
  #include <linux/highmem.h>
  #include <linux/pagemap.h>
  #include <linux/memremap.h>
  #include <linux/kmsan.h>
  #include <linux/ksm.h>
  #include <linux/rmap.h>
  #include <linux/export.h>
  #include <linux/delayacct.h>
  #include <linux/init.h>
  #include <linux/pfn_t.h>
  #include <linux/writeback.h>
  #include <linux/memcontrol.h>
  #include <linux/mmu_notifier.h>
  #include <linux/swapops.h>
  #include <linux/elf.h>
  #include <linux/gfp.h>
  #include <linux/migrate.h>
  #include <linux/string.h>
  #include <linux/memory-tiers.h>
  #include <linux/debugfs.h>
  #include <linux/userfaultfd_k.h>
  #include <linux/dax.h>
  #include <linux/oom.h>
  #include <linux/numa.h>
  #include <linux/perf_event.h>
  #include <linux/ptrace.h>
  #include <linux/vmalloc.h>
  #include <linux/sched/sysctl.h>
  
  #include <trace/events/kmem.h>
  
  #include <asm/io.h>
  #include <asm/mmu_context.h>
  #include <asm/pgalloc.h>
  #include <linux/uaccess.h>
  #include <asm/tlb.h>
  #include <asm/tlbflush.h>
  
  #include "pgalloc-track.h"
  #include "internal.h"
  #include "swap.h"
  
  #if defined(LAST_CPUPID_NOT_IN_PAGE_FLAGS) && !defined(CONFIG_COMPILE_TEST)
  #warning Unfortunate NUMA and NUMA Balancing config, growing page-frame for last_cpupid.
  #endif
  
  #ifndef CONFIG_NUMA
 unsigned long max_mapnr;
 EXPORT_SYMBOL(max_mapnr);
 
 struct page *mem_map;
 EXPORT_SYMBOL(mem_map);
 #endif
 
 static vm_fault_t do_fault(struct vm_fault *vmf);
 static vm_fault_t do_anonymous_page(struct vm_fault *vmf);
 static bool vmf_pte_changed(struct vm_fault *vmf);
 
 /*
  * Return true if the original pte was a uffd-wp pte marker (so the pte was
  * wr-protected).
  */
 static __always_inline bool vmf_orig_pte_uffd_wp(struct vm_fault *vmf)
 {
         if (!userfaultfd_wp(vmf->vma))
                 return false;
         if (!(vmf->flags & FAULT_FLAG_ORIG_PTE_VALID))
                 return false;
 
         return pte_marker_uffd_wp(vmf->orig_pte);
 }
 
 /*
  * A number of key systems in x86 including ioremap() rely on the assumption
  * that high_memory defines the upper bound on direct map memory, then end
  * of ZONE_NORMAL.
  */
 void *high_memory;
 EXPORT_SYMBOL(high_memory);
 
 /*
  * Randomize the address space (stacks, mmaps, brk, etc.).
  *
  * ( When CONFIG_COMPAT_BRK=y we exclude brk from randomization,
  *   as ancient (libc5 based) binaries can segfault. )
  */
 int randomize_va_space __read_mostly =
 #ifdef CONFIG_COMPAT_BRK
                                         1;
 #else
                                         2;
 #endif
 
 #ifndef arch_wants_old_prefaulted_pte
 static inline bool arch_wants_old_prefaulted_pte(void)
 {
         /*
          * Transitioning a PTE from 'old' to 'young' can be expensive on
          * some architectures, even if it's performed in hardware. By
          * default, "false" means prefaulted entries will be 'young'.
          */
         return false;
 }
 #endif
 
 static int __init disable_randmaps(char *s)
 {
         randomize_va_space = 0;
         return 1;
 }
 __setup("norandmaps", disable_randmaps);
 
 unsigned long zero_pfn __read_mostly;
 EXPORT_SYMBOL(zero_pfn);
 
 unsigned long highest_memmap_pfn __read_mostly;
 
 /*
  * CONFIG_MMU architectures set up ZERO_PAGE in their paging_init()
  */
 static int __init init_zero_pfn(void)
 {
         zero_pfn = page_to_pfn(ZERO_PAGE(0));
         return 0;
 }
 early_initcall(init_zero_pfn);
 
 void mm_trace_rss_stat(struct mm_struct *mm, int member)
 {
         trace_rss_stat(mm, member);
 }
 
 /*
  * Note: this doesn't free the actual pages themselves. That
  * has been handled earlier when unmapping all the memory regions.
  */
 static void free_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
                            unsigned long addr)
 {
         pgtable_t token = pmd_pgtable(*pmd);
         pmd_clear(pmd);
         pte_free_tlb(tlb, token, addr);
         mm_dec_nr_ptes(tlb->mm);
 }
 
 static inline void free_pmd_range(struct mmu_gather *tlb, pud_t *pud,
                                 unsigned long addr, unsigned long end,
                                 unsigned long floor, unsigned long ceiling)
 {
         pmd_t *pmd;
         unsigned long next;
         unsigned long start;
 
         start = addr;
         pmd = pmd_offset(pud, addr);
         do {
                 next = pmd_addr_end(addr, end);
                 if (pmd_none_or_clear_bad(pmd))
                         continue;
                 free_pte_range(tlb, pmd, addr);
         } while (pmd++, addr = next, addr != end);
 
         start &= PUD_MASK;
         if (start < floor)
                 return;
         if (ceiling) {
                 ceiling &= PUD_MASK;
                 if (!ceiling)
                         return;
         }
         if (end - 1 > ceiling - 1)
                 return;
 
         pmd = pmd_offset(pud, start);
         pud_clear(pud);
         pmd_free_tlb(tlb, pmd, start);
         mm_dec_nr_pmds(tlb->mm);
 }
 
 static inline void free_pud_range(struct mmu_gather *tlb, p4d_t *p4d,
                                 unsigned long addr, unsigned long end,
                                 unsigned long floor, unsigned long ceiling)
 {
         pud_t *pud;
         unsigned long next;
         unsigned long start;
 
         start = addr;
         pud = pud_offset(p4d, addr);
         do {
                 next = pud_addr_end(addr, end);
                 if (pud_none_or_clear_bad(pud))
                         continue;
                 free_pmd_range(tlb, pud, addr, next, floor, ceiling);
         } while (pud++, addr = next, addr != end);
 
         start &= P4D_MASK;
         if (start < floor)
                 return;
         if (ceiling) {
                 ceiling &= P4D_MASK;
                 if (!ceiling)
                         return;
         }
         if (end - 1 > ceiling - 1)
                 return;
 
         pud = pud_offset(p4d, start);
         p4d_clear(p4d);
         pud_free_tlb(tlb, pud, start);
         mm_dec_nr_puds(tlb->mm);
 }
 
 static inline void free_p4d_range(struct mmu_gather *tlb, pgd_t *pgd,
                                 unsigned long addr, unsigned long end,
                                 unsigned long floor, unsigned long ceiling)
 {
         p4d_t *p4d;
         unsigned long next;
         unsigned long start;
 
         start = addr;
         p4d = p4d_offset(pgd, addr);
         do {
                 next = p4d_addr_end(addr, end);
                 if (p4d_none_or_clear_bad(p4d))
                         continue;
                 free_pud_range(tlb, p4d, addr, next, floor, ceiling);
         } while (p4d++, addr = next, addr != end);
 
         start &= PGDIR_MASK;
         if (start < floor)
                 return;
         if (ceiling) {
                 ceiling &= PGDIR_MASK;
                 if (!ceiling)
                         return;
         }
         if (end - 1 > ceiling - 1)
                 return;
 
         p4d = p4d_offset(pgd, start);
         pgd_clear(pgd);
         p4d_free_tlb(tlb, p4d, start);
 }
 
 /*
  * This function frees user-level page tables of a process.
  */
 void free_pgd_range(struct mmu_gather *tlb,
                         unsigned long addr, unsigned long end,
                         unsigned long floor, unsigned long ceiling)
 {
         pgd_t *pgd;
         unsigned long next;
 
         /*
          * The next few lines have given us lots of grief...
          *
          * Why are we testing PMD* at this top level?  Because often
          * there will be no work to do at all, and we'd prefer not to
          * go all the way down to the bottom just to discover that.
          *
          * Why all these "- 1"s?  Because 0 represents both the bottom
          * of the address space and the top of it (using -1 for the
          * top wouldn't help much: the masks would do the wrong thing).
          * The rule is that addr 0 and floor 0 refer to the bottom of
          * the address space, but end 0 and ceiling 0 refer to the top
          * Comparisons need to use "end - 1" and "ceiling - 1" (though
          * that end 0 case should be mythical).
          *
          * Wherever addr is brought up or ceiling brought down, we must
          * be careful to reject "the opposite 0" before it confuses the
          * subsequent tests.  But what about where end is brought down
          * by PMD_SIZE below? no, end can't go down to 0 there.
          *
          * Whereas we round start (addr) and ceiling down, by different
          * masks at different levels, in order to test whether a table
          * now has no other vmas using it, so can be freed, we don't
          * bother to round floor or end up - the tests don't need that.
          */
 
         addr &= PMD_MASK;
         if (addr < floor) {
                 addr += PMD_SIZE;
                 if (!addr)
                         return;
         }
         if (ceiling) {
                 ceiling &= PMD_MASK;
                 if (!ceiling)
                         return;
         }
         if (end - 1 > ceiling - 1)
                 end -= PMD_SIZE;
         if (addr > end - 1)
                 return;
         /*
          * We add page table cache pages with PAGE_SIZE,
          * (see pte_free_tlb()), flush the tlb if we need
          */
         tlb_change_page_size(tlb, PAGE_SIZE);
         pgd = pgd_offset(tlb->mm, addr);
         do {
                 next = pgd_addr_end(addr, end);
                 if (pgd_none_or_clear_bad(pgd))
                         continue;
                 free_p4d_range(tlb, pgd, addr, next, floor, ceiling);
         } while (pgd++, addr = next, addr != end);
 }
 
 void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
                    struct vm_area_struct *vma, unsigned long floor,
                    unsigned long ceiling, bool mm_wr_locked)
 {
         struct unlink_vma_file_batch vb;
 
         do {
                 unsigned long addr = vma->vm_start;
                 struct vm_area_struct *next;
 
                 /*
                  * Note: USER_PGTABLES_CEILING may be passed as ceiling and may
                  * be 0.  This will underflow and is okay.
                  */
                 next = mas_find(mas, ceiling - 1);
                 if (unlikely(xa_is_zero(next)))
                         next = NULL;
 
                 /*
                  * Hide vma from rmap and truncate_pagecache before freeing
                  * pgtables
                  */
                 if (mm_wr_locked)
                         vma_start_write(vma);
                 unlink_anon_vmas(vma);
 
                 if (is_vm_hugetlb_page(vma)) {
                         unlink_file_vma(vma);
                         hugetlb_free_pgd_range(tlb, addr, vma->vm_end,
                                 floor, next ? next->vm_start : ceiling);
                 } else {
                         unlink_file_vma_batch_init(&vb);
                         unlink_file_vma_batch_add(&vb, vma);
 
                         /*
                          * Optimization: gather nearby vmas into one call down
                          */
                         while (next && next->vm_start <= vma->vm_end + PMD_SIZE
                                && !is_vm_hugetlb_page(next)) {
                                 vma = next;
                                 next = mas_find(mas, ceiling - 1);
                                 if (unlikely(xa_is_zero(next)))
                                         next = NULL;
                                 if (mm_wr_locked)
                                         vma_start_write(vma);
                                 unlink_anon_vmas(vma);
                                 unlink_file_vma_batch_add(&vb, vma);
                         }
                         unlink_file_vma_batch_final(&vb);
                         free_pgd_range(tlb, addr, vma->vm_end,
                                 floor, next ? next->vm_start : ceiling);
                 }
                 vma = next;
         } while (vma);
 }
 
 void pmd_install(struct mm_struct *mm, pmd_t *pmd, pgtable_t *pte)
 {
         spinlock_t *ptl = pmd_lock(mm, pmd);
 
         if (likely(pmd_none(*pmd))) {   /* Has another populated it ? */
                 mm_inc_nr_ptes(mm);
                 /*
                  * Ensure all pte setup (eg. pte page lock and page clearing) are
                  * visible before the pte is made visible to other CPUs by being
                  * put into page tables.
                  *
                  * The other side of the story is the pointer chasing in the page
                  * table walking code (when walking the page table without locking;
                  * ie. most of the time). Fortunately, these data accesses consist
                  * of a chain of data-dependent loads, meaning most CPUs (alpha
                  * being the notable exception) will already guarantee loads are
                  * seen in-order. See the alpha page table accessors for the
                  * smp_rmb() barriers in page table walking code.
                  */
                 smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */
                 pmd_populate(mm, pmd, *pte);
                 *pte = NULL;
         }
         spin_unlock(ptl);
 }
 
 int __pte_alloc(struct mm_struct *mm, pmd_t *pmd)
 {
         pgtable_t new = pte_alloc_one(mm);
         if (!new)
                 return -ENOMEM;
 
         pmd_install(mm, pmd, &new);
         if (new)
                 pte_free(mm, new);
         return 0;
 }
 
 int __pte_alloc_kernel(pmd_t *pmd)
 {
         pte_t *new = pte_alloc_one_kernel(&init_mm);
         if (!new)
                 return -ENOMEM;
 
         spin_lock(&init_mm.page_table_lock);
         if (likely(pmd_none(*pmd))) {   /* Has another populated it ? */
                 smp_wmb(); /* See comment in pmd_install() */
                 pmd_populate_kernel(&init_mm, pmd, new);
                 new = NULL;
         }
         spin_unlock(&init_mm.page_table_lock);
         if (new)
                 pte_free_kernel(&init_mm, new);
         return 0;
 }
 
 static inline void init_rss_vec(int *rss)
 {
         memset(rss, 0, sizeof(int) * NR_MM_COUNTERS);
 }
 
 static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
 {
         int i;
 
         for (i = 0; i < NR_MM_COUNTERS; i++)
                 if (rss[i])
                         add_mm_counter(mm, i, rss[i]);
 }
 
 /*
  * This function is called to print an error when a bad pte
  * is found. For example, we might have a PFN-mapped pte in
  * a region that doesn't allow it.
  *
  * The calling function must still handle the error.
  */
 static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
                           pte_t pte, struct page *page)
 {
         pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
         p4d_t *p4d = p4d_offset(pgd, addr);
         pud_t *pud = pud_offset(p4d, addr);
         pmd_t *pmd = pmd_offset(pud, addr);
         struct address_space *mapping;
         pgoff_t index;
         static unsigned long resume;
         static unsigned long nr_shown;
         static unsigned long nr_unshown;
 
         /*
          * Allow a burst of 60 reports, then keep quiet for that minute;
          * or allow a steady drip of one report per second.
          */
         if (nr_shown == 60) {
                 if (time_before(jiffies, resume)) {
                         nr_unshown++;
                         return;
                 }
                 if (nr_unshown) {
                         pr_alert("BUG: Bad page map: %lu messages suppressed\n",
                                  nr_unshown);
                         nr_unshown = 0;
                 }
                 nr_shown = 0;
         }
         if (nr_shown++ == 0)
                 resume = jiffies + 60 * HZ;
 
         mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
         index = linear_page_index(vma, addr);
 
         pr_alert("BUG: Bad page map in process %s  pte:%08llx pmd:%08llx\n",
                  current->comm,
                  (long long)pte_val(pte), (long long)pmd_val(*pmd));
         if (page)
                 dump_page(page, "bad pte");
         pr_alert("addr:%px vm_flags:%08lx anon_vma:%px mapping:%px index:%lx\n",
                  (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index);
         pr_alert("file:%pD fault:%ps mmap:%ps read_folio:%ps\n",
                  vma->vm_file,
                  vma->vm_ops ? vma->vm_ops->fault : NULL,
                  vma->vm_file ? vma->vm_file->f_op->mmap : NULL,
                  mapping ? mapping->a_ops->read_folio : NULL);
         dump_stack();
         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 }
 
 /*
  * vm_normal_page -- This function gets the "struct page" associated with a pte.
  *
  * "Special" mappings do not wish to be associated with a "struct page" (either
  * it doesn't exist, or it exists but they don't want to touch it). In this
  * case, NULL is returned here. "Normal" mappings do have a struct page.
  *
  * There are 2 broad cases. Firstly, an architecture may define a pte_special()
  * pte bit, in which case this function is trivial. Secondly, an architecture
  * may not have a spare pte bit, which requires a more complicated scheme,
  * described below.
  *
  * A raw VM_PFNMAP mapping (ie. one that is not COWed) is always considered a
  * special mapping (even if there are underlying and valid "struct pages").
  * COWed pages of a VM_PFNMAP are always normal.
  *
  * The way we recognize COWed pages within VM_PFNMAP mappings is through the
  * rules set up by "remap_pfn_range()": the vma will have the VM_PFNMAP bit
  * set, and the vm_pgoff will point to the first PFN mapped: thus every special
  * mapping will always honor the rule
  *
  *      pfn_of_page == vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT)
  *
  * And for normal mappings this is false.
  *
  * This restricts such mappings to be a linear translation from virtual address
  * to pfn. To get around this restriction, we allow arbitrary mappings so long
  * as the vma is not a COW mapping; in that case, we know that all ptes are
  * special (because none can have been COWed).
  *
  *
  * In order to support COW of arbitrary special mappings, we have VM_MIXEDMAP.
  *
  * VM_MIXEDMAP mappings can likewise contain memory with or without "struct
  * page" backing, however the difference is that _all_ pages with a struct
  * page (that is, those where pfn_valid is true) are refcounted and considered
  * normal pages by the VM. The only exception are zeropages, which are
  * *never* refcounted.
  *
  * The disadvantage is that pages are refcounted (which can be slower and
  * simply not an option for some PFNMAP users). The advantage is that we
  * don't have to follow the strict linearity rule of PFNMAP mappings in
  * order to support COWable mappings.
  *
  */
 struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
                             pte_t pte)
 {
         unsigned long pfn = pte_pfn(pte);
 
         if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
                 if (likely(!pte_special(pte)))
                         goto check_pfn;
                 if (vma->vm_ops && vma->vm_ops->find_special_page)
                         return vma->vm_ops->find_special_page(vma, addr);
                 if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
                         return NULL;
                 if (is_zero_pfn(pfn))
                         return NULL;
                 if (pte_devmap(pte))
                 /*
                  * NOTE: New users of ZONE_DEVICE will not set pte_devmap()
                  * and will have refcounts incremented on their struct pages
                  * when they are inserted into PTEs, thus they are safe to
                  * return here. Legacy ZONE_DEVICE pages that set pte_devmap()
                  * do not have refcounts. Example of legacy ZONE_DEVICE is
                  * MEMORY_DEVICE_FS_DAX type in pmem or virtio_fs drivers.
                  */
                         return NULL;
 
                 print_bad_pte(vma, addr, pte, NULL);
                 return NULL;
         }
 
         /* !CONFIG_ARCH_HAS_PTE_SPECIAL case follows: */
 
         if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
                 if (vma->vm_flags & VM_MIXEDMAP) {
                         if (!pfn_valid(pfn))
                                 return NULL;
                         if (is_zero_pfn(pfn))
                                 return NULL;
                         goto out;
                 } else {
                         unsigned long off;
                         off = (addr - vma->vm_start) >> PAGE_SHIFT;
                         if (pfn == vma->vm_pgoff + off)
                                 return NULL;
                         if (!is_cow_mapping(vma->vm_flags))
                                 return NULL;
                 }
         }
 
         if (is_zero_pfn(pfn))
                 return NULL;
 
 check_pfn:
         if (unlikely(pfn > highest_memmap_pfn)) {
                 print_bad_pte(vma, addr, pte, NULL);
                 return NULL;
         }
 
         /*
          * NOTE! We still have PageReserved() pages in the page tables.
          * eg. VDSO mappings can cause them to exist.
          */
 out:
         VM_WARN_ON_ONCE(is_zero_pfn(pfn));
         return pfn_to_page(pfn);
 }
 
 struct folio *vm_normal_folio(struct vm_area_struct *vma, unsigned long addr,
                             pte_t pte)
 {
         struct page *page = vm_normal_page(vma, addr, pte);
 
         if (page)
                 return page_folio(page);
         return NULL;
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
                                 pmd_t pmd)
 {
         unsigned long pfn = pmd_pfn(pmd);
 
         /*
          * There is no pmd_special() but there may be special pmds, e.g.
          * in a direct-access (dax) mapping, so let's just replicate the
          * !CONFIG_ARCH_HAS_PTE_SPECIAL case from vm_normal_page() here.
          */
         if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
                 if (vma->vm_flags & VM_MIXEDMAP) {
                         if (!pfn_valid(pfn))
                                 return NULL;
                         goto out;
                 } else {
                         unsigned long off;
                         off = (addr - vma->vm_start) >> PAGE_SHIFT;
                         if (pfn == vma->vm_pgoff + off)
                                 return NULL;
                         if (!is_cow_mapping(vma->vm_flags))
                                 return NULL;
                 }
         }
 
         if (pmd_devmap(pmd))
                 return NULL;
         if (is_huge_zero_pmd(pmd))
                 return NULL;
         if (unlikely(pfn > highest_memmap_pfn))
                 return NULL;
 
         /*
          * NOTE! We still have PageReserved() pages in the page tables.
          * eg. VDSO mappings can cause them to exist.
          */
 out:
         return pfn_to_page(pfn);
 }
 
 struct folio *vm_normal_folio_pmd(struct vm_area_struct *vma,
                                   unsigned long addr, pmd_t pmd)
 {
         struct page *page = vm_normal_page_pmd(vma, addr, pmd);
 
         if (page)
                 return page_folio(page);
         return NULL;
 }
 #endif
 
 static void restore_exclusive_pte(struct vm_area_struct *vma,
                                   struct page *page, unsigned long address,
                                   pte_t *ptep)
 {
         struct folio *folio = page_folio(page);
         pte_t orig_pte;
         pte_t pte;
         swp_entry_t entry;
 
         orig_pte = ptep_get(ptep);
         pte = pte_mkold(mk_pte(page, READ_ONCE(vma->vm_page_prot)));
         if (pte_swp_soft_dirty(orig_pte))
                 pte = pte_mksoft_dirty(pte);
 
         entry = pte_to_swp_entry(orig_pte);
         if (pte_swp_uffd_wp(orig_pte))
                 pte = pte_mkuffd_wp(pte);
         else if (is_writable_device_exclusive_entry(entry))
                 pte = maybe_mkwrite(pte_mkdirty(pte), vma);
 
         VM_BUG_ON_FOLIO(pte_write(pte) && (!folio_test_anon(folio) &&
                                            PageAnonExclusive(page)), folio);
 
         /*
          * No need to take a page reference as one was already
          * created when the swap entry was made.
          */
         if (folio_test_anon(folio))
                 folio_add_anon_rmap_pte(folio, page, vma, address, RMAP_NONE);
         else
                 /*
                  * Currently device exclusive access only supports anonymous
                  * memory so the entry shouldn't point to a filebacked page.
                  */
                 WARN_ON_ONCE(1);
 
         set_pte_at(vma->vm_mm, address, ptep, pte);
 
         /*
          * No need to invalidate - it was non-present before. However
          * secondary CPUs may have mappings that need invalidating.
          */
         update_mmu_cache(vma, address, ptep);
 }
 
 /*
  * Tries to restore an exclusive pte if the page lock can be acquired without
  * sleeping.
  */
 static int
 try_restore_exclusive_pte(pte_t *src_pte, struct vm_area_struct *vma,
                         unsigned long addr)
 {
         swp_entry_t entry = pte_to_swp_entry(ptep_get(src_pte));
         struct page *page = pfn_swap_entry_to_page(entry);
 
         if (trylock_page(page)) {
                 restore_exclusive_pte(vma, page, addr, src_pte);
                 unlock_page(page);
                 return 0;
         }
 
         return -EBUSY;
 }
 
 /*
  * copy one vm_area from one task to the other. Assumes the page tables
  * already present in the new task to be cleared in the whole range
  * covered by this vma.
  */
 
 static unsigned long
 copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
                 pte_t *dst_pte, pte_t *src_pte, struct vm_area_struct *dst_vma,
                 struct vm_area_struct *src_vma, unsigned long addr, int *rss)
 {
         unsigned long vm_flags = dst_vma->vm_flags;
         pte_t orig_pte = ptep_get(src_pte);
         pte_t pte = orig_pte;
         struct folio *folio;
         struct page *page;
         swp_entry_t entry = pte_to_swp_entry(orig_pte);
 
         if (likely(!non_swap_entry(entry))) {
                 if (swap_duplicate(entry) < 0)
                         return -EIO;
 
                 /* make sure dst_mm is on swapoff's mmlist. */
                 if (unlikely(list_empty(&dst_mm->mmlist))) {
                         spin_lock(&mmlist_lock);
                         if (list_empty(&dst_mm->mmlist))
                                 list_add(&dst_mm->mmlist,
                                                 &src_mm->mmlist);
                         spin_unlock(&mmlist_lock);
                 }
                 /* Mark the swap entry as shared. */
                 if (pte_swp_exclusive(orig_pte)) {
                         pte = pte_swp_clear_exclusive(orig_pte);
                         set_pte_at(src_mm, addr, src_pte, pte);
                 }
                 rss[MM_SWAPENTS]++;
         } else if (is_migration_entry(entry)) {
                 folio = pfn_swap_entry_folio(entry);
 
                 rss[mm_counter(folio)]++;
 
                 if (!is_readable_migration_entry(entry) &&
                                 is_cow_mapping(vm_flags)) {
                         /*
                          * COW mappings require pages in both parent and child
                          * to be set to read. A previously exclusive entry is
                          * now shared.
                          */
                         entry = make_readable_migration_entry(
                                                         swp_offset(entry));
                         pte = swp_entry_to_pte(entry);
                         if (pte_swp_soft_dirty(orig_pte))
                                 pte = pte_swp_mksoft_dirty(pte);
                         if (pte_swp_uffd_wp(orig_pte))
                                 pte = pte_swp_mkuffd_wp(pte);
                         set_pte_at(src_mm, addr, src_pte, pte);
                 }
         } else if (is_device_private_entry(entry)) {
                 page = pfn_swap_entry_to_page(entry);
                 folio = page_folio(page);
 
                 /*
                  * Update rss count even for unaddressable pages, as
                  * they should treated just like normal pages in this
                  * respect.
                  *
                  * We will likely want to have some new rss counters
                  * for unaddressable pages, at some point. But for now
                  * keep things as they are.
                  */
                 folio_get(folio);
                 rss[mm_counter(folio)]++;
                 /* Cannot fail as these pages cannot get pinned. */
                 folio_try_dup_anon_rmap_pte(folio, page, src_vma);
 
                 /*
                  * We do not preserve soft-dirty information, because so
                  * far, checkpoint/restore is the only feature that
                  * requires that. And checkpoint/restore does not work
                  * when a device driver is involved (you cannot easily
                  * save and restore device driver state).
                  */
                 if (is_writable_device_private_entry(entry) &&
                     is_cow_mapping(vm_flags)) {
                         entry = make_readable_device_private_entry(
                                                         swp_offset(entry));
                         pte = swp_entry_to_pte(entry);
                         if (pte_swp_uffd_wp(orig_pte))
                                 pte = pte_swp_mkuffd_wp(pte);
                         set_pte_at(src_mm, addr, src_pte, pte);
                 }
         } else if (is_device_exclusive_entry(entry)) {
                 /*
                  * Make device exclusive entries present by restoring the
                  * original entry then copying as for a present pte. Device
                  * exclusive entries currently only support private writable
                  * (ie. COW) mappings.
                  */
                 VM_BUG_ON(!is_cow_mapping(src_vma->vm_flags));
                 if (try_restore_exclusive_pte(src_pte, src_vma, addr))
                         return -EBUSY;
                 return -ENOENT;
         } else if (is_pte_marker_entry(entry)) {
                 pte_marker marker = copy_pte_marker(entry, dst_vma);
 
                 if (marker)
                         set_pte_at(dst_mm, addr, dst_pte,
                                    make_pte_marker(marker));
                 return 0;
         }
         if (!userfaultfd_wp(dst_vma))
                 pte = pte_swp_clear_uffd_wp(pte);
         set_pte_at(dst_mm, addr, dst_pte, pte);
         return 0;
 }
 
 /*
  * Copy a present and normal page.
  *
  * NOTE! The usual case is that this isn't required;
  * instead, the caller can just increase the page refcount
  * and re-use the pte the traditional way.
  *
  * And if we need a pre-allocated page but don't yet have
  * one, return a negative error to let the preallocation
  * code know so that it can do so outside the page table
  * lock.
  */
 static inline int
 copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
                   pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,
                   struct folio **prealloc, struct page *page)
 {
         struct folio *new_folio;
         pte_t pte;
 
         new_folio = *prealloc;
         if (!new_folio)
                 return -EAGAIN;
 
         /*
          * We have a prealloc page, all good!  Take it
          * over and copy the page & arm it.
          */
         *prealloc = NULL;
         copy_user_highpage(&new_folio->page, page, addr, src_vma);
         __folio_mark_uptodate(new_folio);
         folio_add_new_anon_rmap(new_folio, dst_vma, addr, RMAP_EXCLUSIVE);
         folio_add_lru_vma(new_folio, dst_vma);
         rss[MM_ANONPAGES]++;
 
         /* All done, just insert the new page copy in the child */
         pte = mk_pte(&new_folio->page, dst_vma->vm_page_prot);
         pte = maybe_mkwrite(pte_mkdirty(pte), dst_vma);
         if (userfaultfd_pte_wp(dst_vma, ptep_get(src_pte)))
                 /* Uffd-wp needs to be delivered to dest pte as well */
                 pte = pte_mkuffd_wp(pte);
         set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte);
         return 0;
 }
 
 static __always_inline void __copy_present_ptes(struct vm_area_struct *dst_vma,
                 struct vm_area_struct *src_vma, pte_t *dst_pte, pte_t *src_pte,
                 pte_t pte, unsigned long addr, int nr)
 {
         struct mm_struct *src_mm = src_vma->vm_mm;
 
         /* If it's a COW mapping, write protect it both processes. */
         if (is_cow_mapping(src_vma->vm_flags) && pte_write(pte)) {
                 wrprotect_ptes(src_mm, addr, src_pte, nr);
                 pte = pte_wrprotect(pte);
         }
 
         /* If it's a shared mapping, mark it clean in the child. */
         if (src_vma->vm_flags & VM_SHARED)
                 pte = pte_mkclean(pte);
         pte = pte_mkold(pte);
 
         if (!userfaultfd_wp(dst_vma))
                 pte = pte_clear_uffd_wp(pte);
 
         set_ptes(dst_vma->vm_mm, addr, dst_pte, pte, nr);
 }
 
 /*
  * Copy one present PTE, trying to batch-process subsequent PTEs that map
  * consecutive pages of the same folio by copying them as well.
  *
  * Returns -EAGAIN if one preallocated page is required to copy the next PTE.
  * Otherwise, returns the number of copied PTEs (at least 1).
  */
 static inline int
 copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
                  pte_t *dst_pte, pte_t *src_pte, pte_t pte, unsigned long addr,
                  int max_nr, int *rss, struct folio **prealloc)
 {
         struct page *page;
         struct folio *folio;
         bool any_writable;
         fpb_t flags = 0;
         int err, nr;
 
         page = vm_normal_page(src_vma, addr, pte);
         if (unlikely(!page))
                 goto copy_pte;
 
         folio = page_folio(page);
 
         /*
          * If we likely have to copy, just don't bother with batching. Make
          * sure that the common "small folio" case is as fast as possible
          * by keeping the batching logic separate.
          */
         if (unlikely(!*prealloc && folio_test_large(folio) && max_nr != 1)) {
                 if (src_vma->vm_flags & VM_SHARED)
                         flags |= FPB_IGNORE_DIRTY;
                 if (!vma_soft_dirty_enabled(src_vma))
                         flags |= FPB_IGNORE_SOFT_DIRTY;
 
                 nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr, flags,
                                      &any_writable, NULL, NULL);
                 folio_ref_add(folio, nr);
                 if (folio_test_anon(folio)) {
                         if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page,
                                                                   nr, src_vma))) {
                                 folio_ref_sub(folio, nr);
                                 return -EAGAIN;
                         }
                         rss[MM_ANONPAGES] += nr;
                         VM_WARN_ON_FOLIO(PageAnonExclusive(page), folio);
                 } else {
                         folio_dup_file_rmap_ptes(folio, page, nr);
                         rss[mm_counter_file(folio)] += nr;
                 }
                 if (any_writable)
                         pte = pte_mkwrite(pte, src_vma);
                 __copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte,
                                     addr, nr);
                 return nr;
         }
 
         folio_get(folio);
         if (folio_test_anon(folio)) {
                 /*
                  * If this page may have been pinned by the parent process,
                  * copy the page immediately for the child so that we'll always
                  * guarantee the pinned page won't be randomly replaced in the
                  * future.
                  */
                 if (unlikely(folio_try_dup_anon_rmap_pte(folio, page, src_vma))) {
                         /* Page may be pinned, we have to copy. */
                         folio_put(folio);
                         err = copy_present_page(dst_vma, src_vma, dst_pte, src_pte,
                                                 addr, rss, prealloc, page);
                         return err ? err : 1;
                 }
                 rss[MM_ANONPAGES]++;
                 VM_WARN_ON_FOLIO(PageAnonExclusive(page), folio);
         } else {
                 folio_dup_file_rmap_pte(folio, page);
                 rss[mm_counter_file(folio)]++;
         }
 
 copy_pte:
         __copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte, addr, 1);
         return 1;
 }
 
 static inline struct folio *folio_prealloc(struct mm_struct *src_mm,
                 struct vm_area_struct *vma, unsigned long addr, bool need_zero)
 {
         struct folio *new_folio;
 
         if (need_zero)
                 new_folio = vma_alloc_zeroed_movable_folio(vma, addr);
         else
                 new_folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma,
                                             addr, false);
 
         if (!new_folio)
                 return NULL;
 
         if (mem_cgroup_charge(new_folio, src_mm, GFP_KERNEL)) {
                 folio_put(new_folio);
                 return NULL;
         }
         folio_throttle_swaprate(new_folio, GFP_KERNEL);
 
         return new_folio;
 }
 
 static int
 copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
                pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
                unsigned long end)
 {
         struct mm_struct *dst_mm = dst_vma->vm_mm;
         struct mm_struct *src_mm = src_vma->vm_mm;
         pte_t *orig_src_pte, *orig_dst_pte;
         pte_t *src_pte, *dst_pte;
         pte_t ptent;
         spinlock_t *src_ptl, *dst_ptl;
         int progress, max_nr, ret = 0;
         int rss[NR_MM_COUNTERS];
         swp_entry_t entry = (swp_entry_t){0};
         struct folio *prealloc = NULL;
         int nr;
 
 again:
         progress = 0;
         init_rss_vec(rss);
 
         /*
          * copy_pmd_range()'s prior pmd_none_or_clear_bad(src_pmd), and the
          * error handling here, assume that exclusive mmap_lock on dst and src
          * protects anon from unexpected THP transitions; with shmem and file
          * protected by mmap_lock-less collapse skipping areas with anon_vma
          * (whereas vma_needs_copy() skips areas without anon_vma).  A rework
          * can remove such assumptions later, but this is good enough for now.
          */
         dst_pte = pte_alloc_map_lock(dst_mm, dst_pmd, addr, &dst_ptl);
         if (!dst_pte) {
                 ret = -ENOMEM;
                 goto out;
         }
         src_pte = pte_offset_map_nolock(src_mm, src_pmd, addr, &src_ptl);
         if (!src_pte) {
                 pte_unmap_unlock(dst_pte, dst_ptl);
                 /* ret == 0 */
                 goto out;
         }
         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
         orig_src_pte = src_pte;
         orig_dst_pte = dst_pte;
         arch_enter_lazy_mmu_mode();
 
         do {
                 nr = 1;
 
                 /*
                  * We are holding two locks at this point - either of them
                  * could generate latencies in another task on another CPU.
                  */
                 if (progress >= 32) {
                         progress = 0;
                         if (need_resched() ||
                             spin_needbreak(src_ptl) || spin_needbreak(dst_ptl))
                                 break;
                 }
                 ptent = ptep_get(src_pte);
                 if (pte_none(ptent)) {
                         progress++;
                         continue;
                 }
                 if (unlikely(!pte_present(ptent))) {
                         ret = copy_nonpresent_pte(dst_mm, src_mm,
                                                   dst_pte, src_pte,
                                                   dst_vma, src_vma,
                                                   addr, rss);
                         if (ret == -EIO) {
                                 entry = pte_to_swp_entry(ptep_get(src_pte));
                                 break;
                         } else if (ret == -EBUSY) {
                                 break;
                         } else if (!ret) {
                                 progress += 8;
                                 continue;
                         }
                         ptent = ptep_get(src_pte);
                         VM_WARN_ON_ONCE(!pte_present(ptent));
 
                         /*
                          * Device exclusive entry restored, continue by copying
                          * the now present pte.
                          */
                         WARN_ON_ONCE(ret != -ENOENT);
                 }
                 /* copy_present_ptes() will clear `*prealloc' if consumed */
                 max_nr = (end - addr) / PAGE_SIZE;
                 ret = copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte,
                                         ptent, addr, max_nr, rss, &prealloc);
                 /*
                  * If we need a pre-allocated page for this pte, drop the
                  * locks, allocate, and try again.
                  */
                 if (unlikely(ret == -EAGAIN))
                         break;
                 if (unlikely(prealloc)) {
                         /*
                          * pre-alloc page cannot be reused by next time so as
                          * to strictly follow mempolicy (e.g., alloc_page_vma()
                          * will allocate page according to address).  This
                          * could only happen if one pinned pte changed.
                          */
                         folio_put(prealloc);
                         prealloc = NULL;
                 }
                 nr = ret;
                 progress += 8 * nr;
         } while (dst_pte += nr, src_pte += nr, addr += PAGE_SIZE * nr,
                  addr != end);
 
         arch_leave_lazy_mmu_mode();
         pte_unmap_unlock(orig_src_pte, src_ptl);
         add_mm_rss_vec(dst_mm, rss);
         pte_unmap_unlock(orig_dst_pte, dst_ptl);
         cond_resched();
 
         if (ret == -EIO) {
                 VM_WARN_ON_ONCE(!entry.val);
                 if (add_swap_count_continuation(entry, GFP_KERNEL) < 0) {
                         ret = -ENOMEM;
                         goto out;
                 }
                 entry.val = 0;
         } else if (ret == -EBUSY) {
                 goto out;
         } else if (ret ==  -EAGAIN) {
                 prealloc = folio_prealloc(src_mm, src_vma, addr, false);
                 if (!prealloc)
                         return -ENOMEM;
         } else if (ret < 0) {
                 VM_WARN_ON_ONCE(1);
         }
 
         /* We've captured and resolved the error. Reset, try again. */
         ret = 0;
 
         if (addr != end)
                 goto again;
 out:
         if (unlikely(prealloc))
                 folio_put(prealloc);
         return ret;
 }
 
 static inline int
 copy_pmd_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
                pud_t *dst_pud, pud_t *src_pud, unsigned long addr,
                unsigned long end)
 {
         struct mm_struct *dst_mm = dst_vma->vm_mm;
         struct mm_struct *src_mm = src_vma->vm_mm;
         pmd_t *src_pmd, *dst_pmd;
         unsigned long next;
 
         dst_pmd = pmd_alloc(dst_mm, dst_pud, addr);
         if (!dst_pmd)
                 return -ENOMEM;
         src_pmd = pmd_offset(src_pud, addr);
         do {
                 next = pmd_addr_end(addr, end);
                 if (is_swap_pmd(*src_pmd) || pmd_trans_huge(*src_pmd)
                         || pmd_devmap(*src_pmd)) {
                         int err;
                         VM_BUG_ON_VMA(next-addr != HPAGE_PMD_SIZE, src_vma);
                         err = copy_huge_pmd(dst_mm, src_mm, dst_pmd, src_pmd,
                                             addr, dst_vma, src_vma);
                         if (err == -ENOMEM)
                                 return -ENOMEM;
                         if (!err)
                                 continue;
                         /* fall through */
                 }
                 if (pmd_none_or_clear_bad(src_pmd))
                         continue;
                 if (copy_pte_range(dst_vma, src_vma, dst_pmd, src_pmd,
                                    addr, next))
                         return -ENOMEM;
         } while (dst_pmd++, src_pmd++, addr = next, addr != end);
         return 0;
 }
 
 static inline int
 copy_pud_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
                p4d_t *dst_p4d, p4d_t *src_p4d, unsigned long addr,
                unsigned long end)
 {
         struct mm_struct *dst_mm = dst_vma->vm_mm;
         struct mm_struct *src_mm = src_vma->vm_mm;
         pud_t *src_pud, *dst_pud;
         unsigned long next;
 
         dst_pud = pud_alloc(dst_mm, dst_p4d, addr);
         if (!dst_pud)
                 return -ENOMEM;
         src_pud = pud_offset(src_p4d, addr);
         do {
                 next = pud_addr_end(addr, end);
                 if (pud_trans_huge(*src_pud) || pud_devmap(*src_pud)) {
                         int err;
 
                         VM_BUG_ON_VMA(next-addr != HPAGE_PUD_SIZE, src_vma);
                         err = copy_huge_pud(dst_mm, src_mm,
                                             dst_pud, src_pud, addr, src_vma);
                         if (err == -ENOMEM)
                                 return -ENOMEM;
                         if (!err)
                                 continue;
                         /* fall through */
                 }
                 if (pud_none_or_clear_bad(src_pud))
                         continue;
                 if (copy_pmd_range(dst_vma, src_vma, dst_pud, src_pud,
                                    addr, next))
                         return -ENOMEM;
         } while (dst_pud++, src_pud++, addr = next, addr != end);
         return 0;
 }
 
 static inline int
 copy_p4d_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
                pgd_t *dst_pgd, pgd_t *src_pgd, unsigned long addr,
                unsigned long end)
 {
         struct mm_struct *dst_mm = dst_vma->vm_mm;
         p4d_t *src_p4d, *dst_p4d;
         unsigned long next;
 
         dst_p4d = p4d_alloc(dst_mm, dst_pgd, addr);
         if (!dst_p4d)
                 return -ENOMEM;
         src_p4d = p4d_offset(src_pgd, addr);
         do {
                 next = p4d_addr_end(addr, end);
                 if (p4d_none_or_clear_bad(src_p4d))
                         continue;
                 if (copy_pud_range(dst_vma, src_vma, dst_p4d, src_p4d,
                                    addr, next))
                         return -ENOMEM;
         } while (dst_p4d++, src_p4d++, addr = next, addr != end);
         return 0;
 }
 
 /*
  * Return true if the vma needs to copy the pgtable during this fork().  Return
  * false when we can speed up fork() by allowing lazy page faults later until
  * when the child accesses the memory range.
  */
 static bool
 vma_needs_copy(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
 {
         /*
          * Always copy pgtables when dst_vma has uffd-wp enabled even if it's
          * file-backed (e.g. shmem). Because when uffd-wp is enabled, pgtable
          * contains uffd-wp protection information, that's something we can't
          * retrieve from page cache, and skip copying will lose those info.
          */
         if (userfaultfd_wp(dst_vma))
                 return true;
 
         if (src_vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
                 return true;
 
         if (src_vma->anon_vma)
                 return true;
 
         /*
          * Don't copy ptes where a page fault will fill them correctly.  Fork
          * becomes much lighter when there are big shared or private readonly
          * mappings. The tradeoff is that copy_page_range is more efficient
          * than faulting.
          */
         return false;
 }
 
 int
 copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
 {
         pgd_t *src_pgd, *dst_pgd;
         unsigned long next;
         unsigned long addr = src_vma->vm_start;
         unsigned long end = src_vma->vm_end;
         struct mm_struct *dst_mm = dst_vma->vm_mm;
         struct mm_struct *src_mm = src_vma->vm_mm;
         struct mmu_notifier_range range;
         bool is_cow;
         int ret;
 
         if (!vma_needs_copy(dst_vma, src_vma))
                 return 0;
 
         if (is_vm_hugetlb_page(src_vma))
                 return copy_hugetlb_page_range(dst_mm, src_mm, dst_vma, src_vma);
 
         if (unlikely(src_vma->vm_flags & VM_PFNMAP)) {
                 /*
                  * We do not free on error cases below as remove_vma
                  * gets called on error from higher level routine
                  */
                 ret = track_pfn_copy(src_vma);
                 if (ret)
                         return ret;
         }
 
         /*
          * We need to invalidate the secondary MMU mappings only when
          * there could be a permission downgrade on the ptes of the
          * parent mm. And a permission downgrade will only happen if
          * is_cow_mapping() returns true.
          */
         is_cow = is_cow_mapping(src_vma->vm_flags);
 
         if (is_cow) {
                 mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_PAGE,
                                         0, src_mm, addr, end);
                 mmu_notifier_invalidate_range_start(&range);
                 /*
                  * Disabling preemption is not needed for the write side, as
                  * the read side doesn't spin, but goes to the mmap_lock.
                  *
                  * Use the raw variant of the seqcount_t write API to avoid
                  * lockdep complaining about preemptibility.
                  */
                 vma_assert_write_locked(src_vma);
                 raw_write_seqcount_begin(&src_mm->write_protect_seq);
         }
 
         ret = 0;
         dst_pgd = pgd_offset(dst_mm, addr);
         src_pgd = pgd_offset(src_mm, addr);
         do {
                 next = pgd_addr_end(addr, end);
                 if (pgd_none_or_clear_bad(src_pgd))
                         continue;
                 if (unlikely(copy_p4d_range(dst_vma, src_vma, dst_pgd, src_pgd,
                                             addr, next))) {
                         untrack_pfn_clear(dst_vma);
                         ret = -ENOMEM;
                         break;
                 }
         } while (dst_pgd++, src_pgd++, addr = next, addr != end);
 
         if (is_cow) {
                 raw_write_seqcount_end(&src_mm->write_protect_seq);
                 mmu_notifier_invalidate_range_end(&range);
         }
         return ret;
 }
 
 /* Whether we should zap all COWed (private) pages too */
 static inline bool should_zap_cows(struct zap_details *details)
 {
         /* By default, zap all pages */
         if (!details)
                 return true;
 
         /* Or, we zap COWed pages only if the caller wants to */
         return details->even_cows;
 }
 
 /* Decides whether we should zap this folio with the folio pointer specified */
 static inline bool should_zap_folio(struct zap_details *details,
                                     struct folio *folio)
 {
         /* If we can make a decision without *folio.. */
         if (should_zap_cows(details))
                 return true;
 
         /* Otherwise we should only zap non-anon folios */
         return !folio_test_anon(folio);
 }
 
 static inline bool zap_drop_file_uffd_wp(struct zap_details *details)
 {
         if (!details)
                 return false;
 
         return details->zap_flags & ZAP_FLAG_DROP_MARKER;
 }
 
 /*
  * This function makes sure that we'll replace the none pte with an uffd-wp
  * swap special pte marker when necessary. Must be with the pgtable lock held.
  */
 static inline void
 zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
                               unsigned long addr, pte_t *pte, int nr,
                               struct zap_details *details, pte_t pteval)
 {
         /* Zap on anonymous always means dropping everything */
         if (vma_is_anonymous(vma))
                 return;
 
         if (zap_drop_file_uffd_wp(details))
                 return;
 
         for (;;) {
                 /* the PFN in the PTE is irrelevant. */
                 pte_install_uffd_wp_if_needed(vma, addr, pte, pteval);
                 if (--nr == 0)
                         break;
                 pte++;
                 addr += PAGE_SIZE;
         }
 }
 
 static __always_inline void zap_present_folio_ptes(struct mmu_gather *tlb,
                 struct vm_area_struct *vma, struct folio *folio,
                 struct page *page, pte_t *pte, pte_t ptent, unsigned int nr,
                 unsigned long addr, struct zap_details *details, int *rss,
                 bool *force_flush, bool *force_break)
 {
         struct mm_struct *mm = tlb->mm;
         bool delay_rmap = false;
 
         if (!folio_test_anon(folio)) {
                 ptent = get_and_clear_full_ptes(mm, addr, pte, nr, tlb->fullmm);
                 if (pte_dirty(ptent)) {
                         folio_mark_dirty(folio);
                         if (tlb_delay_rmap(tlb)) {
                                 delay_rmap = true;
                                 *force_flush = true;
                         }
                 }
                 if (pte_young(ptent) && likely(vma_has_recency(vma)))
                         folio_mark_accessed(folio);
                 rss[mm_counter(folio)] -= nr;
         } else {
                 /* We don't need up-to-date accessed/dirty bits. */
                 clear_full_ptes(mm, addr, pte, nr, tlb->fullmm);
                 rss[MM_ANONPAGES] -= nr;
         }
         /* Checking a single PTE in a batch is sufficient. */
         arch_check_zapped_pte(vma, ptent);
         tlb_remove_tlb_entries(tlb, pte, nr, addr);
         if (unlikely(userfaultfd_pte_wp(vma, ptent)))
                 zap_install_uffd_wp_if_needed(vma, addr, pte, nr, details,
                                               ptent);
 
         if (!delay_rmap) {
                 folio_remove_rmap_ptes(folio, page, nr, vma);
 
                 if (unlikely(folio_mapcount(folio) < 0))
                         print_bad_pte(vma, addr, ptent, page);
         }
         if (unlikely(__tlb_remove_folio_pages(tlb, page, nr, delay_rmap))) {
                 *force_flush = true;
                 *force_break = true;
         }
 }
 
 /*
  * Zap or skip at least one present PTE, trying to batch-process subsequent
  * PTEs that map consecutive pages of the same folio.
  *
  * Returns the number of processed (skipped or zapped) PTEs (at least 1).
  */
 static inline int zap_present_ptes(struct mmu_gather *tlb,
                 struct vm_area_struct *vma, pte_t *pte, pte_t ptent,
                 unsigned int max_nr, unsigned long addr,
                 struct zap_details *details, int *rss, bool *force_flush,
                 bool *force_break)
 {
         const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
         struct mm_struct *mm = tlb->mm;
         struct folio *folio;
         struct page *page;
         int nr;
 
         page = vm_normal_page(vma, addr, ptent);
         if (!page) {
                 /* We don't need up-to-date accessed/dirty bits. */
                 ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
                 arch_check_zapped_pte(vma, ptent);
                 tlb_remove_tlb_entry(tlb, pte, addr);
                 if (userfaultfd_pte_wp(vma, ptent))
                         zap_install_uffd_wp_if_needed(vma, addr, pte, 1,
                                                       details, ptent);
                 ksm_might_unmap_zero_page(mm, ptent);
                 return 1;
         }
 
         folio = page_folio(page);
         if (unlikely(!should_zap_folio(details, folio)))
                 return 1;
 
         /*
          * Make sure that the common "small folio" case is as fast as possible
          * by keeping the batching logic separate.
          */
         if (unlikely(folio_test_large(folio) && max_nr != 1)) {
                 nr = folio_pte_batch(folio, addr, pte, ptent, max_nr, fpb_flags,
                                      NULL, NULL, NULL);
 
                 zap_present_folio_ptes(tlb, vma, folio, page, pte, ptent, nr,
                                        addr, details, rss, force_flush,
                                        force_break);
                 return nr;
         }
         zap_present_folio_ptes(tlb, vma, folio, page, pte, ptent, 1, addr,
                                details, rss, force_flush, force_break);
         return 1;
 }
 
 static unsigned long zap_pte_range(struct mmu_gather *tlb,
                                 struct vm_area_struct *vma, pmd_t *pmd,
                                 unsigned long addr, unsigned long end,
                                 struct zap_details *details)
 {
         bool force_flush = false, force_break = false;
         struct mm_struct *mm = tlb->mm;
         int rss[NR_MM_COUNTERS];
         spinlock_t *ptl;
         pte_t *start_pte;
         pte_t *pte;
         swp_entry_t entry;
         int nr;
 
         tlb_change_page_size(tlb, PAGE_SIZE);
         init_rss_vec(rss);
         start_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
         if (!pte)
                 return addr;
 
         flush_tlb_batched_pending(mm);
         arch_enter_lazy_mmu_mode();
         do {
                 pte_t ptent = ptep_get(pte);
                 struct folio *folio;
                 struct page *page;
                 int max_nr;
 
                 nr = 1;
                 if (pte_none(ptent))
                         continue;
 
                 if (need_resched())
                         break;
 
                 if (pte_present(ptent)) {
                         max_nr = (end - addr) / PAGE_SIZE;
                         nr = zap_present_ptes(tlb, vma, pte, ptent, max_nr,
                                               addr, details, rss, &force_flush,
                                               &force_break);
                         if (unlikely(force_break)) {
                                 addr += nr * PAGE_SIZE;
                                 break;
                         }
                         continue;
                 }
 
                 entry = pte_to_swp_entry(ptent);
                 if (is_device_private_entry(entry) ||
                     is_device_exclusive_entry(entry)) {
                         page = pfn_swap_entry_to_page(entry);
                         folio = page_folio(page);
                         if (unlikely(!should_zap_folio(details, folio)))
                                 continue;
                         /*
                          * Both device private/exclusive mappings should only
                          * work with anonymous page so far, so we don't need to
                          * consider uffd-wp bit when zap. For more information,
                          * see zap_install_uffd_wp_if_needed().
                          */
                         WARN_ON_ONCE(!vma_is_anonymous(vma));
                         rss[mm_counter(folio)]--;
                         if (is_device_private_entry(entry))
                                 folio_remove_rmap_pte(folio, page, vma);
                         folio_put(folio);
                 } else if (!non_swap_entry(entry)) {
                         max_nr = (end - addr) / PAGE_SIZE;
                         nr = swap_pte_batch(pte, max_nr, ptent);
                         /* Genuine swap entries, hence a private anon pages */
                         if (!should_zap_cows(details))
                                 continue;
                         rss[MM_SWAPENTS] -= nr;
                         free_swap_and_cache_nr(entry, nr);
                 } else if (is_migration_entry(entry)) {
                         folio = pfn_swap_entry_folio(entry);
                         if (!should_zap_folio(details, folio))
                                 continue;
                         rss[mm_counter(folio)]--;
                 } else if (pte_marker_entry_uffd_wp(entry)) {
                         /*
                          * For anon: always drop the marker; for file: only
                          * drop the marker if explicitly requested.
                          */
                         if (!vma_is_anonymous(vma) &&
                             !zap_drop_file_uffd_wp(details))
                                 continue;
                 } else if (is_hwpoison_entry(entry) ||
                            is_poisoned_swp_entry(entry)) {
                         if (!should_zap_cows(details))
                                 continue;
                 } else {
                         /* We should have covered all the swap entry types */
                         pr_alert("unrecognized swap entry 0x%lx\n", entry.val);
                         WARN_ON_ONCE(1);
                 }
                 clear_not_present_full_ptes(mm, addr, pte, nr, tlb->fullmm);
                 zap_install_uffd_wp_if_needed(vma, addr, pte, nr, details, ptent);
         } while (pte += nr, addr += PAGE_SIZE * nr, addr != end);
 
         add_mm_rss_vec(mm, rss);
         arch_leave_lazy_mmu_mode();
 
         /* Do the actual TLB flush before dropping ptl */
         if (force_flush) {
                 tlb_flush_mmu_tlbonly(tlb);
                 tlb_flush_rmaps(tlb, vma);
         }
         pte_unmap_unlock(start_pte, ptl);
 
         /*
          * If we forced a TLB flush (either due to running out of
          * batch buffers or because we needed to flush dirty TLB
          * entries before releasing the ptl), free the batched
          * memory too. Come back again if we didn't do everything.
          */
         if (force_flush)
                 tlb_flush_mmu(tlb);
 
         return addr;
 }
 
 static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
                                 struct vm_area_struct *vma, pud_t *pud,
                                 unsigned long addr, unsigned long end,
                                 struct zap_details *details)
 {
         pmd_t *pmd;
         unsigned long next;
 
         pmd = pmd_offset(pud, addr);
         do {
                 next = pmd_addr_end(addr, end);
                 if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
                         if (next - addr != HPAGE_PMD_SIZE)
                                 __split_huge_pmd(vma, pmd, addr, false, NULL);
                         else if (zap_huge_pmd(tlb, vma, pmd, addr)) {
                                 addr = next;
                                 continue;
                         }
                         /* fall through */
                 } else if (details && details->single_folio &&
                            folio_test_pmd_mappable(details->single_folio) &&
                            next - addr == HPAGE_PMD_SIZE && pmd_none(*pmd)) {
                         spinlock_t *ptl = pmd_lock(tlb->mm, pmd);
                         /*
                          * Take and drop THP pmd lock so that we cannot return
                          * prematurely, while zap_huge_pmd() has cleared *pmd,
                          * but not yet decremented compound_mapcount().
                          */
                         spin_unlock(ptl);
                 }
                 if (pmd_none(*pmd)) {
                         addr = next;
                         continue;
                 }
                 addr = zap_pte_range(tlb, vma, pmd, addr, next, details);
                 if (addr != next)
                         pmd--;
         } while (pmd++, cond_resched(), addr != end);
 
         return addr;
 }
 
 static inline unsigned long zap_pud_range(struct mmu_gather *tlb,
                                 struct vm_area_struct *vma, p4d_t *p4d,
                                 unsigned long addr, unsigned long end,
                                 struct zap_details *details)
 {
         pud_t *pud;
         unsigned long next;
 
         pud = pud_offset(p4d, addr);
         do {
                 next = pud_addr_end(addr, end);
                 if (pud_trans_huge(*pud) || pud_devmap(*pud)) {
                         if (next - addr != HPAGE_PUD_SIZE) {
                                 mmap_assert_locked(tlb->mm);
                                 split_huge_pud(vma, pud, addr);
                         } else if (zap_huge_pud(tlb, vma, pud, addr))
                                 goto next;
                         /* fall through */
                 }
                 if (pud_none_or_clear_bad(pud))
                         continue;
                 next = zap_pmd_range(tlb, vma, pud, addr, next, details);
 next:
                 cond_resched();
         } while (pud++, addr = next, addr != end);
 
         return addr;
 }
 
 static inline unsigned long zap_p4d_range(struct mmu_gather *tlb,
                                 struct vm_area_struct *vma, pgd_t *pgd,
                                 unsigned long addr, unsigned long end,
                                 struct zap_details *details)
 {
         p4d_t *p4d;
         unsigned long next;
 
         p4d = p4d_offset(pgd, addr);
         do {
                 next = p4d_addr_end(addr, end);
                 if (p4d_none_or_clear_bad(p4d))
                         continue;
                 next = zap_pud_range(tlb, vma, p4d, addr, next, details);
         } while (p4d++, addr = next, addr != end);
 
         return addr;
 }
 
 void unmap_page_range(struct mmu_gather *tlb,
                              struct vm_area_struct *vma,
                              unsigned long addr, unsigned long end,
                              struct zap_details *details)
 {
         pgd_t *pgd;
         unsigned long next;
 
         BUG_ON(addr >= end);
         tlb_start_vma(tlb, vma);
         pgd = pgd_offset(vma->vm_mm, addr);
         do {
                 next = pgd_addr_end(addr, end);
                 if (pgd_none_or_clear_bad(pgd))
                         continue;
                 next = zap_p4d_range(tlb, vma, pgd, addr, next, details);
         } while (pgd++, addr = next, addr != end);
         tlb_end_vma(tlb, vma);
 }
 
 
 static void unmap_single_vma(struct mmu_gather *tlb,
                 struct vm_area_struct *vma, unsigned long start_addr,
                 unsigned long end_addr,
                 struct zap_details *details, bool mm_wr_locked)
 {
         unsigned long start = max(vma->vm_start, start_addr);
         unsigned long end;
 
         if (start >= vma->vm_end)
                 return;
         end = min(vma->vm_end, end_addr);
         if (end <= vma->vm_start)
                 return;
 
         if (vma->vm_file)
                 uprobe_munmap(vma, start, end);
 
         if (unlikely(vma->vm_flags & VM_PFNMAP))
                 untrack_pfn(vma, 0, 0, mm_wr_locked);
 
         if (start != end) {
                 if (unlikely(is_vm_hugetlb_page(vma))) {
                         /*
                          * It is undesirable to test vma->vm_file as it
                          * should be non-null for valid hugetlb area.
                          * However, vm_file will be NULL in the error
                          * cleanup path of mmap_region. When
                          * hugetlbfs ->mmap method fails,
                          * mmap_region() nullifies vma->vm_file
                          * before calling this function to clean up.
                          * Since no pte has actually been setup, it is
                          * safe to do nothing in this case.
                          */
                         if (vma->vm_file) {
                                 zap_flags_t zap_flags = details ?
                                     details->zap_flags : 0;
                                 __unmap_hugepage_range(tlb, vma, start, end,
                                                              NULL, zap_flags);
                         }
                 } else
                         unmap_page_range(tlb, vma, start, end, details);
         }
 }
 
 /**
  * unmap_vmas - unmap a range of memory covered by a list of vma's
  * @tlb: address of the caller's struct mmu_gather
  * @mas: the maple state
  * @vma: the starting vma
  * @start_addr: virtual address at which to start unmapping
  * @end_addr: virtual address at which to end unmapping
  * @tree_end: The maximum index to check
  * @mm_wr_locked: lock flag
  *
  * Unmap all pages in the vma list.
  *
  * Only addresses between `start' and `end' will be unmapped.
  *
  * The VMA list must be sorted in ascending virtual address order.
  *
  * unmap_vmas() assumes that the caller will flush the whole unmapped address
  * range after unmap_vmas() returns.  So the only responsibility here is to
  * ensure that any thus-far unmapped pages are flushed before unmap_vmas()
  * drops the lock and schedules.
  */
 void unmap_vmas(struct mmu_gather *tlb, struct ma_state *mas,
                 struct vm_area_struct *vma, unsigned long start_addr,
                 unsigned long end_addr, unsigned long tree_end,
                 bool mm_wr_locked)
 {
         struct mmu_notifier_range range;
         struct zap_details details = {
                 .zap_flags = ZAP_FLAG_DROP_MARKER | ZAP_FLAG_UNMAP,
                 /* Careful - we need to zap private pages too! */
                 .even_cows = true,
         };
 
         mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma->vm_mm,
                                 start_addr, end_addr);
         mmu_notifier_invalidate_range_start(&range);
         do {
                 unsigned long start = start_addr;
                 unsigned long end = end_addr;
                 hugetlb_zap_begin(vma, &start, &end);
                 unmap_single_vma(tlb, vma, start, end, &details,
                                  mm_wr_locked);
                 hugetlb_zap_end(vma, &details);
                 vma = mas_find(mas, tree_end - 1);
         } while (vma && likely(!xa_is_zero(vma)));
         mmu_notifier_invalidate_range_end(&range);
 }
 
 /**
  * zap_page_range_single - remove user pages in a given range
  * @vma: vm_area_struct holding the applicable pages
  * @address: starting address of pages to zap
  * @size: number of bytes to zap
  * @details: details of shared cache invalidation
  *
  * The range must fit into one VMA.
  */
 void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
                 unsigned long size, struct zap_details *details)
 {
         const unsigned long end = address + size;
         struct mmu_notifier_range range;
         struct mmu_gather tlb;
 
         lru_add_drain();
         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
                                 address, end);
         hugetlb_zap_begin(vma, &range.start, &range.end);
         tlb_gather_mmu(&tlb, vma->vm_mm);
         update_hiwater_rss(vma->vm_mm);
         mmu_notifier_invalidate_range_start(&range);
         /*
          * unmap 'address-end' not 'range.start-range.end' as range
          * could have been expanded for hugetlb pmd sharing.
          */
         unmap_single_vma(&tlb, vma, address, end, details, false);
         mmu_notifier_invalidate_range_end(&range);
         tlb_finish_mmu(&tlb);
         hugetlb_zap_end(vma, details);
 }
 
 /**
  * zap_vma_ptes - remove ptes mapping the vma
  * @vma: vm_area_struct holding ptes to be zapped
  * @address: starting address of pages to zap
  * @size: number of bytes to zap
  *
  * This function only unmaps ptes assigned to VM_PFNMAP vmas.
  *
  * The entire address range must be fully contained within the vma.
  *
  */
 void zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
                 unsigned long size)
 {
         if (!range_in_vma(vma, address, address + size) ||
                         !(vma->vm_flags & VM_PFNMAP))
                 return;
 
         zap_page_range_single(vma, address, size, NULL);
 }
 EXPORT_SYMBOL_GPL(zap_vma_ptes);
 
 static pmd_t *walk_to_pmd(struct mm_struct *mm, unsigned long addr)
 {
         pgd_t *pgd;
         p4d_t *p4d;
         pud_t *pud;
         pmd_t *pmd;
 
         pgd = pgd_offset(mm, addr);
         p4d = p4d_alloc(mm, pgd, addr);
         if (!p4d)
                 return NULL;
         pud = pud_alloc(mm, p4d, addr);
         if (!pud)
                 return NULL;
         pmd = pmd_alloc(mm, pud, addr);
         if (!pmd)
                 return NULL;
 
         VM_BUG_ON(pmd_trans_huge(*pmd));
         return pmd;
 }
 
 pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
                         spinlock_t **ptl)
 {
         pmd_t *pmd = walk_to_pmd(mm, addr);
 
         if (!pmd)
                 return NULL;
         return pte_alloc_map_lock(mm, pmd, addr, ptl);
 }
 
 static bool vm_mixed_zeropage_allowed(struct vm_area_struct *vma)
 {
         VM_WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP);
         /*
          * Whoever wants to forbid the zeropage after some zeropages
          * might already have been mapped has to scan the page tables and
          * bail out on any zeropages. Zeropages in COW mappings can
          * be unshared using FAULT_FLAG_UNSHARE faults.
          */
         if (mm_forbids_zeropage(vma->vm_mm))
                 return false;
         /* zeropages in COW mappings are common and unproblematic. */
         if (is_cow_mapping(vma->vm_flags))
                 return true;
         /* Mappings that do not allow for writable PTEs are unproblematic. */
         if (!(vma->vm_flags & (VM_WRITE | VM_MAYWRITE)))
                 return true;
         /*
          * Why not allow any VMA that has vm_ops->pfn_mkwrite? GUP could
          * find the shared zeropage and longterm-pin it, which would
          * be problematic as soon as the zeropage gets replaced by a different
          * page due to vma->vm_ops->pfn_mkwrite, because what's mapped would
          * now differ to what GUP looked up. FSDAX is incompatible to
          * FOLL_LONGTERM and VM_IO is incompatible to GUP completely (see
          * check_vma_flags).
          */
         return vma->vm_ops && vma->vm_ops->pfn_mkwrite &&
                (vma_is_fsdax(vma) || vma->vm_flags & VM_IO);
 }
 
 static int validate_page_before_insert(struct vm_area_struct *vma,
                                        struct page *page)
 {
         struct folio *folio = page_folio(page);
 
         if (!folio_ref_count(folio))
                 return -EINVAL;
         if (unlikely(is_zero_folio(folio))) {
                 if (!vm_mixed_zeropage_allowed(vma))
                         return -EINVAL;
                 return 0;
         }
         if (folio_test_anon(folio) || folio_test_slab(folio) ||
             page_has_type(page))
                 return -EINVAL;
         flush_dcache_folio(folio);
         return 0;
 }
 
 static int insert_page_into_pte_locked(struct vm_area_struct *vma, pte_t *pte,
                         unsigned long addr, struct page *page, pgprot_t prot)
 {
         struct folio *folio = page_folio(page);
         pte_t pteval;
 
         if (!pte_none(ptep_get(pte)))
                 return -EBUSY;
         /* Ok, finally just insert the thing.. */
         pteval = mk_pte(page, prot);
         if (unlikely(is_zero_folio(folio))) {
                 pteval = pte_mkspecial(pteval);
         } else {
                 folio_get(folio);
                 inc_mm_counter(vma->vm_mm, mm_counter_file(folio));
                 folio_add_file_rmap_pte(folio, page, vma);
         }
         set_pte_at(vma->vm_mm, addr, pte, pteval);
         return 0;
 }
 
 static int insert_page(struct vm_area_struct *vma, unsigned long addr,
                         struct page *page, pgprot_t prot)
 {
         int retval;
         pte_t *pte;
         spinlock_t *ptl;
 
         retval = validate_page_before_insert(vma, page);
         if (retval)
                 goto out;
         retval = -ENOMEM;
         pte = get_locked_pte(vma->vm_mm, addr, &ptl);
         if (!pte)
                 goto out;
         retval = insert_page_into_pte_locked(vma, pte, addr, page, prot);
         pte_unmap_unlock(pte, ptl);
 out:
         return retval;
 }
 
 static int insert_page_in_batch_locked(struct vm_area_struct *vma, pte_t *pte,
                         unsigned long addr, struct page *page, pgprot_t prot)
 {
         int err;
 
         err = validate_page_before_insert(vma, page);
         if (err)
                 return err;
         return insert_page_into_pte_locked(vma, pte, addr, page, prot);
 }
 
 /* insert_pages() amortizes the cost of spinlock operations
  * when inserting pages in a loop.
  */
 static int insert_pages(struct vm_area_struct *vma, unsigned long addr,
                         struct page **pages, unsigned long *num, pgprot_t prot)
 {
         pmd_t *pmd = NULL;
         pte_t *start_pte, *pte;
         spinlock_t *pte_lock;
         struct mm_struct *const mm = vma->vm_mm;
         unsigned long curr_page_idx = 0;
         unsigned long remaining_pages_total = *num;
         unsigned long pages_to_write_in_pmd;
         int ret;
 more:
         ret = -EFAULT;
         pmd = walk_to_pmd(mm, addr);
         if (!pmd)
                 goto out;
 
         pages_to_write_in_pmd = min_t(unsigned long,
                 remaining_pages_total, PTRS_PER_PTE - pte_index(addr));
 
         /* Allocate the PTE if necessary; takes PMD lock once only. */
         ret = -ENOMEM;
         if (pte_alloc(mm, pmd))
                 goto out;
 
         while (pages_to_write_in_pmd) {
                 int pte_idx = 0;
                 const int batch_size = min_t(int, pages_to_write_in_pmd, 8);
 
                 start_pte = pte_offset_map_lock(mm, pmd, addr, &pte_lock);
                 if (!start_pte) {
                         ret = -EFAULT;
                         goto out;
                 }
                 for (pte = start_pte; pte_idx < batch_size; ++pte, ++pte_idx) {
                         int err = insert_page_in_batch_locked(vma, pte,
                                 addr, pages[curr_page_idx], prot);
                         if (unlikely(err)) {
                                 pte_unmap_unlock(start_pte, pte_lock);
                                 ret = err;
                                 remaining_pages_total -= pte_idx;
                                 goto out;
                         }
                         addr += PAGE_SIZE;
                         ++curr_page_idx;
                 }
                 pte_unmap_unlock(start_pte, pte_lock);
                 pages_to_write_in_pmd -= batch_size;
                 remaining_pages_total -= batch_size;
         }
         if (remaining_pages_total)
                 goto more;
         ret = 0;
 out:
         *num = remaining_pages_total;
         return ret;
 }
 
 /**
  * vm_insert_pages - insert multiple pages into user vma, batching the pmd lock.
  * @vma: user vma to map to
  * @addr: target start user address of these pages
  * @pages: source kernel pages
  * @num: in: number of pages to map. out: number of pages that were *not*
  * mapped. (0 means all pages were successfully mapped).
  *
  * Preferred over vm_insert_page() when inserting multiple pages.
  *
  * In case of error, we may have mapped a subset of the provided
  * pages. It is the caller's responsibility to account for this case.
  *
  * The same restrictions apply as in vm_insert_page().
  */
 int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
                         struct page **pages, unsigned long *num)
 {
         const unsigned long end_addr = addr + (*num * PAGE_SIZE) - 1;
 
         if (addr < vma->vm_start || end_addr >= vma->vm_end)
                 return -EFAULT;
         if (!(vma->vm_flags & VM_MIXEDMAP)) {
                 BUG_ON(mmap_read_trylock(vma->vm_mm));
                 BUG_ON(vma->vm_flags & VM_PFNMAP);
                 vm_flags_set(vma, VM_MIXEDMAP);
         }
         /* Defer page refcount checking till we're about to map that page. */
         return insert_pages(vma, addr, pages, num, vma->vm_page_prot);
 }
 EXPORT_SYMBOL(vm_insert_pages);
 
 /**
  * vm_insert_page - insert single page into user vma
  * @vma: user vma to map to
  * @addr: target user address of this page
  * @page: source kernel page
  *
  * This allows drivers to insert individual pages they've allocated
  * into a user vma. The zeropage is supported in some VMAs,
  * see vm_mixed_zeropage_allowed().
  *
  * The page has to be a nice clean _individual_ kernel allocation.
  * If you allocate a compound page, you need to have marked it as
  * such (__GFP_COMP), or manually just split the page up yourself
  * (see split_page()).
  *
  * NOTE! Traditionally this was done with "remap_pfn_range()" which
  * took an arbitrary page protection parameter. This doesn't allow
  * that. Your vma protection will have to be set up correctly, which
  * means that if you want a shared writable mapping, you'd better
  * ask for a shared writable mapping!
  *
  * The page does not need to be reserved.
  *
  * Usually this function is called from f_op->mmap() handler
  * under mm->mmap_lock write-lock, so it can change vma->vm_flags.
  * Caller must set VM_MIXEDMAP on vma if it wants to call this
  * function from other places, for example from page-fault handler.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
                         struct page *page)
 {
         if (addr < vma->vm_start || addr >= vma->vm_end)
                 return -EFAULT;
         if (!(vma->vm_flags & VM_MIXEDMAP)) {
                 BUG_ON(mmap_read_trylock(vma->vm_mm));
                 BUG_ON(vma->vm_flags & VM_PFNMAP);
                 vm_flags_set(vma, VM_MIXEDMAP);
         }
         return insert_page(vma, addr, page, vma->vm_page_prot);
 }
 EXPORT_SYMBOL(vm_insert_page);
 
 /*
  * __vm_map_pages - maps range of kernel pages into user vma
  * @vma: user vma to map to
  * @pages: pointer to array of source kernel pages
  * @num: number of pages in page array
  * @offset: user's requested vm_pgoff
  *
  * This allows drivers to map range of kernel pages into a user vma.
  * The zeropage is supported in some VMAs, see
  * vm_mixed_zeropage_allowed().
  *
  * Return: 0 on success and error code otherwise.
  */
 static int __vm_map_pages(struct vm_area_struct *vma, struct page **pages,
                                 unsigned long num, unsigned long offset)
 {
         unsigned long count = vma_pages(vma);
         unsigned long uaddr = vma->vm_start;
         int ret, i;
 
         /* Fail if the user requested offset is beyond the end of the object */
         if (offset >= num)
                 return -ENXIO;
 
         /* Fail if the user requested size exceeds available object size */
         if (count > num - offset)
                 return -ENXIO;
 
         for (i = 0; i < count; i++) {
                 ret = vm_insert_page(vma, uaddr, pages[offset + i]);
                 if (ret < 0)
                         return ret;
                 uaddr += PAGE_SIZE;
         }
 
         return 0;
 }
 
 /**
  * vm_map_pages - maps range of kernel pages starts with non zero offset
  * @vma: user vma to map to
  * @pages: pointer to array of source kernel pages
  * @num: number of pages in page array
  *
  * Maps an object consisting of @num pages, catering for the user's
  * requested vm_pgoff
  *
  * If we fail to insert any page into the vma, the function will return
  * immediately leaving any previously inserted pages present.  Callers
  * from the mmap handler may immediately return the error as their caller
  * will destroy the vma, removing any successfully inserted pages. Other
  * callers should make their own arrangements for calling unmap_region().
  *
  * Context: Process context. Called by mmap handlers.
  * Return: 0 on success and error code otherwise.
  */
 int vm_map_pages(struct vm_area_struct *vma, struct page **pages,
                                 unsigned long num)
 {
         return __vm_map_pages(vma, pages, num, vma->vm_pgoff);
 }
 EXPORT_SYMBOL(vm_map_pages);
 
 /**
  * vm_map_pages_zero - map range of kernel pages starts with zero offset
  * @vma: user vma to map to
  * @pages: pointer to array of source kernel pages
  * @num: number of pages in page array
  *
  * Similar to vm_map_pages(), except that it explicitly sets the offset
  * to 0. This function is intended for the drivers that did not consider
  * vm_pgoff.
  *
  * Context: Process context. Called by mmap handlers.
  * Return: 0 on success and error code otherwise.
  */
 int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages,
                                 unsigned long num)
 {
         return __vm_map_pages(vma, pages, num, 0);
 }
 EXPORT_SYMBOL(vm_map_pages_zero);
 
 static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
                         pfn_t pfn, pgprot_t prot, bool mkwrite)
 {
         struct mm_struct *mm = vma->vm_mm;
         pte_t *pte, entry;
         spinlock_t *ptl;
 
         pte = get_locked_pte(mm, addr, &ptl);
         if (!pte)
                 return VM_FAULT_OOM;
         entry = ptep_get(pte);
         if (!pte_none(entry)) {
                 if (mkwrite) {
                         /*
                          * For read faults on private mappings the PFN passed
                          * in may not match the PFN we have mapped if the
                          * mapped PFN is a writeable COW page.  In the mkwrite
                          * case we are creating a writable PTE for a shared
                          * mapping and we expect the PFNs to match. If they
                          * don't match, we are likely racing with block
                          * allocation and mapping invalidation so just skip the
                          * update.
                          */
                         if (pte_pfn(entry) != pfn_t_to_pfn(pfn)) {
                                 WARN_ON_ONCE(!is_zero_pfn(pte_pfn(entry)));
                                 goto out_unlock;
                         }
                         entry = pte_mkyoung(entry);
                         entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                         if (ptep_set_access_flags(vma, addr, pte, entry, 1))
                                 update_mmu_cache(vma, addr, pte);
                 }
                 goto out_unlock;
         }
 
         /* Ok, finally just insert the thing.. */
         if (pfn_t_devmap(pfn))
                 entry = pte_mkdevmap(pfn_t_pte(pfn, prot));
         else
                 entry = pte_mkspecial(pfn_t_pte(pfn, prot));
 
         if (mkwrite) {
                 entry = pte_mkyoung(entry);
                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
         }
 
         set_pte_at(mm, addr, pte, entry);
         update_mmu_cache(vma, addr, pte); /* XXX: why not for insert_page? */
 
 out_unlock:
         pte_unmap_unlock(pte, ptl);
         return VM_FAULT_NOPAGE;
 }
 
 /**
  * vmf_insert_pfn_prot - insert single pfn into user vma with specified pgprot
  * @vma: user vma to map to
  * @addr: target user address of this page
  * @pfn: source kernel pfn
  * @pgprot: pgprot flags for the inserted page
  *
  * This is exactly like vmf_insert_pfn(), except that it allows drivers
  * to override pgprot on a per-page basis.
  *
  * This only makes sense for IO mappings, and it makes no sense for
  * COW mappings.  In general, using multiple vmas is preferable;
  * vmf_insert_pfn_prot should only be used if using multiple VMAs is
  * impractical.
  *
  * pgprot typically only differs from @vma->vm_page_prot when drivers set
  * caching- and encryption bits different than those of @vma->vm_page_prot,
  * because the caching- or encryption mode may not be known at mmap() time.
  *
  * This is ok as long as @vma->vm_page_prot is not used by the core vm
  * to set caching and encryption bits for those vmas (except for COW pages).
  * This is ensured by core vm only modifying these page table entries using
  * functions that don't touch caching- or encryption bits, using pte_modify()
  * if needed. (See for example mprotect()).
  *
  * Also when new page-table entries are created, this is only done using the
  * fault() callback, and never using the value of vma->vm_page_prot,
  * except for page-table entries that point to anonymous pages as the result
  * of COW.
  *
  * Context: Process context.  May allocate using %GFP_KERNEL.
  * Return: vm_fault_t value.
  */
 vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
                         unsigned long pfn, pgprot_t pgprot)
 {
         /*
          * Technically, architectures with pte_special can avoid all these
          * restrictions (same for remap_pfn_range).  However we would like
          * consistency in testing and feature parity among all, so we should
          * try to keep these invariants in place for everybody.
          */
         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
                                                 (VM_PFNMAP|VM_MIXEDMAP));
         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
         BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));
 
         if (addr < vma->vm_start || addr >= vma->vm_end)
                 return VM_FAULT_SIGBUS;
 
         if (!pfn_modify_allowed(pfn, pgprot))
                 return VM_FAULT_SIGBUS;
 
         track_pfn_insert(vma, &pgprot, __pfn_to_pfn_t(pfn, PFN_DEV));
 
         return insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot,
                         false);
 }
 EXPORT_SYMBOL(vmf_insert_pfn_prot);
 
 /**
  * vmf_insert_pfn - insert single pfn into user vma
  * @vma: user vma to map to
  * @addr: target user address of this page
  * @pfn: source kernel pfn
  *
  * Similar to vm_insert_page, this allows drivers to insert individual pages
  * they've allocated into a user vma. Same comments apply.
  *
  * This function should only be called from a vm_ops->fault handler, and
  * in that case the handler should return the result of this function.
  *
  * vma cannot be a COW mapping.
  *
  * As this is called only for pages that do not currently exist, we
  * do not need to flush old virtual caches or the TLB.
  *
  * Context: Process context.  May allocate using %GFP_KERNEL.
  * Return: vm_fault_t value.
  */
 vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
                         unsigned long pfn)
 {
         return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot);
 }
 EXPORT_SYMBOL(vmf_insert_pfn);
 
 static bool vm_mixed_ok(struct vm_area_struct *vma, pfn_t pfn, bool mkwrite)
 {
         if (unlikely(is_zero_pfn(pfn_t_to_pfn(pfn))) &&
             (mkwrite || !vm_mixed_zeropage_allowed(vma)))
                 return false;
         /* these checks mirror the abort conditions in vm_normal_page */
         if (vma->vm_flags & VM_MIXEDMAP)
                 return true;
         if (pfn_t_devmap(pfn))
                 return true;
         if (pfn_t_special(pfn))
                 return true;
         if (is_zero_pfn(pfn_t_to_pfn(pfn)))
                 return true;
         return false;
 }
 
 static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma,
                 unsigned long addr, pfn_t pfn, bool mkwrite)
 {
         pgprot_t pgprot = vma->vm_page_prot;
         int err;
 
         if (!vm_mixed_ok(vma, pfn, mkwrite))
                 return VM_FAULT_SIGBUS;
 
         if (addr < vma->vm_start || addr >= vma->vm_end)
                 return VM_FAULT_SIGBUS;
 
         track_pfn_insert(vma, &pgprot, pfn);
 
         if (!pfn_modify_allowed(pfn_t_to_pfn(pfn), pgprot))
                 return VM_FAULT_SIGBUS;
 
         /*
          * If we don't have pte special, then we have to use the pfn_valid()
          * based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must*
          * refcount the page if pfn_valid is true (hence insert_page rather
          * than insert_pfn).  If a zero_pfn were inserted into a VM_MIXEDMAP
          * without pte special, it would there be refcounted as a normal page.
          */
         if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) &&
             !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) {
                 struct page *page;
 
                 /*
                  * At this point we are committed to insert_page()
                  * regardless of whether the caller specified flags that
                  * result in pfn_t_has_page() == false.
                  */
                 page = pfn_to_page(pfn_t_to_pfn(pfn));
                 err = insert_page(vma, addr, page, pgprot);
         } else {
                 return insert_pfn(vma, addr, pfn, pgprot, mkwrite);
         }
 
         if (err == -ENOMEM)
                 return VM_FAULT_OOM;
         if (err < 0 && err != -EBUSY)
                 return VM_FAULT_SIGBUS;
 
         return VM_FAULT_NOPAGE;
 }
 
 vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
                 pfn_t pfn)
 {
         return __vm_insert_mixed(vma, addr, pfn, false);
 }
 EXPORT_SYMBOL(vmf_insert_mixed);
 
 /*
  *  If the insertion of PTE failed because someone else already added a
  *  different entry in the mean time, we treat that as success as we assume
  *  the same entry was actually inserted.
  */
 vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma,
                 unsigned long addr, pfn_t pfn)
 {
         return __vm_insert_mixed(vma, addr, pfn, true);
 }
 
 /*
  * maps a range of physical memory into the requested pages. the old
  * mappings are removed. any references to nonexistent pages results
  * in null mappings (currently treated as "copy-on-access")
  */
 static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
                         unsigned long addr, unsigned long end,
                         unsigned long pfn, pgprot_t prot)
 {
         pte_t *pte, *mapped_pte;
         spinlock_t *ptl;
         int err = 0;
 
         mapped_pte = pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
         if (!pte)
                 return -ENOMEM;
         arch_enter_lazy_mmu_mode();
         do {
                 BUG_ON(!pte_none(ptep_get(pte)));
                 if (!pfn_modify_allowed(pfn, prot)) {
                         err = -EACCES;
                         break;
                 }
                 set_pte_at(mm, addr, pte, pte_mkspecial(pfn_pte(pfn, prot)));
                 pfn++;
         } while (pte++, addr += PAGE_SIZE, addr != end);
         arch_leave_lazy_mmu_mode();
         pte_unmap_unlock(mapped_pte, ptl);
         return err;
 }
 
 static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud,
                         unsigned long addr, unsigned long end,
                         unsigned long pfn, pgprot_t prot)
 {
         pmd_t *pmd;
         unsigned long next;
         int err;
 
         pfn -= addr >> PAGE_SHIFT;
         pmd = pmd_alloc(mm, pud, addr);
         if (!pmd)
                 return -ENOMEM;
         VM_BUG_ON(pmd_trans_huge(*pmd));
         do {
                 next = pmd_addr_end(addr, end);
                 err = remap_pte_range(mm, pmd, addr, next,
                                 pfn + (addr >> PAGE_SHIFT), prot);
                 if (err)
                         return err;
         } while (pmd++, addr = next, addr != end);
         return 0;
 }
 
 static inline int remap_pud_range(struct mm_struct *mm, p4d_t *p4d,
                         unsigned long addr, unsigned long end,
                         unsigned long pfn, pgprot_t prot)
 {
         pud_t *pud;
         unsigned long next;
         int err;
 
         pfn -= addr >> PAGE_SHIFT;
         pud = pud_alloc(mm, p4d, addr);
         if (!pud)
                 return -ENOMEM;
         do {
                 next = pud_addr_end(addr, end);
                 err = remap_pmd_range(mm, pud, addr, next,
                                 pfn + (addr >> PAGE_SHIFT), prot);
                 if (err)
                         return err;
         } while (pud++, addr = next, addr != end);
         return 0;
 }
 
 static inline int remap_p4d_range(struct mm_struct *mm, pgd_t *pgd,
                         unsigned long addr, unsigned long end,
                         unsigned long pfn, pgprot_t prot)
 {
         p4d_t *p4d;
         unsigned long next;
         int err;
 
         pfn -= addr >> PAGE_SHIFT;
         p4d = p4d_alloc(mm, pgd, addr);
         if (!p4d)
                 return -ENOMEM;
         do {
                 next = p4d_addr_end(addr, end);
                 err = remap_pud_range(mm, p4d, addr, next,
                                 pfn + (addr >> PAGE_SHIFT), prot);
                 if (err)
                         return err;
         } while (p4d++, addr = next, addr != end);
         return 0;
 }
 
 static int remap_pfn_range_internal(struct vm_area_struct *vma, unsigned long addr,
                 unsigned long pfn, unsigned long size, pgprot_t prot)
 {
         pgd_t *pgd;
         unsigned long next;
         unsigned long end = addr + PAGE_ALIGN(size);
         struct mm_struct *mm = vma->vm_mm;
         int err;
 
         if (WARN_ON_ONCE(!PAGE_ALIGNED(addr)))
                 return -EINVAL;
 
         /*
          * Physically remapped pages are special. Tell the
          * rest of the world about it:
          *   VM_IO tells people not to look at these pages
          *      (accesses can have side effects).
          *   VM_PFNMAP tells the core MM that the base pages are just
          *      raw PFN mappings, and do not have a "struct page" associated
          *      with them.
          *   VM_DONTEXPAND
          *      Disable vma merging and expanding with mremap().
          *   VM_DONTDUMP
          *      Omit vma from core dump, even when VM_IO turned off.
          *
          * There's a horrible special case to handle copy-on-write
          * behaviour that some programs depend on. We mark the "original"
          * un-COW'ed pages by matching them up with "vma->vm_pgoff".
          * See vm_normal_page() for details.
          */
         if (is_cow_mapping(vma->vm_flags)) {
                 if (addr != vma->vm_start || end != vma->vm_end)
                         return -EINVAL;
                 vma->vm_pgoff = pfn;
         }
 
         vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
 
         BUG_ON(addr >= end);
         pfn -= addr >> PAGE_SHIFT;
         pgd = pgd_offset(mm, addr);
         flush_cache_range(vma, addr, end);
         do {
                 next = pgd_addr_end(addr, end);
                 err = remap_p4d_range(mm, pgd, addr, next,
                                 pfn + (addr >> PAGE_SHIFT), prot);
                 if (err)
                         return err;
         } while (pgd++, addr = next, addr != end);
 
         return 0;
 }
 
 /*
  * Variant of remap_pfn_range that does not call track_pfn_remap.  The caller
  * must have pre-validated the caching bits of the pgprot_t.
  */
 int remap_pfn_range_notrack(struct vm_area_struct *vma, unsigned long addr,
                 unsigned long pfn, unsigned long size, pgprot_t prot)
 {
         int error = remap_pfn_range_internal(vma, addr, pfn, size, prot);
 
         if (!error)
                 return 0;
 
         /*
          * A partial pfn range mapping is dangerous: it does not
          * maintain page reference counts, and callers may free
          * pages due to the error. So zap it early.
          */
         zap_page_range_single(vma, addr, size, NULL);
         return error;
 }
 
 /**
  * remap_pfn_range - remap kernel memory to userspace
  * @vma: user vma to map to
  * @addr: target page aligned user address to start at
  * @pfn: page frame number of kernel physical memory address
  * @size: size of mapping area
  * @prot: page protection flags for this mapping
  *
  * Note: this is only safe if the mm semaphore is held when called.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
                     unsigned long pfn, unsigned long size, pgprot_t prot)
 {
         int err;
 
         err = track_pfn_remap(vma, &prot, pfn, addr, PAGE_ALIGN(size));
         if (err)
                 return -EINVAL;
 
         err = remap_pfn_range_notrack(vma, addr, pfn, size, prot);
         if (err)
                 untrack_pfn(vma, pfn, PAGE_ALIGN(size), true);
         return err;
 }
 EXPORT_SYMBOL(remap_pfn_range);
 
 /**
  * vm_iomap_memory - remap memory to userspace
  * @vma: user vma to map to
  * @start: start of the physical memory to be mapped
  * @len: size of area
  *
  * This is a simplified io_remap_pfn_range() for common driver use. The
  * driver just needs to give us the physical memory range to be mapped,
  * we'll figure out the rest from the vma information.
  *
  * NOTE! Some drivers might want to tweak vma->vm_page_prot first to get
  * whatever write-combining details or similar.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len)
 {
         unsigned long vm_len, pfn, pages;
 
         /* Check that the physical memory area passed in looks valid */
         if (start + len < start)
                 return -EINVAL;
         /*
          * You *really* shouldn't map things that aren't page-aligned,
          * but we've historically allowed it because IO memory might
          * just have smaller alignment.
          */
         len += start & ~PAGE_MASK;
         pfn = start >> PAGE_SHIFT;
         pages = (len + ~PAGE_MASK) >> PAGE_SHIFT;
         if (pfn + pages < pfn)
                 return -EINVAL;
 
         /* We start the mapping 'vm_pgoff' pages into the area */
         if (vma->vm_pgoff > pages)
                 return -EINVAL;
         pfn += vma->vm_pgoff;
         pages -= vma->vm_pgoff;
 
         /* Can we fit all of the mapping? */
         vm_len = vma->vm_end - vma->vm_start;
         if (vm_len >> PAGE_SHIFT > pages)
                 return -EINVAL;
 
         /* Ok, let it rip */
         return io_remap_pfn_range(vma, vma->vm_start, pfn, vm_len, vma->vm_page_prot);
 }
 EXPORT_SYMBOL(vm_iomap_memory);
 
 static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
                                      unsigned long addr, unsigned long end,
                                      pte_fn_t fn, void *data, bool create,
                                      pgtbl_mod_mask *mask)
 {
         pte_t *pte, *mapped_pte;
         int err = 0;
         spinlock_t *ptl;
 
         if (create) {
                 mapped_pte = pte = (mm == &init_mm) ?
                         pte_alloc_kernel_track(pmd, addr, mask) :
                         pte_alloc_map_lock(mm, pmd, addr, &ptl);
                 if (!pte)
                         return -ENOMEM;
         } else {
                 mapped_pte = pte = (mm == &init_mm) ?
                         pte_offset_kernel(pmd, addr) :
                         pte_offset_map_lock(mm, pmd, addr, &ptl);
                 if (!pte)
                         return -EINVAL;
         }
 
         arch_enter_lazy_mmu_mode();
 
         if (fn) {
                 do {
                         if (create || !pte_none(ptep_get(pte))) {
                                 err = fn(pte++, addr, data);
                                 if (err)
                                         break;
                         }
                 } while (addr += PAGE_SIZE, addr != end);
         }
         *mask |= PGTBL_PTE_MODIFIED;
 
         arch_leave_lazy_mmu_mode();
 
         if (mm != &init_mm)
                 pte_unmap_unlock(mapped_pte, ptl);
         return err;
 }
 
 static int apply_to_pmd_range(struct mm_struct *mm, pud_t *pud,
                                      unsigned long addr, unsigned long end,
                                      pte_fn_t fn, void *data, bool create,
                                      pgtbl_mod_mask *mask)
 {
         pmd_t *pmd;
         unsigned long next;
         int err = 0;
 
         BUG_ON(pud_leaf(*pud));
 
         if (create) {
                 pmd = pmd_alloc_track(mm, pud, addr, mask);
                 if (!pmd)
                         return -ENOMEM;
         } else {
                 pmd = pmd_offset(pud, addr);
         }
         do {
                 next = pmd_addr_end(addr, end);
                 if (pmd_none(*pmd) && !create)
                         continue;
                 if (WARN_ON_ONCE(pmd_leaf(*pmd)))
                         return -EINVAL;
                 if (!pmd_none(*pmd) && WARN_ON_ONCE(pmd_bad(*pmd))) {
                         if (!create)
                                 continue;
                         pmd_clear_bad(pmd);
                 }
                 err = apply_to_pte_range(mm, pmd, addr, next,
                                          fn, data, create, mask);
                 if (err)
                         break;
         } while (pmd++, addr = next, addr != end);
 
         return err;
 }
 
 static int apply_to_pud_range(struct mm_struct *mm, p4d_t *p4d,
                                      unsigned long addr, unsigned long end,
                                      pte_fn_t fn, void *data, bool create,
                                      pgtbl_mod_mask *mask)
 {
         pud_t *pud;
         unsigned long next;
         int err = 0;
 
         if (create) {
                 pud = pud_alloc_track(mm, p4d, addr, mask);
                 if (!pud)
                         return -ENOMEM;
         } else {
                 pud = pud_offset(p4d, addr);
         }
         do {
                 next = pud_addr_end(addr, end);
                 if (pud_none(*pud) && !create)
                         continue;
                 if (WARN_ON_ONCE(pud_leaf(*pud)))
                         return -EINVAL;
                 if (!pud_none(*pud) && WARN_ON_ONCE(pud_bad(*pud))) {
                         if (!create)
                                 continue;
                         pud_clear_bad(pud);
                 }
                 err = apply_to_pmd_range(mm, pud, addr, next,
                                          fn, data, create, mask);
                 if (err)
                         break;
         } while (pud++, addr = next, addr != end);
 
         return err;
 }
 
 static int apply_to_p4d_range(struct mm_struct *mm, pgd_t *pgd,
                                      unsigned long addr, unsigned long end,
                                      pte_fn_t fn, void *data, bool create,
                                      pgtbl_mod_mask *mask)
 {
         p4d_t *p4d;
         unsigned long next;
         int err = 0;
 
         if (create) {
                 p4d = p4d_alloc_track(mm, pgd, addr, mask);
                 if (!p4d)
                         return -ENOMEM;
         } else {
                 p4d = p4d_offset(pgd, addr);
         }
         do {
                 next = p4d_addr_end(addr, end);
                 if (p4d_none(*p4d) && !create)
                         continue;
                 if (WARN_ON_ONCE(p4d_leaf(*p4d)))
                         return -EINVAL;
                 if (!p4d_none(*p4d) && WARN_ON_ONCE(p4d_bad(*p4d))) {
                         if (!create)
                                 continue;
                         p4d_clear_bad(p4d);
                 }
                 err = apply_to_pud_range(mm, p4d, addr, next,
                                          fn, data, create, mask);
                 if (err)
                         break;
         } while (p4d++, addr = next, addr != end);
 
         return err;
 }
 
 static int __apply_to_page_range(struct mm_struct *mm, unsigned long addr,
                                  unsigned long size, pte_fn_t fn,
                                  void *data, bool create)
 {
         pgd_t *pgd;
         unsigned long start = addr, next;
         unsigned long end = addr + size;
         pgtbl_mod_mask mask = 0;
         int err = 0;
 
         if (WARN_ON(addr >= end))
                 return -EINVAL;
 
         pgd = pgd_offset(mm, addr);
         do {
                 next = pgd_addr_end(addr, end);
                 if (pgd_none(*pgd) && !create)
                         continue;
                 if (WARN_ON_ONCE(pgd_leaf(*pgd)))
                         return -EINVAL;
                 if (!pgd_none(*pgd) && WARN_ON_ONCE(pgd_bad(*pgd))) {
                         if (!create)
                                 continue;
                         pgd_clear_bad(pgd);
                 }
                 err = apply_to_p4d_range(mm, pgd, addr, next,
                                          fn, data, create, &mask);
                 if (err)
                         break;
         } while (pgd++, addr = next, addr != end);
 
         if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
                 arch_sync_kernel_mappings(start, start + size);
 
         return err;
 }
 
 /*
  * Scan a region of virtual memory, filling in page tables as necessary
  * and calling a provided function on each leaf page table.
  */
 int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
                         unsigned long size, pte_fn_t fn, void *data)
 {
         return __apply_to_page_range(mm, addr, size, fn, data, true);
 }
 EXPORT_SYMBOL_GPL(apply_to_page_range);
 
 /*
  * Scan a region of virtual memory, calling a provided function on
  * each leaf page table where it exists.
  *
  * Unlike apply_to_page_range, this does _not_ fill in page tables
  * where they are absent.
  */
 int apply_to_existing_page_range(struct mm_struct *mm, unsigned long addr,
                                  unsigned long size, pte_fn_t fn, void *data)
 {
         return __apply_to_page_range(mm, addr, size, fn, data, false);
 }
 EXPORT_SYMBOL_GPL(apply_to_existing_page_range);
 
 /*
  * handle_pte_fault chooses page fault handler according to an entry which was
  * read non-atomically.  Before making any commitment, on those architectures
  * or configurations (e.g. i386 with PAE) which might give a mix of unmatched
  * parts, do_swap_page must check under lock before unmapping the pte and
  * proceeding (but do_wp_page is only called after already making such a check;
  * and do_anonymous_page can safely check later on).
  */
 static inline int pte_unmap_same(struct vm_fault *vmf)
 {
         int same = 1;
 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPTION)
         if (sizeof(pte_t) > sizeof(unsigned long)) {
                 spin_lock(vmf->ptl);
                 same = pte_same(ptep_get(vmf->pte), vmf->orig_pte);
                 spin_unlock(vmf->ptl);
         }
 #endif
         pte_unmap(vmf->pte);
         vmf->pte = NULL;
         return same;
 }
 
 /*
  * Return:
  *      0:              copied succeeded
  *      -EHWPOISON:     copy failed due to hwpoison in source page
  *      -EAGAIN:        copied failed (some other reason)
  */
 static inline int __wp_page_copy_user(struct page *dst, struct page *src,
                                       struct vm_fault *vmf)
 {
         int ret;
         void *kaddr;
         void __user *uaddr;
         struct vm_area_struct *vma = vmf->vma;
         struct mm_struct *mm = vma->vm_mm;
         unsigned long addr = vmf->address;
 
         if (likely(src)) {
                 if (copy_mc_user_highpage(dst, src, addr, vma))
                         return -EHWPOISON;
                 return 0;
         }
 
         /*
          * If the source page was a PFN mapping, we don't have
          * a "struct page" for it. We do a best-effort copy by
          * just copying from the original user address. If that
          * fails, we just zero-fill it. Live with it.
          */
         kaddr = kmap_local_page(dst);
         pagefault_disable();
         uaddr = (void __user *)(addr & PAGE_MASK);
 
         /*
          * On architectures with software "accessed" bits, we would
          * take a double page fault, so mark it accessed here.
          */
         vmf->pte = NULL;
         if (!arch_has_hw_pte_young() && !pte_young(vmf->orig_pte)) {
                 pte_t entry;
 
                 vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
                 if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vmf->orig_pte))) {
                         /*
                          * Other thread has already handled the fault
                          * and update local tlb only
                          */
                         if (vmf->pte)
                                 update_mmu_tlb(vma, addr, vmf->pte);
                         ret = -EAGAIN;
                         goto pte_unlock;
                 }
 
                 entry = pte_mkyoung(vmf->orig_pte);
                 if (ptep_set_access_flags(vma, addr, vmf->pte, entry, 0))
                         update_mmu_cache_range(vmf, vma, addr, vmf->pte, 1);
         }
 
         /*
          * This really shouldn't fail, because the page is there
          * in the page tables. But it might just be unreadable,
          * in which case we just give up and fill the result with
          * zeroes.
          */
         if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
                 if (vmf->pte)
                         goto warn;
 
                 /* Re-validate under PTL if the page is still mapped */
                 vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
                 if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vmf->orig_pte))) {
                         /* The PTE changed under us, update local tlb */
                         if (vmf->pte)
                                 update_mmu_tlb(vma, addr, vmf->pte);
                         ret = -EAGAIN;
                         goto pte_unlock;
                 }
 
                 /*
                  * The same page can be mapped back since last copy attempt.
                  * Try to copy again under PTL.
                  */
                 if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
                         /*
                          * Give a warn in case there can be some obscure
                          * use-case
                          */
 warn:
                         WARN_ON_ONCE(1);
                         clear_page(kaddr);
                 }
         }
 
         ret = 0;
 
 pte_unlock:
         if (vmf->pte)
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
         pagefault_enable();
         kunmap_local(kaddr);
         flush_dcache_page(dst);
 
         return ret;
 }
 
 static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma)
 {
         struct file *vm_file = vma->vm_file;
 
         if (vm_file)
                 return mapping_gfp_mask(vm_file->f_mapping) | __GFP_FS | __GFP_IO;
 
         /*
          * Special mappings (e.g. VDSO) do not have any file so fake
          * a default GFP_KERNEL for them.
          */
         return GFP_KERNEL;
 }
 
 /*
  * Notify the address space that the page is about to become writable so that
  * it can prohibit this or wait for the page to get into an appropriate state.
  *
  * We do this without the lock held, so that it can sleep if it needs to.
  */
 static vm_fault_t do_page_mkwrite(struct vm_fault *vmf, struct folio *folio)
 {
         vm_fault_t ret;
         unsigned int old_flags = vmf->flags;
 
         vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
 
         if (vmf->vma->vm_file &&
             IS_SWAPFILE(vmf->vma->vm_file->f_mapping->host))
                 return VM_FAULT_SIGBUS;
 
         ret = vmf->vma->vm_ops->page_mkwrite(vmf);
         /* Restore original flags so that caller is not surprised */
         vmf->flags = old_flags;
         if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
                 return ret;
         if (unlikely(!(ret & VM_FAULT_LOCKED))) {
                 folio_lock(folio);
                 if (!folio->mapping) {
                         folio_unlock(folio);
                         return 0; /* retry */
                 }
                 ret |= VM_FAULT_LOCKED;
         } else
                 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
         return ret;
 }
 
 /*
  * Handle dirtying of a page in shared file mapping on a write fault.
  *
  * The function expects the page to be locked and unlocks it.
  */
 static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         struct address_space *mapping;
         struct folio *folio = page_folio(vmf->page);
         bool dirtied;
         bool page_mkwrite = vma->vm_ops && vma->vm_ops->page_mkwrite;
 
         dirtied = folio_mark_dirty(folio);
         VM_BUG_ON_FOLIO(folio_test_anon(folio), folio);
         /*
          * Take a local copy of the address_space - folio.mapping may be zeroed
          * by truncate after folio_unlock().   The address_space itself remains
          * pinned by vma->vm_file's reference.  We rely on folio_unlock()'s
          * release semantics to prevent the compiler from undoing this copying.
          */
         mapping = folio_raw_mapping(folio);
         folio_unlock(folio);
 
         if (!page_mkwrite)
                 file_update_time(vma->vm_file);
 
         /*
          * Throttle page dirtying rate down to writeback speed.
          *
          * mapping may be NULL here because some device drivers do not
          * set page.mapping but still dirty their pages
          *
          * Drop the mmap_lock before waiting on IO, if we can. The file
          * is pinning the mapping, as per above.
          */
         if ((dirtied || page_mkwrite) && mapping) {
                 struct file *fpin;
 
                 fpin = maybe_unlock_mmap_for_io(vmf, NULL);
                 balance_dirty_pages_ratelimited(mapping);
                 if (fpin) {
                         fput(fpin);
                         return VM_FAULT_COMPLETED;
                 }
         }
 
         return 0;
 }
 
 /*
  * Handle write page faults for pages that can be reused in the current vma
  *
  * This can happen either due to the mapping being with the VM_SHARED flag,
  * or due to us being the last reference standing to the page. In either
  * case, all we need to do here is to mark the page as writable and update
  * any related book-keeping.
  */
 static inline void wp_page_reuse(struct vm_fault *vmf, struct folio *folio)
         __releases(vmf->ptl)
 {
         struct vm_area_struct *vma = vmf->vma;
         pte_t entry;
 
         VM_BUG_ON(!(vmf->flags & FAULT_FLAG_WRITE));
         VM_WARN_ON(is_zero_pfn(pte_pfn(vmf->orig_pte)));
 
         if (folio) {
                 VM_BUG_ON(folio_test_anon(folio) &&
                           !PageAnonExclusive(vmf->page));
                 /*
                  * Clear the folio's cpupid information as the existing
                  * information potentially belongs to a now completely
                  * unrelated process.
                  */
                 folio_xchg_last_cpupid(folio, (1 << LAST_CPUPID_SHIFT) - 1);
         }
 
         flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
         entry = pte_mkyoung(vmf->orig_pte);
         entry = maybe_mkwrite(pte_mkdirty(entry), vma);
         if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
                 update_mmu_cache_range(vmf, vma, vmf->address, vmf->pte, 1);
         pte_unmap_unlock(vmf->pte, vmf->ptl);
         count_vm_event(PGREUSE);
 }
 
 /*
  * We could add a bitflag somewhere, but for now, we know that all
  * vm_ops that have a ->map_pages have been audited and don't need
  * the mmap_lock to be held.
  */
 static inline vm_fault_t vmf_can_call_fault(const struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
 
         if (vma->vm_ops->map_pages || !(vmf->flags & FAULT_FLAG_VMA_LOCK))
                 return 0;
         vma_end_read(vma);
         return VM_FAULT_RETRY;
 }
 
 /**
  * __vmf_anon_prepare - Prepare to handle an anonymous fault.
  * @vmf: The vm_fault descriptor passed from the fault handler.
  *
  * When preparing to insert an anonymous page into a VMA from a
  * fault handler, call this function rather than anon_vma_prepare().
  * If this vma does not already have an associated anon_vma and we are
  * only protected by the per-VMA lock, the caller must retry with the
  * mmap_lock held.  __anon_vma_prepare() will look at adjacent VMAs to
  * determine if this VMA can share its anon_vma, and that's not safe to
  * do with only the per-VMA lock held for this VMA.
  *
  * Return: 0 if fault handling can proceed.  Any other value should be
  * returned to the caller.
  */
 vm_fault_t __vmf_anon_prepare(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         vm_fault_t ret = 0;
 
         if (likely(vma->anon_vma))
                 return 0;
         if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
                 if (!mmap_read_trylock(vma->vm_mm))
                         return VM_FAULT_RETRY;
         }
         if (__anon_vma_prepare(vma))
                 ret = VM_FAULT_OOM;
         if (vmf->flags & FAULT_FLAG_VMA_LOCK)
                 mmap_read_unlock(vma->vm_mm);
         return ret;
 }
 
 /*
  * Handle the case of a page which we actually need to copy to a new page,
  * either due to COW or unsharing.
  *
  * Called with mmap_lock locked and the old page referenced, but
  * without the ptl held.
  *
  * High level logic flow:
  *
  * - Allocate a page, copy the content of the old page to the new one.
  * - Handle book keeping and accounting - cgroups, mmu-notifiers, etc.
  * - Take the PTL. If the pte changed, bail out and release the allocated page
  * - If the pte is still the way we remember it, update the page table and all
  *   relevant references. This includes dropping the reference the page-table
  *   held to the old page, as well as updating the rmap.
  * - In any case, unlock the PTL and drop the reference we took to the old page.
  */
 static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 {
         const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
         struct vm_area_struct *vma = vmf->vma;
         struct mm_struct *mm = vma->vm_mm;
         struct folio *old_folio = NULL;
         struct folio *new_folio = NULL;
         pte_t entry;
         int page_copied = 0;
         struct mmu_notifier_range range;
         vm_fault_t ret;
         bool pfn_is_zero;
 
         delayacct_wpcopy_start();
 
         if (vmf->page)
                 old_folio = page_folio(vmf->page);
         ret = vmf_anon_prepare(vmf);
         if (unlikely(ret))
                 goto out;
 
         pfn_is_zero = is_zero_pfn(pte_pfn(vmf->orig_pte));
         new_folio = folio_prealloc(mm, vma, vmf->address, pfn_is_zero);
         if (!new_folio)
                 goto oom;
 
         if (!pfn_is_zero) {
                 int err;
 
                 err = __wp_page_copy_user(&new_folio->page, vmf->page, vmf);
                 if (err) {
                         /*
                          * COW failed, if the fault was solved by other,
                          * it's fine. If not, userspace would re-fault on
                          * the same address and we will handle the fault
                          * from the second attempt.
                          * The -EHWPOISON case will not be retried.
                          */
                         folio_put(new_folio);
                         if (old_folio)
                                 folio_put(old_folio);
 
                         delayacct_wpcopy_end();
                         return err == -EHWPOISON ? VM_FAULT_HWPOISON : 0;
                 }
                 kmsan_copy_page_meta(&new_folio->page, vmf->page);
         }
 
         __folio_mark_uptodate(new_folio);
 
         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
                                 vmf->address & PAGE_MASK,
                                 (vmf->address & PAGE_MASK) + PAGE_SIZE);
         mmu_notifier_invalidate_range_start(&range);
 
         /*
          * Re-check the pte - we dropped the lock
          */
         vmf->pte = pte_offset_map_lock(mm, vmf->pmd, vmf->address, &vmf->ptl);
         if (likely(vmf->pte && pte_same(ptep_get(vmf->pte), vmf->orig_pte))) {
                 if (old_folio) {
                         if (!folio_test_anon(old_folio)) {
                                 dec_mm_counter(mm, mm_counter_file(old_folio));
                                 inc_mm_counter(mm, MM_ANONPAGES);
                         }
                 } else {
                         ksm_might_unmap_zero_page(mm, vmf->orig_pte);
                         inc_mm_counter(mm, MM_ANONPAGES);
                 }
                 flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
                 entry = mk_pte(&new_folio->page, vma->vm_page_prot);
                 entry = pte_sw_mkyoung(entry);
                 if (unlikely(unshare)) {
                         if (pte_soft_dirty(vmf->orig_pte))
                                 entry = pte_mksoft_dirty(entry);
                         if (pte_uffd_wp(vmf->orig_pte))
                                 entry = pte_mkuffd_wp(entry);
                 } else {
                         entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                 }
 
                 /*
                  * Clear the pte entry and flush it first, before updating the
                  * pte with the new entry, to keep TLBs on different CPUs in
                  * sync. This code used to set the new PTE then flush TLBs, but
                  * that left a window where the new PTE could be loaded into
                  * some TLBs while the old PTE remains in others.
                  */
                 ptep_clear_flush(vma, vmf->address, vmf->pte);
                 folio_add_new_anon_rmap(new_folio, vma, vmf->address, RMAP_EXCLUSIVE);
                 folio_add_lru_vma(new_folio, vma);
                 BUG_ON(unshare && pte_write(entry));
                 set_pte_at(mm, vmf->address, vmf->pte, entry);
                 update_mmu_cache_range(vmf, vma, vmf->address, vmf->pte, 1);
                 if (old_folio) {
                         /*
                          * Only after switching the pte to the new page may
                          * we remove the mapcount here. Otherwise another
                          * process may come and find the rmap count decremented
                          * before the pte is switched to the new page, and
                          * "reuse" the old page writing into it while our pte
                          * here still points into it and can be read by other
                          * threads.
                          *
                          * The critical issue is to order this
                          * folio_remove_rmap_pte() with the ptp_clear_flush
                          * above. Those stores are ordered by (if nothing else,)
                          * the barrier present in the atomic_add_negative
                          * in folio_remove_rmap_pte();
                          *
                          * Then the TLB flush in ptep_clear_flush ensures that
                          * no process can access the old page before the
                          * decremented mapcount is visible. And the old page
                          * cannot be reused until after the decremented
                          * mapcount is visible. So transitively, TLBs to
                          * old page will be flushed before it can be reused.
                          */
                         folio_remove_rmap_pte(old_folio, vmf->page, vma);
                 }
 
                 /* Free the old page.. */
                 new_folio = old_folio;
                 page_copied = 1;
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
         } else if (vmf->pte) {
                 update_mmu_tlb(vma, vmf->address, vmf->pte);
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
         }
 
         mmu_notifier_invalidate_range_end(&range);
 
         if (new_folio)
                 folio_put(new_folio);
         if (old_folio) {
                 if (page_copied)
                         free_swap_cache(old_folio);
                 folio_put(old_folio);
         }
 
         delayacct_wpcopy_end();
         return 0;
 oom:
         ret = VM_FAULT_OOM;
 out:
         if (old_folio)
                 folio_put(old_folio);
 
         delayacct_wpcopy_end();
         return ret;
 }
 
 /**
  * finish_mkwrite_fault - finish page fault for a shared mapping, making PTE
  *                        writeable once the page is prepared
  *
  * @vmf: structure describing the fault
  * @folio: the folio of vmf->page
  *
  * This function handles all that is needed to finish a write page fault in a
  * shared mapping due to PTE being read-only once the mapped page is prepared.
  * It handles locking of PTE and modifying it.
  *
  * The function expects the page to be locked or other protection against
  * concurrent faults / writeback (such as DAX radix tree locks).
  *
  * Return: %0 on success, %VM_FAULT_NOPAGE when PTE got changed before
  * we acquired PTE lock.
  */
 static vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf, struct folio *folio)
 {
         WARN_ON_ONCE(!(vmf->vma->vm_flags & VM_SHARED));
         vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address,
                                        &vmf->ptl);
         if (!vmf->pte)
                 return VM_FAULT_NOPAGE;
         /*
          * We might have raced with another page fault while we released the
          * pte_offset_map_lock.
          */
         if (!pte_same(ptep_get(vmf->pte), vmf->orig_pte)) {
                 update_mmu_tlb(vmf->vma, vmf->address, vmf->pte);
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
                 return VM_FAULT_NOPAGE;
         }
         wp_page_reuse(vmf, folio);
         return 0;
 }
 
 /*
  * Handle write page faults for VM_MIXEDMAP or VM_PFNMAP for a VM_SHARED
  * mapping
  */
 static vm_fault_t wp_pfn_shared(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
 
         if (vma->vm_ops && vma->vm_ops->pfn_mkwrite) {
                 vm_fault_t ret;
 
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
                 ret = vmf_can_call_fault(vmf);
                 if (ret)
                         return ret;
 
                 vmf->flags |= FAULT_FLAG_MKWRITE;
                 ret = vma->vm_ops->pfn_mkwrite(vmf);
                 if (ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))
                         return ret;
                 return finish_mkwrite_fault(vmf, NULL);
         }
         wp_page_reuse(vmf, NULL);
         return 0;
 }
 
 static vm_fault_t wp_page_shared(struct vm_fault *vmf, struct folio *folio)
         __releases(vmf->ptl)
 {
         struct vm_area_struct *vma = vmf->vma;
         vm_fault_t ret = 0;
 
         folio_get(folio);
 
         if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
                 vm_fault_t tmp;
 
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
                 tmp = vmf_can_call_fault(vmf);
                 if (tmp) {
                         folio_put(folio);
                         return tmp;
                 }
 
                 tmp = do_page_mkwrite(vmf, folio);
                 if (unlikely(!tmp || (tmp &
                                       (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
                         folio_put(folio);
                         return tmp;
                 }
                 tmp = finish_mkwrite_fault(vmf, folio);
                 if (unlikely(tmp & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
                         folio_unlock(folio);
                         folio_put(folio);
                         return tmp;
                 }
         } else {
                 wp_page_reuse(vmf, folio);
                 folio_lock(folio);
         }
         ret |= fault_dirty_shared_page(vmf);
         folio_put(folio);
 
         return ret;
 }
 
 static bool wp_can_reuse_anon_folio(struct folio *folio,
                                     struct vm_area_struct *vma)
 {
         /*
          * We could currently only reuse a subpage of a large folio if no
          * other subpages of the large folios are still mapped. However,
          * let's just consistently not reuse subpages even if we could
          * reuse in that scenario, and give back a large folio a bit
          * sooner.
          */
         if (folio_test_large(folio))
                 return false;
 
         /*
          * We have to verify under folio lock: these early checks are
          * just an optimization to avoid locking the folio and freeing
          * the swapcache if there is little hope that we can reuse.
          *
          * KSM doesn't necessarily raise the folio refcount.
          */
         if (folio_test_ksm(folio) || folio_ref_count(folio) > 3)
                 return false;
         if (!folio_test_lru(folio))
                 /*
                  * We cannot easily detect+handle references from
                  * remote LRU caches or references to LRU folios.
                  */
                 lru_add_drain();
         if (folio_ref_count(folio) > 1 + folio_test_swapcache(folio))
                 return false;
         if (!folio_trylock(folio))
                 return false;
         if (folio_test_swapcache(folio))
                 folio_free_swap(folio);
         if (folio_test_ksm(folio) || folio_ref_count(folio) != 1) {
                 folio_unlock(folio);
                 return false;
         }
         /*
          * Ok, we've got the only folio reference from our mapping
          * and the folio is locked, it's dark out, and we're wearing
          * sunglasses. Hit it.
          */
         folio_move_anon_rmap(folio, vma);
         folio_unlock(folio);
         return true;
 }
 
 /*
  * This routine handles present pages, when
  * * users try to write to a shared page (FAULT_FLAG_WRITE)
  * * GUP wants to take a R/O pin on a possibly shared anonymous page
  *   (FAULT_FLAG_UNSHARE)
  *
  * It is done by copying the page to a new address and decrementing the
  * shared-page counter for the old page.
  *
  * Note that this routine assumes that the protection checks have been
  * done by the caller (the low-level page fault routine in most cases).
  * Thus, with FAULT_FLAG_WRITE, we can safely just mark it writable once we've
  * done any necessary COW.
  *
  * In case of FAULT_FLAG_WRITE, we also mark the page dirty at this point even
  * though the page will change only once the write actually happens. This
  * avoids a few races, and potentially makes it more efficient.
  *
  * We enter with non-exclusive mmap_lock (to exclude vma changes,
  * but allow concurrent faults), with pte both mapped and locked.
  * We return with mmap_lock still held, but pte unmapped and unlocked.
  */
 static vm_fault_t do_wp_page(struct vm_fault *vmf)
         __releases(vmf->ptl)
 {
         const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
         struct vm_area_struct *vma = vmf->vma;
         struct folio *folio = NULL;
         pte_t pte;
 
         if (likely(!unshare)) {
                 if (userfaultfd_pte_wp(vma, ptep_get(vmf->pte))) {
                         if (!userfaultfd_wp_async(vma)) {
                                 pte_unmap_unlock(vmf->pte, vmf->ptl);
                                 return handle_userfault(vmf, VM_UFFD_WP);
                         }
 
                         /*
                          * Nothing needed (cache flush, TLB invalidations,
                          * etc.) because we're only removing the uffd-wp bit,
                          * which is completely invisible to the user.
                          */
                         pte = pte_clear_uffd_wp(ptep_get(vmf->pte));
 
                         set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
                         /*
                          * Update this to be prepared for following up CoW
                          * handling
                          */
                         vmf->orig_pte = pte;
                 }
 
                 /*
                  * Userfaultfd write-protect can defer flushes. Ensure the TLB
                  * is flushed in this case before copying.
                  */
                 if (unlikely(userfaultfd_wp(vmf->vma) &&
                              mm_tlb_flush_pending(vmf->vma->vm_mm)))
                         flush_tlb_page(vmf->vma, vmf->address);
         }
 
         vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte);
 
         if (vmf->page)
                 folio = page_folio(vmf->page);
 
         /*
          * Shared mapping: we are guaranteed to have VM_WRITE and
          * FAULT_FLAG_WRITE set at this point.
          */
         if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) {
                 /*
                  * VM_MIXEDMAP !pfn_valid() case, or VM_SOFTDIRTY clear on a
                  * VM_PFNMAP VMA.
                  *
                  * We should not cow pages in a shared writeable mapping.
                  * Just mark the pages writable and/or call ops->pfn_mkwrite.
                  */
                 if (!vmf->page)
                         return wp_pfn_shared(vmf);
                 return wp_page_shared(vmf, folio);
         }
 
         /*
          * Private mapping: create an exclusive anonymous page copy if reuse
          * is impossible. We might miss VM_WRITE for FOLL_FORCE handling.
          *
          * If we encounter a page that is marked exclusive, we must reuse
          * the page without further checks.
          */
         if (folio && folio_test_anon(folio) &&
             (PageAnonExclusive(vmf->page) || wp_can_reuse_anon_folio(folio, vma))) {
                 if (!PageAnonExclusive(vmf->page))
                         SetPageAnonExclusive(vmf->page);
                 if (unlikely(unshare)) {
                         pte_unmap_unlock(vmf->pte, vmf->ptl);
                         return 0;
                 }
                 wp_page_reuse(vmf, folio);
                 return 0;
         }
         /*
          * Ok, we need to copy. Oh, well..
          */
         if (folio)
                 folio_get(folio);
 
         pte_unmap_unlock(vmf->pte, vmf->ptl);
 #ifdef CONFIG_KSM
         if (folio && folio_test_ksm(folio))
                 count_vm_event(COW_KSM);
 #endif
         return wp_page_copy(vmf);
 }
 
 static void unmap_mapping_range_vma(struct vm_area_struct *vma,
                 unsigned long start_addr, unsigned long end_addr,
                 struct zap_details *details)
 {
         zap_page_range_single(vma, start_addr, end_addr - start_addr, details);
 }
 
 static inline void unmap_mapping_range_tree(struct rb_root_cached *root,
                                             pgoff_t first_index,
                                             pgoff_t last_index,
                                             struct zap_details *details)
 {
         struct vm_area_struct *vma;
         pgoff_t vba, vea, zba, zea;
 
         vma_interval_tree_foreach(vma, root, first_index, last_index) {
                 vba = vma->vm_pgoff;
                 vea = vba + vma_pages(vma) - 1;
                 zba = max(first_index, vba);
                 zea = min(last_index, vea);
 
                 unmap_mapping_range_vma(vma,
                         ((zba - vba) << PAGE_SHIFT) + vma->vm_start,
                         ((zea - vba + 1) << PAGE_SHIFT) + vma->vm_start,
                                 details);
         }
 }
 
 /**
  * unmap_mapping_folio() - Unmap single folio from processes.
  * @folio: The locked folio to be unmapped.
  *
  * Unmap this folio from any userspace process which still has it mmaped.
  * Typically, for efficiency, the range of nearby pages has already been
  * unmapped by unmap_mapping_pages() or unmap_mapping_range().  But once
  * truncation or invalidation holds the lock on a folio, it may find that
  * the page has been remapped again: and then uses unmap_mapping_folio()
  * to unmap it finally.
  */
 void unmap_mapping_folio(struct folio *folio)
 {
         struct address_space *mapping = folio->mapping;
         struct zap_details details = { };
         pgoff_t first_index;
         pgoff_t last_index;
 
         VM_BUG_ON(!folio_test_locked(folio));
 
         first_index = folio->index;
         last_index = folio_next_index(folio) - 1;
 
         details.even_cows = false;
         details.single_folio = folio;
         details.zap_flags = ZAP_FLAG_DROP_MARKER;
 
         i_mmap_lock_read(mapping);
         if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
                 unmap_mapping_range_tree(&mapping->i_mmap, first_index,
                                          last_index, &details);
         i_mmap_unlock_read(mapping);
 }
 
 /**
  * unmap_mapping_pages() - Unmap pages from processes.
  * @mapping: The address space containing pages to be unmapped.
  * @start: Index of first page to be unmapped.
  * @nr: Number of pages to be unmapped.  0 to unmap to end of file.
  * @even_cows: Whether to unmap even private COWed pages.
  *
  * Unmap the pages in this address space from any userspace process which
  * has them mmaped.  Generally, you want to remove COWed pages as well when
  * a file is being truncated, but not when invalidating pages from the page
  * cache.
  */
 void unmap_mapping_pages(struct address_space *mapping, pgoff_t start,
                 pgoff_t nr, bool even_cows)
 {
         struct zap_details details = { };
         pgoff_t first_index = start;
         pgoff_t last_index = start + nr - 1;
 
         details.even_cows = even_cows;
         if (last_index < first_index)
                 last_index = ULONG_MAX;
 
         i_mmap_lock_read(mapping);
         if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
                 unmap_mapping_range_tree(&mapping->i_mmap, first_index,
                                          last_index, &details);
         i_mmap_unlock_read(mapping);
 }
 EXPORT_SYMBOL_GPL(unmap_mapping_pages);
 
 /**
  * unmap_mapping_range - unmap the portion of all mmaps in the specified
  * address_space corresponding to the specified byte range in the underlying
  * file.
  *
  * @mapping: the address space containing mmaps to be unmapped.
  * @holebegin: byte in first page to unmap, relative to the start of
  * the underlying file.  This will be rounded down to a PAGE_SIZE
  * boundary.  Note that this is different from truncate_pagecache(), which
  * must keep the partial page.  In contrast, we must get rid of
  * partial pages.
  * @holelen: size of prospective hole in bytes.  This will be rounded
  * up to a PAGE_SIZE boundary.  A holelen of zero truncates to the
  * end of the file.
  * @even_cows: 1 when truncating a file, unmap even private COWed pages;
  * but 0 when invalidating pagecache, don't throw away private data.
  */
 void unmap_mapping_range(struct address_space *mapping,
                 loff_t const holebegin, loff_t const holelen, int even_cows)
 {
         pgoff_t hba = (pgoff_t)(holebegin) >> PAGE_SHIFT;
         pgoff_t hlen = ((pgoff_t)(holelen) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 
         /* Check for overflow. */
         if (sizeof(holelen) > sizeof(hlen)) {
                 long long holeend =
                         (holebegin + holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
                 if (holeend & ~(long long)ULONG_MAX)
                         hlen = ULONG_MAX - hba + 1;
         }
 
         unmap_mapping_pages(mapping, hba, hlen, even_cows);
 }
 EXPORT_SYMBOL(unmap_mapping_range);
 
 /*
  * Restore a potential device exclusive pte to a working pte entry
  */
 static vm_fault_t remove_device_exclusive_entry(struct vm_fault *vmf)
 {
         struct folio *folio = page_folio(vmf->page);
         struct vm_area_struct *vma = vmf->vma;
         struct mmu_notifier_range range;
         vm_fault_t ret;
 
         /*
          * We need a reference to lock the folio because we don't hold
          * the PTL so a racing thread can remove the device-exclusive
          * entry and unmap it. If the folio is free the entry must
          * have been removed already. If it happens to have already
          * been re-allocated after being freed all we do is lock and
          * unlock it.
          */
         if (!folio_try_get(folio))
                 return 0;
 
         ret = folio_lock_or_retry(folio, vmf);
         if (ret) {
                 folio_put(folio);
                 return ret;
         }
         mmu_notifier_range_init_owner(&range, MMU_NOTIFY_EXCLUSIVE, 0,
                                 vma->vm_mm, vmf->address & PAGE_MASK,
                                 (vmf->address & PAGE_MASK) + PAGE_SIZE, NULL);
         mmu_notifier_invalidate_range_start(&range);
 
         vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
                                 &vmf->ptl);
         if (likely(vmf->pte && pte_same(ptep_get(vmf->pte), vmf->orig_pte)))
                 restore_exclusive_pte(vma, vmf->page, vmf->address, vmf->pte);
 
         if (vmf->pte)
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
         folio_unlock(folio);
         folio_put(folio);
 
         mmu_notifier_invalidate_range_end(&range);
         return 0;
 }
 
 static inline bool should_try_to_free_swap(struct folio *folio,
                                            struct vm_area_struct *vma,
                                            unsigned int fault_flags)
 {
         if (!folio_test_swapcache(folio))
                 return false;
         if (mem_cgroup_swap_full(folio) || (vma->vm_flags & VM_LOCKED) ||
             folio_test_mlocked(folio))
                 return true;
         /*
          * If we want to map a page that's in the swapcache writable, we
          * have to detect via the refcount if we're really the exclusive
          * user. Try freeing the swapcache to get rid of the swapcache
          * reference only in case it's likely that we'll be the exlusive user.
          */
         return (fault_flags & FAULT_FLAG_WRITE) && !folio_test_ksm(folio) &&
                 folio_ref_count(folio) == (1 + folio_nr_pages(folio));
 }
 
 static vm_fault_t pte_marker_clear(struct vm_fault *vmf)
 {
         vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
                                        vmf->address, &vmf->ptl);
         if (!vmf->pte)
                 return 0;
         /*
          * Be careful so that we will only recover a special uffd-wp pte into a
          * none pte.  Otherwise it means the pte could have changed, so retry.
          *
          * This should also cover the case where e.g. the pte changed
          * quickly from a PTE_MARKER_UFFD_WP into PTE_MARKER_POISONED.
          * So is_pte_marker() check is not enough to safely drop the pte.
          */
         if (pte_same(vmf->orig_pte, ptep_get(vmf->pte)))
                 pte_clear(vmf->vma->vm_mm, vmf->address, vmf->pte);
         pte_unmap_unlock(vmf->pte, vmf->ptl);
         return 0;
 }
 
 static vm_fault_t do_pte_missing(struct vm_fault *vmf)
 {
         if (vma_is_anonymous(vmf->vma))
                 return do_anonymous_page(vmf);
         else
                 return do_fault(vmf);
 }
 
 /*
  * This is actually a page-missing access, but with uffd-wp special pte
  * installed.  It means this pte was wr-protected before being unmapped.
  */
 static vm_fault_t pte_marker_handle_uffd_wp(struct vm_fault *vmf)
 {
         /*
          * Just in case there're leftover special ptes even after the region
          * got unregistered - we can simply clear them.
          */
         if (unlikely(!userfaultfd_wp(vmf->vma)))
                 return pte_marker_clear(vmf);
 
         return do_pte_missing(vmf);
 }
 
 static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
 {
         swp_entry_t entry = pte_to_swp_entry(vmf->orig_pte);
         unsigned long marker = pte_marker_get(entry);
 
         /*
          * PTE markers should never be empty.  If anything weird happened,
          * the best thing to do is to kill the process along with its mm.
          */
         if (WARN_ON_ONCE(!marker))
                 return VM_FAULT_SIGBUS;
 
         /* Higher priority than uffd-wp when data corrupted */
         if (marker & PTE_MARKER_POISONED)
                 return VM_FAULT_HWPOISON;
 
         if (pte_marker_entry_uffd_wp(entry))
                 return pte_marker_handle_uffd_wp(vmf);
 
         /* This is an unknown pte marker */
         return VM_FAULT_SIGBUS;
 }
 
 /*
  * We enter with non-exclusive mmap_lock (to exclude vma changes,
  * but allow concurrent faults), and pte mapped but not yet locked.
  * We return with pte unmapped and unlocked.
  *
  * We return with the mmap_lock locked or unlocked in the same cases
  * as does filemap_fault().
  */
 vm_fault_t do_swap_page(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         struct folio *swapcache, *folio = NULL;
         struct page *page;
         struct swap_info_struct *si = NULL;
         rmap_t rmap_flags = RMAP_NONE;
         bool need_clear_cache = false;
         bool exclusive = false;
         swp_entry_t entry;
         pte_t pte;
         vm_fault_t ret = 0;
         void *shadow = NULL;
         int nr_pages;
         unsigned long page_idx;
         unsigned long address;
         pte_t *ptep;
 
         if (!pte_unmap_same(vmf))
                 goto out;
 
         entry = pte_to_swp_entry(vmf->orig_pte);
         if (unlikely(non_swap_entry(entry))) {
                 if (is_migration_entry(entry)) {
                         migration_entry_wait(vma->vm_mm, vmf->pmd,
                                              vmf->address);
                 } else if (is_device_exclusive_entry(entry)) {
                         vmf->page = pfn_swap_entry_to_page(entry);
                         ret = remove_device_exclusive_entry(vmf);
                 } else if (is_device_private_entry(entry)) {
                         if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
                                 /*
                                  * migrate_to_ram is not yet ready to operate
                                  * under VMA lock.
                                  */
                                 vma_end_read(vma);
                                 ret = VM_FAULT_RETRY;
                                 goto out;
                         }
 
                         vmf->page = pfn_swap_entry_to_page(entry);
                         vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
                                         vmf->address, &vmf->ptl);
                         if (unlikely(!vmf->pte ||
                                      !pte_same(ptep_get(vmf->pte),
                                                         vmf->orig_pte)))
                                 goto unlock;
 
                         /*
                          * Get a page reference while we know the page can't be
                          * freed.
                          */
                         get_page(vmf->page);
                         pte_unmap_unlock(vmf->pte, vmf->ptl);
                         ret = vmf->page->pgmap->ops->migrate_to_ram(vmf);
                         put_page(vmf->page);
                 } else if (is_hwpoison_entry(entry)) {
                         ret = VM_FAULT_HWPOISON;
                 } else if (is_pte_marker_entry(entry)) {
                         ret = handle_pte_marker(vmf);
                 } else {
                         print_bad_pte(vma, vmf->address, vmf->orig_pte, NULL);
                         ret = VM_FAULT_SIGBUS;
                 }
                 goto out;
         }
 
         /* Prevent swapoff from happening to us. */
         si = get_swap_device(entry);
         if (unlikely(!si))
                 goto out;
 
         folio = swap_cache_get_folio(entry, vma, vmf->address);
         if (folio)
                 page = folio_file_page(folio, swp_offset(entry));
         swapcache = folio;
 
         if (!folio) {
                 if (data_race(si->flags & SWP_SYNCHRONOUS_IO) &&
                     __swap_count(entry) == 1) {
                         /*
                          * Prevent parallel swapin from proceeding with
                          * the cache flag. Otherwise, another thread may
                          * finish swapin first, free the entry, and swapout
                          * reusing the same entry. It's undetectable as
                          * pte_same() returns true due to entry reuse.
                          */
                         if (swapcache_prepare(entry)) {
                                 /* Relax a bit to prevent rapid repeated page faults */
                                 schedule_timeout_uninterruptible(1);
                                 goto out;
                         }
                         need_clear_cache = true;
 
                         /* skip swapcache */
                         folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0,
                                                 vma, vmf->address, false);
                         page = &folio->page;
                         if (folio) {
                                 __folio_set_locked(folio);
                                 __folio_set_swapbacked(folio);
 
                                 if (mem_cgroup_swapin_charge_folio(folio,
                                                         vma->vm_mm, GFP_KERNEL,
                                                         entry)) {
                                         ret = VM_FAULT_OOM;
                                         goto out_page;
                                 }
                                 mem_cgroup_swapin_uncharge_swap(entry);
 
                                 shadow = get_shadow_from_swap_cache(entry);
                                 if (shadow)
                                         workingset_refault(folio, shadow);
 
                                 folio_add_lru(folio);
 
                                 /* To provide entry to swap_read_folio() */
                                 folio->swap = entry;
                                 swap_read_folio(folio, NULL);
                                 folio->private = NULL;
                         }
                 } else {
                         page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
                                                 vmf);
                         if (page)
                                 folio = page_folio(page);
                         swapcache = folio;
                 }
 
                 if (!folio) {
                         /*
                          * Back out if somebody else faulted in this pte
                          * while we released the pte lock.
                          */
                         vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
                                         vmf->address, &vmf->ptl);
                         if (likely(vmf->pte &&
                                    pte_same(ptep_get(vmf->pte), vmf->orig_pte)))
                                 ret = VM_FAULT_OOM;
                         goto unlock;
                 }
 
                 /* Had to read the page from swap area: Major fault */
                 ret = VM_FAULT_MAJOR;
                 count_vm_event(PGMAJFAULT);
                 count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
         } else if (PageHWPoison(page)) {
                 /*
                  * hwpoisoned dirty swapcache pages are kept for killing
                  * owner processes (which may be unknown at hwpoison time)
                  */
                 ret = VM_FAULT_HWPOISON;
                 goto out_release;
         }
 
         ret |= folio_lock_or_retry(folio, vmf);
         if (ret & VM_FAULT_RETRY)
                 goto out_release;
 
         if (swapcache) {
                 /*
                  * Make sure folio_free_swap() or swapoff did not release the
                  * swapcache from under us.  The page pin, and pte_same test
                  * below, are not enough to exclude that.  Even if it is still
                  * swapcache, we need to check that the page's swap has not
                  * changed.
                  */
                 if (unlikely(!folio_test_swapcache(folio) ||
                              page_swap_entry(page).val != entry.val))
                         goto out_page;
 
                 /*
                  * KSM sometimes has to copy on read faults, for example, if
                  * page->index of !PageKSM() pages would be nonlinear inside the
                  * anon VMA -- PageKSM() is lost on actual swapout.
                  */
                 folio = ksm_might_need_to_copy(folio, vma, vmf->address);
                 if (unlikely(!folio)) {
                         ret = VM_FAULT_OOM;
                         folio = swapcache;
                         goto out_page;
                 } else if (unlikely(folio == ERR_PTR(-EHWPOISON))) {
                         ret = VM_FAULT_HWPOISON;
                         folio = swapcache;
                         goto out_page;
                 }
                 if (folio != swapcache)
                         page = folio_page(folio, 0);
 
                 /*
                  * If we want to map a page that's in the swapcache writable, we
                  * have to detect via the refcount if we're really the exclusive
                  * owner. Try removing the extra reference from the local LRU
                  * caches if required.
                  */
                 if ((vmf->flags & FAULT_FLAG_WRITE) && folio == swapcache &&
                     !folio_test_ksm(folio) && !folio_test_lru(folio))
                         lru_add_drain();
         }
 
         folio_throttle_swaprate(folio, GFP_KERNEL);
 
         /*
          * Back out if somebody else already faulted in this pte.
          */
         vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
                         &vmf->ptl);
         if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vmf->orig_pte)))
                 goto out_nomap;
 
         if (unlikely(!folio_test_uptodate(folio))) {
                 ret = VM_FAULT_SIGBUS;
                 goto out_nomap;
         }
 
         nr_pages = 1;
         page_idx = 0;
         address = vmf->address;
         ptep = vmf->pte;
         if (folio_test_large(folio) && folio_test_swapcache(folio)) {
                 int nr = folio_nr_pages(folio);
                 unsigned long idx = folio_page_idx(folio, page);
                 unsigned long folio_start = address - idx * PAGE_SIZE;
                 unsigned long folio_end = folio_start + nr * PAGE_SIZE;
                 pte_t *folio_ptep;
                 pte_t folio_pte;
 
                 if (unlikely(folio_start < max(address & PMD_MASK, vma->vm_start)))
                         goto check_folio;
                 if (unlikely(folio_end > pmd_addr_end(address, vma->vm_end)))
                         goto check_folio;
 
                 folio_ptep = vmf->pte - idx;
                 folio_pte = ptep_get(folio_ptep);
                 if (!pte_same(folio_pte, pte_move_swp_offset(vmf->orig_pte, -idx)) ||
                     swap_pte_batch(folio_ptep, nr, folio_pte) != nr)
                         goto check_folio;
 
                 page_idx = idx;
                 address = folio_start;
                 ptep = folio_ptep;
                 nr_pages = nr;
                 entry = folio->swap;
                 page = &folio->page;
         }
 
 check_folio:
         /*
          * PG_anon_exclusive reuses PG_mappedtodisk for anon pages. A swap pte
          * must never point at an anonymous page in the swapcache that is
          * PG_anon_exclusive. Sanity check that this holds and especially, that
          * no filesystem set PG_mappedtodisk on a page in the swapcache. Sanity
          * check after taking the PT lock and making sure that nobody
          * concurrently faulted in this page and set PG_anon_exclusive.
          */
         BUG_ON(!folio_test_anon(folio) && folio_test_mappedtodisk(folio));
         BUG_ON(folio_test_anon(folio) && PageAnonExclusive(page));
 
         /*
          * Check under PT lock (to protect against concurrent fork() sharing
          * the swap entry concurrently) for certainly exclusive pages.
          */
         if (!folio_test_ksm(folio)) {
                 exclusive = pte_swp_exclusive(vmf->orig_pte);
                 if (folio != swapcache) {
                         /*
                          * We have a fresh page that is not exposed to the
                          * swapcache -> certainly exclusive.
                          */
                         exclusive = true;
                 } else if (exclusive && folio_test_writeback(folio) &&
                           data_race(si->flags & SWP_STABLE_WRITES)) {
                         /*
                          * This is tricky: not all swap backends support
                          * concurrent page modifications while under writeback.
                          *
                          * So if we stumble over such a page in the swapcache
                          * we must not set the page exclusive, otherwise we can
                          * map it writable without further checks and modify it
                          * while still under writeback.
                          *
                          * For these problematic swap backends, simply drop the
                          * exclusive marker: this is perfectly fine as we start
                          * writeback only if we fully unmapped the page and
                          * there are no unexpected references on the page after
                          * unmapping succeeded. After fully unmapped, no
                          * further GUP references (FOLL_GET and FOLL_PIN) can
                          * appear, so dropping the exclusive marker and mapping
                          * it only R/O is fine.
                          */
                         exclusive = false;
                 }
         }
 
         /*
          * Some architectures may have to restore extra metadata to the page
          * when reading from swap. This metadata may be indexed by swap entry
          * so this must be called before swap_free().
          */
         arch_swap_restore(folio_swap(entry, folio), folio);
 
         /*
          * Remove the swap entry and conditionally try to free up the swapcache.
          * We're already holding a reference on the page but haven't mapped it
          * yet.
          */
         swap_free_nr(entry, nr_pages);
         if (should_try_to_free_swap(folio, vma, vmf->flags))
                 folio_free_swap(folio);
 
         add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages);
         add_mm_counter(vma->vm_mm, MM_SWAPENTS, -nr_pages);
         pte = mk_pte(page, vma->vm_page_prot);
         if (pte_swp_soft_dirty(vmf->orig_pte))
                 pte = pte_mksoft_dirty(pte);
         if (pte_swp_uffd_wp(vmf->orig_pte))
                 pte = pte_mkuffd_wp(pte);
 
         /*
          * Same logic as in do_wp_page(); however, optimize for pages that are
          * certainly not shared either because we just allocated them without
          * exposing them to the swapcache or because the swap entry indicates
          * exclusivity.
          */
         if (!folio_test_ksm(folio) &&
             (exclusive || folio_ref_count(folio) == 1)) {
                 if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
                     !pte_needs_soft_dirty_wp(vma, pte)) {
                         pte = pte_mkwrite(pte, vma);
                         if (vmf->flags & FAULT_FLAG_WRITE) {
                                 pte = pte_mkdirty(pte);
                                 vmf->flags &= ~FAULT_FLAG_WRITE;
                         }
                 }
                 rmap_flags |= RMAP_EXCLUSIVE;
         }
         folio_ref_add(folio, nr_pages - 1);
         flush_icache_pages(vma, page, nr_pages);
         vmf->orig_pte = pte_advance_pfn(pte, page_idx);
 
         /* ksm created a completely new copy */
         if (unlikely(folio != swapcache && swapcache)) {
                 folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE);
                 folio_add_lru_vma(folio, vma);
         } else if (!folio_test_anon(folio)) {
                 /*
                  * We currently only expect small !anon folios, which are either
                  * fully exclusive or fully shared. If we ever get large folios
                  * here, we have to be careful.
                  */
                 VM_WARN_ON_ONCE(folio_test_large(folio));
                 VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
                 folio_add_new_anon_rmap(folio, vma, address, rmap_flags);
         } else {
                 folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, address,
                                         rmap_flags);
         }
 
         VM_BUG_ON(!folio_test_anon(folio) ||
                         (pte_write(pte) && !PageAnonExclusive(page)));
         set_ptes(vma->vm_mm, address, ptep, pte, nr_pages);
         arch_do_swap_page_nr(vma->vm_mm, vma, address,
                         pte, pte, nr_pages);
 
         folio_unlock(folio);
         if (folio != swapcache && swapcache) {
                 /*
                  * Hold the lock to avoid the swap entry to be reused
                  * until we take the PT lock for the pte_same() check
                  * (to avoid false positives from pte_same). For
                  * further safety release the lock after the swap_free
                  * so that the swap count won't change under a
                  * parallel locked swapcache.
                  */
                 folio_unlock(swapcache);
                 folio_put(swapcache);
         }
 
         if (vmf->flags & FAULT_FLAG_WRITE) {
                 ret |= do_wp_page(vmf);
                 if (ret & VM_FAULT_ERROR)
                         ret &= VM_FAULT_ERROR;
                 goto out;
         }
 
         /* No need to invalidate - it was non-present before */
         update_mmu_cache_range(vmf, vma, address, ptep, nr_pages);
 unlock:
         if (vmf->pte)
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
 out:
         /* Clear the swap cache pin for direct swapin after PTL unlock */
         if (need_clear_cache)
                 swapcache_clear(si, entry);
         if (si)
                 put_swap_device(si);
         return ret;
 out_nomap:
         if (vmf->pte)
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
 out_page:
         folio_unlock(folio);
 out_release:
         folio_put(folio);
         if (folio != swapcache && swapcache) {
                 folio_unlock(swapcache);
                 folio_put(swapcache);
         }
         if (need_clear_cache)
                 swapcache_clear(si, entry);
         if (si)
                 put_swap_device(si);
         return ret;
 }
 
 static bool pte_range_none(pte_t *pte, int nr_pages)
 {
         int i;
 
         for (i = 0; i < nr_pages; i++) {
                 if (!pte_none(ptep_get_lockless(pte + i)))
                         return false;
         }
 
         return true;
 }
 
 static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
         unsigned long orders;
         struct folio *folio;
         unsigned long addr;
         pte_t *pte;
         gfp_t gfp;
         int order;
 
         /*
          * If uffd is active for the vma we need per-page fault fidelity to
          * maintain the uffd semantics.
          */
         if (unlikely(userfaultfd_armed(vma)))
                 goto fallback;
 
         /*
          * Get a list of all the (large) orders below PMD_ORDER that are enabled
          * for this vma. Then filter out the orders that can't be allocated over
          * the faulting address and still be fully contained in the vma.
          */
         orders = thp_vma_allowable_orders(vma, vma->vm_flags,
                         TVA_IN_PF | TVA_ENFORCE_SYSFS, BIT(PMD_ORDER) - 1);
         orders = thp_vma_suitable_orders(vma, vmf->address, orders);
 
         if (!orders)
                 goto fallback;
 
         pte = pte_offset_map(vmf->pmd, vmf->address & PMD_MASK);
         if (!pte)
                 return ERR_PTR(-EAGAIN);
 
         /*
          * Find the highest order where the aligned range is completely
          * pte_none(). Note that all remaining orders will be completely
          * pte_none().
          */
         order = highest_order(orders);
         while (orders) {
                 addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
                 if (pte_range_none(pte + pte_index(addr), 1 << order))
                         break;
                 order = next_order(&orders, order);
         }
 
         pte_unmap(pte);
 
         if (!orders)
                 goto fallback;
 
         /* Try allocating the highest of the remaining orders. */
         gfp = vma_thp_gfp_mask(vma);
         while (orders) {
                 addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
                 folio = vma_alloc_folio(gfp, order, vma, addr, true);
                 if (folio) {
                         if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
                                 count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
                                 folio_put(folio);
                                 goto next;
                         }
                         folio_throttle_swaprate(folio, gfp);
                         folio_zero_user(folio, vmf->address);
                         return folio;
                 }
 next:
                 count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
                 order = next_order(&orders, order);
         }
 
 fallback:
 #endif
         return folio_prealloc(vma->vm_mm, vma, vmf->address, true);
 }
 
 /*
  * We enter with non-exclusive mmap_lock (to exclude vma changes,
  * but allow concurrent faults), and pte mapped but not yet locked.
  * We return with mmap_lock still held, but pte unmapped and unlocked.
  */
 static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         unsigned long addr = vmf->address;
         struct folio *folio;
         vm_fault_t ret = 0;
         int nr_pages = 1;
         pte_t entry;
 
         /* File mapping without ->vm_ops ? */
         if (vma->vm_flags & VM_SHARED)
                 return VM_FAULT_SIGBUS;
 
         /*
          * Use pte_alloc() instead of pte_alloc_map(), so that OOM can
          * be distinguished from a transient failure of pte_offset_map().
          */
         if (pte_alloc(vma->vm_mm, vmf->pmd))
                 return VM_FAULT_OOM;
 
         /* Use the zero-page for reads */
         if (!(vmf->flags & FAULT_FLAG_WRITE) &&
                         !mm_forbids_zeropage(vma->vm_mm)) {
                 entry = pte_mkspecial(pfn_pte(my_zero_pfn(vmf->address),
                                                 vma->vm_page_prot));
                 vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
                                 vmf->address, &vmf->ptl);
                 if (!vmf->pte)
                         goto unlock;
                 if (vmf_pte_changed(vmf)) {
                         update_mmu_tlb(vma, vmf->address, vmf->pte);
                         goto unlock;
                 }
                 ret = check_stable_address_space(vma->vm_mm);
                 if (ret)
                         goto unlock;
                 /* Deliver the page fault to userland, check inside PT lock */
                 if (userfaultfd_missing(vma)) {
                         pte_unmap_unlock(vmf->pte, vmf->ptl);
                         return handle_userfault(vmf, VM_UFFD_MISSING);
                 }
                 goto setpte;
         }
 
         /* Allocate our own private page. */
         ret = vmf_anon_prepare(vmf);
         if (ret)
                 return ret;
         /* Returns NULL on OOM or ERR_PTR(-EAGAIN) if we must retry the fault */
         folio = alloc_anon_folio(vmf);
         if (IS_ERR(folio))
                 return 0;
         if (!folio)
                 goto oom;
 
         nr_pages = folio_nr_pages(folio);
         addr = ALIGN_DOWN(vmf->address, nr_pages * PAGE_SIZE);
 
         /*
          * The memory barrier inside __folio_mark_uptodate makes sure that
          * preceding stores to the page contents become visible before
          * the set_pte_at() write.
          */
         __folio_mark_uptodate(folio);
 
         entry = mk_pte(&folio->page, vma->vm_page_prot);
         entry = pte_sw_mkyoung(entry);
         if (vma->vm_flags & VM_WRITE)
                 entry = pte_mkwrite(pte_mkdirty(entry), vma);
 
         vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl);
         if (!vmf->pte)
                 goto release;
         if (nr_pages == 1 && vmf_pte_changed(vmf)) {
                 update_mmu_tlb(vma, addr, vmf->pte);
                 goto release;
         } else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
                 update_mmu_tlb_range(vma, addr, vmf->pte, nr_pages);
                 goto release;
         }
 
         ret = check_stable_address_space(vma->vm_mm);
         if (ret)
                 goto release;
 
         /* Deliver the page fault to userland, check inside PT lock */
         if (userfaultfd_missing(vma)) {
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
                 folio_put(folio);
                 return handle_userfault(vmf, VM_UFFD_MISSING);
         }
 
         folio_ref_add(folio, nr_pages - 1);
         add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages);
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
         count_mthp_stat(folio_order(folio), MTHP_STAT_ANON_FAULT_ALLOC);
 #endif
         folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE);
         folio_add_lru_vma(folio, vma);
 setpte:
         if (vmf_orig_pte_uffd_wp(vmf))
                 entry = pte_mkuffd_wp(entry);
         set_ptes(vma->vm_mm, addr, vmf->pte, entry, nr_pages);
 
         /* No need to invalidate - it was non-present before */
         update_mmu_cache_range(vmf, vma, addr, vmf->pte, nr_pages);
 unlock:
         if (vmf->pte)
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
         return ret;
 release:
         folio_put(folio);
         goto unlock;
 oom:
         return VM_FAULT_OOM;
 }
 
 /*
  * The mmap_lock must have been held on entry, and may have been
  * released depending on flags and vma->vm_ops->fault() return value.
  * See filemap_fault() and __lock_page_retry().
  */
 static vm_fault_t __do_fault(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         struct folio *folio;
         vm_fault_t ret;
 
         /*
          * Preallocate pte before we take page_lock because this might lead to
          * deadlocks for memcg reclaim which waits for pages under writeback:
          *                              lock_page(A)
          *                              SetPageWriteback(A)
          *                              unlock_page(A)
          * lock_page(B)
          *                              lock_page(B)
          * pte_alloc_one
          *   shrink_folio_list
          *     wait_on_page_writeback(A)
          *                              SetPageWriteback(B)
          *                              unlock_page(B)
          *                              # flush A, B to clear the writeback
          */
         if (pmd_none(*vmf->pmd) && !vmf->prealloc_pte) {
                 vmf->prealloc_pte = pte_alloc_one(vma->vm_mm);
                 if (!vmf->prealloc_pte)
                         return VM_FAULT_OOM;
         }
 
         ret = vma->vm_ops->fault(vmf);
         if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY |
                             VM_FAULT_DONE_COW)))
                 return ret;
 
         folio = page_folio(vmf->page);
         if (unlikely(PageHWPoison(vmf->page))) {
                 vm_fault_t poisonret = VM_FAULT_HWPOISON;
                 if (ret & VM_FAULT_LOCKED) {
                         if (page_mapped(vmf->page))
                                 unmap_mapping_folio(folio);
                         /* Retry if a clean folio was removed from the cache. */
                         if (mapping_evict_folio(folio->mapping, folio))
                                 poisonret = VM_FAULT_NOPAGE;
                         folio_unlock(folio);
                 }
                 folio_put(folio);
                 vmf->page = NULL;
                 return poisonret;
         }
 
         if (unlikely(!(ret & VM_FAULT_LOCKED)))
                 folio_lock(folio);
         else
                 VM_BUG_ON_PAGE(!folio_test_locked(folio), vmf->page);
 
         return ret;
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static void deposit_prealloc_pte(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
 
         pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, vmf->prealloc_pte);
         /*
          * We are going to consume the prealloc table,
          * count that as nr_ptes.
          */
         mm_inc_nr_ptes(vma->vm_mm);
         vmf->prealloc_pte = NULL;
 }
 
 vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
 {
         struct folio *folio = page_folio(page);
         struct vm_area_struct *vma = vmf->vma;
         bool write = vmf->flags & FAULT_FLAG_WRITE;
         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
         pmd_t entry;
         vm_fault_t ret = VM_FAULT_FALLBACK;
 
         if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER))
                 return ret;
 
         if (folio_order(folio) != HPAGE_PMD_ORDER)
                 return ret;
         page = &folio->page;
 
         /*
          * Just backoff if any subpage of a THP is corrupted otherwise
          * the corrupted page may mapped by PMD silently to escape the
          * check.  This kind of THP just can be PTE mapped.  Access to
          * the corrupted subpage should trigger SIGBUS as expected.
          */
         if (unlikely(folio_test_has_hwpoisoned(folio)))
                 return ret;
 
         /*
          * Archs like ppc64 need additional space to store information
          * related to pte entry. Use the preallocated table for that.
          */
         if (arch_needs_pgtable_deposit() && !vmf->prealloc_pte) {
                 vmf->prealloc_pte = pte_alloc_one(vma->vm_mm);
                 if (!vmf->prealloc_pte)
                         return VM_FAULT_OOM;
         }
 
         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
         if (unlikely(!pmd_none(*vmf->pmd)))
                 goto out;
 
         flush_icache_pages(vma, page, HPAGE_PMD_NR);
 
         entry = mk_huge_pmd(page, vma->vm_page_prot);
         if (write)
                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 
         add_mm_counter(vma->vm_mm, mm_counter_file(folio), HPAGE_PMD_NR);
         folio_add_file_rmap_pmd(folio, page, vma);
 
         /*
          * deposit and withdraw with pmd lock held
          */
         if (arch_needs_pgtable_deposit())
                 deposit_prealloc_pte(vmf);
 
         set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
 
         update_mmu_cache_pmd(vma, haddr, vmf->pmd);
 
         /* fault is handled */
         ret = 0;
         count_vm_event(THP_FILE_MAPPED);
 out:
         spin_unlock(vmf->ptl);
         return ret;
 }
 #else
 vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
 {
         return VM_FAULT_FALLBACK;
 }
 #endif
 
 /**
  * set_pte_range - Set a range of PTEs to point to pages in a folio.
  * @vmf: Fault decription.
  * @folio: The folio that contains @page.
  * @page: The first page to create a PTE for.
  * @nr: The number of PTEs to create.
  * @addr: The first address to create a PTE for.
  */
 void set_pte_range(struct vm_fault *vmf, struct folio *folio,
                 struct page *page, unsigned int nr, unsigned long addr)
 {
         struct vm_area_struct *vma = vmf->vma;
         bool write = vmf->flags & FAULT_FLAG_WRITE;
         bool prefault = !in_range(vmf->address, addr, nr * PAGE_SIZE);
         pte_t entry;
 
         flush_icache_pages(vma, page, nr);
         entry = mk_pte(page, vma->vm_page_prot);
 
         if (prefault && arch_wants_old_prefaulted_pte())
                 entry = pte_mkold(entry);
         else
                 entry = pte_sw_mkyoung(entry);
 
         if (write)
                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
         if (unlikely(vmf_orig_pte_uffd_wp(vmf)))
                 entry = pte_mkuffd_wp(entry);
         /* copy-on-write page */
         if (write && !(vma->vm_flags & VM_SHARED)) {
                 VM_BUG_ON_FOLIO(nr != 1, folio);
                 folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE);
                 folio_add_lru_vma(folio, vma);
         } else {
                 folio_add_file_rmap_ptes(folio, page, nr, vma);
         }
         set_ptes(vma->vm_mm, addr, vmf->pte, entry, nr);
 
         /* no need to invalidate: a not-present page won't be cached */
         update_mmu_cache_range(vmf, vma, addr, vmf->pte, nr);
 }
 
 static bool vmf_pte_changed(struct vm_fault *vmf)
 {
         if (vmf->flags & FAULT_FLAG_ORIG_PTE_VALID)
                 return !pte_same(ptep_get(vmf->pte), vmf->orig_pte);
 
         return !pte_none(ptep_get(vmf->pte));
 }
 
 /**
  * finish_fault - finish page fault once we have prepared the page to fault
  *
  * @vmf: structure describing the fault
  *
  * This function handles all that is needed to finish a page fault once the
  * page to fault in is prepared. It handles locking of PTEs, inserts PTE for
  * given page, adds reverse page mapping, handles memcg charges and LRU
  * addition.
  *
  * The function expects the page to be locked and on success it consumes a
  * reference of a page being mapped (for the PTE which maps it).
  *
  * Return: %0 on success, %VM_FAULT_ code in case of error.
  */
 vm_fault_t finish_fault(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         struct page *page;
         struct folio *folio;
         vm_fault_t ret;
         bool is_cow = (vmf->flags & FAULT_FLAG_WRITE) &&
                       !(vma->vm_flags & VM_SHARED);
         int type, nr_pages;
         unsigned long addr = vmf->address;
 
         /* Did we COW the page? */
         if (is_cow)
                 page = vmf->cow_page;
         else
                 page = vmf->page;
 
         /*
          * check even for read faults because we might have lost our CoWed
          * page
          */
         if (!(vma->vm_flags & VM_SHARED)) {
                 ret = check_stable_address_space(vma->vm_mm);
                 if (ret)
                         return ret;
         }
 
         if (pmd_none(*vmf->pmd)) {
                 if (PageTransCompound(page)) {
                         ret = do_set_pmd(vmf, page);
                         if (ret != VM_FAULT_FALLBACK)
                                 return ret;
                 }
 
                 if (vmf->prealloc_pte)
                         pmd_install(vma->vm_mm, vmf->pmd, &vmf->prealloc_pte);
                 else if (unlikely(pte_alloc(vma->vm_mm, vmf->pmd)))
                         return VM_FAULT_OOM;
         }
 
         folio = page_folio(page);
         nr_pages = folio_nr_pages(folio);
 
         /*
          * Using per-page fault to maintain the uffd semantics, and same
          * approach also applies to non-anonymous-shmem faults to avoid
          * inflating the RSS of the process.
          */
         if (!vma_is_anon_shmem(vma) || unlikely(userfaultfd_armed(vma))) {
                 nr_pages = 1;
         } else if (nr_pages > 1) {
                 pgoff_t idx = folio_page_idx(folio, page);
                 /* The page offset of vmf->address within the VMA. */
                 pgoff_t vma_off = vmf->pgoff - vmf->vma->vm_pgoff;
                 /* The index of the entry in the pagetable for fault page. */
                 pgoff_t pte_off = pte_index(vmf->address);
 
                 /*
                  * Fallback to per-page fault in case the folio size in page
                  * cache beyond the VMA limits and PMD pagetable limits.
                  */
                 if (unlikely(vma_off < idx ||
                             vma_off + (nr_pages - idx) > vma_pages(vma) ||
                             pte_off < idx ||
                             pte_off + (nr_pages - idx)  > PTRS_PER_PTE)) {
                         nr_pages = 1;
                 } else {
                         /* Now we can set mappings for the whole large folio. */
                         addr = vmf->address - idx * PAGE_SIZE;
                         page = &folio->page;
                 }
         }
 
         vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
                                        addr, &vmf->ptl);
         if (!vmf->pte)
                 return VM_FAULT_NOPAGE;
 
         /* Re-check under ptl */
         if (nr_pages == 1 && unlikely(vmf_pte_changed(vmf))) {
                 update_mmu_tlb(vma, addr, vmf->pte);
                 ret = VM_FAULT_NOPAGE;
                 goto unlock;
         } else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
                 update_mmu_tlb_range(vma, addr, vmf->pte, nr_pages);
                 ret = VM_FAULT_NOPAGE;
                 goto unlock;
         }
 
         folio_ref_add(folio, nr_pages - 1);
         set_pte_range(vmf, folio, page, nr_pages, addr);
         type = is_cow ? MM_ANONPAGES : mm_counter_file(folio);
         add_mm_counter(vma->vm_mm, type, nr_pages);
         ret = 0;
 
 unlock:
         pte_unmap_unlock(vmf->pte, vmf->ptl);
         return ret;
 }
 
 static unsigned long fault_around_pages __read_mostly =
         65536 >> PAGE_SHIFT;
 
 #ifdef CONFIG_DEBUG_FS
 static int fault_around_bytes_get(void *data, u64 *val)
 {
         *val = fault_around_pages << PAGE_SHIFT;
         return 0;
 }
 
 /*
  * fault_around_bytes must be rounded down to the nearest page order as it's
  * what do_fault_around() expects to see.
  */
 static int fault_around_bytes_set(void *data, u64 val)
 {
         if (val / PAGE_SIZE > PTRS_PER_PTE)
                 return -EINVAL;
 
         /*
          * The minimum value is 1 page, however this results in no fault-around
          * at all. See should_fault_around().
          */
         val = max(val, PAGE_SIZE);
         fault_around_pages = rounddown_pow_of_two(val) >> PAGE_SHIFT;
 
         return 0;
 }
 DEFINE_DEBUGFS_ATTRIBUTE(fault_around_bytes_fops,
                 fault_around_bytes_get, fault_around_bytes_set, "%llu\n");
 
 static int __init fault_around_debugfs(void)
 {
         debugfs_create_file_unsafe("fault_around_bytes", 0644, NULL, NULL,
                                    &fault_around_bytes_fops);
         return 0;
 }
 late_initcall(fault_around_debugfs);
 #endif
 
 /*
  * do_fault_around() tries to map few pages around the fault address. The hope
  * is that the pages will be needed soon and this will lower the number of
  * faults to handle.
  *
  * It uses vm_ops->map_pages() to map the pages, which skips the page if it's
  * not ready to be mapped: not up-to-date, locked, etc.
  *
  * This function doesn't cross VMA or page table boundaries, in order to call
  * map_pages() and acquire a PTE lock only once.
  *
  * fault_around_pages defines how many pages we'll try to map.
  * do_fault_around() expects it to be set to a power of two less than or equal
  * to PTRS_PER_PTE.
  *
  * The virtual address of the area that we map is naturally aligned to
  * fault_around_pages * PAGE_SIZE rounded down to the machine page size
  * (and therefore to page order).  This way it's easier to guarantee
  * that we don't cross page table boundaries.
  */
 static vm_fault_t do_fault_around(struct vm_fault *vmf)
 {
         pgoff_t nr_pages = READ_ONCE(fault_around_pages);
         pgoff_t pte_off = pte_index(vmf->address);
         /* The page offset of vmf->address within the VMA. */
         pgoff_t vma_off = vmf->pgoff - vmf->vma->vm_pgoff;
         pgoff_t from_pte, to_pte;
         vm_fault_t ret;
 
         /* The PTE offset of the start address, clamped to the VMA. */
         from_pte = max(ALIGN_DOWN(pte_off, nr_pages),
                        pte_off - min(pte_off, vma_off));
 
         /* The PTE offset of the end address, clamped to the VMA and PTE. */
         to_pte = min3(from_pte + nr_pages, (pgoff_t)PTRS_PER_PTE,
                       pte_off + vma_pages(vmf->vma) - vma_off) - 1;
 
         if (pmd_none(*vmf->pmd)) {
                 vmf->prealloc_pte = pte_alloc_one(vmf->vma->vm_mm);
                 if (!vmf->prealloc_pte)
                         return VM_FAULT_OOM;
         }
 
         rcu_read_lock();
         ret = vmf->vma->vm_ops->map_pages(vmf,
                         vmf->pgoff + from_pte - pte_off,
                         vmf->pgoff + to_pte - pte_off);
         rcu_read_unlock();
 
         return ret;
 }
 
 /* Return true if we should do read fault-around, false otherwise */
 static inline bool should_fault_around(struct vm_fault *vmf)
 {
         /* No ->map_pages?  No way to fault around... */
         if (!vmf->vma->vm_ops->map_pages)
                 return false;
 
         if (uffd_disable_fault_around(vmf->vma))
                 return false;
 
         /* A single page implies no faulting 'around' at all. */
         return fault_around_pages > 1;
 }
 
 static vm_fault_t do_read_fault(struct vm_fault *vmf)
 {
         vm_fault_t ret = 0;
         struct folio *folio;
 
         /*
          * Let's call ->map_pages() first and use ->fault() as fallback
          * if page by the offset is not ready to be mapped (cold cache or
          * something).
          */
         if (should_fault_around(vmf)) {
                 ret = do_fault_around(vmf);
                 if (ret)
                         return ret;
         }
 
         ret = vmf_can_call_fault(vmf);
         if (ret)
                 return ret;
 
         ret = __do_fault(vmf);
         if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
                 return ret;
 
         ret |= finish_fault(vmf);
         folio = page_folio(vmf->page);
         folio_unlock(folio);
         if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
                 folio_put(folio);
         return ret;
 }
 
 static vm_fault_t do_cow_fault(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         struct folio *folio;
         vm_fault_t ret;
 
         ret = vmf_can_call_fault(vmf);
         if (!ret)
                 ret = vmf_anon_prepare(vmf);
         if (ret)
                 return ret;
 
         folio = folio_prealloc(vma->vm_mm, vma, vmf->address, false);
         if (!folio)
                 return VM_FAULT_OOM;
 
         vmf->cow_page = &folio->page;
 
         ret = __do_fault(vmf);
         if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
                 goto uncharge_out;
         if (ret & VM_FAULT_DONE_COW)
                 return ret;
 
         copy_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma);
         __folio_mark_uptodate(folio);
 
         ret |= finish_fault(vmf);
         unlock_page(vmf->page);
         put_page(vmf->page);
         if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
                 goto uncharge_out;
         return ret;
 uncharge_out:
         folio_put(folio);
         return ret;
 }
 
 static vm_fault_t do_shared_fault(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         vm_fault_t ret, tmp;
         struct folio *folio;
 
         ret = vmf_can_call_fault(vmf);
         if (ret)
                 return ret;
 
         ret = __do_fault(vmf);
         if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
                 return ret;
 
         folio = page_folio(vmf->page);
 
         /*
          * Check if the backing address space wants to know that the page is
          * about to become writable
          */
         if (vma->vm_ops->page_mkwrite) {
                 folio_unlock(folio);
                 tmp = do_page_mkwrite(vmf, folio);
                 if (unlikely(!tmp ||
                                 (tmp & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
                         folio_put(folio);
                         return tmp;
                 }
         }
 
         ret |= finish_fault(vmf);
         if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
                                         VM_FAULT_RETRY))) {
                 folio_unlock(folio);
                 folio_put(folio);
                 return ret;
         }
 
         ret |= fault_dirty_shared_page(vmf);
         return ret;
 }
 
 /*
  * We enter with non-exclusive mmap_lock (to exclude vma changes,
  * but allow concurrent faults).
  * The mmap_lock may have been released depending on flags and our
  * return value.  See filemap_fault() and __folio_lock_or_retry().
  * If mmap_lock is released, vma may become invalid (for example
  * by other thread calling munmap()).
  */
 static vm_fault_t do_fault(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         struct mm_struct *vm_mm = vma->vm_mm;
         vm_fault_t ret;
 
         /*
          * The VMA was not fully populated on mmap() or missing VM_DONTEXPAND
          */
         if (!vma->vm_ops->fault) {
                 vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
                                                vmf->address, &vmf->ptl);
                 if (unlikely(!vmf->pte))
                         ret = VM_FAULT_SIGBUS;
                 else {
                         /*
                          * Make sure this is not a temporary clearing of pte
                          * by holding ptl and checking again. A R/M/W update
                          * of pte involves: take ptl, clearing the pte so that
                          * we don't have concurrent modification by hardware
                          * followed by an update.
                          */
                         if (unlikely(pte_none(ptep_get(vmf->pte))))
                                 ret = VM_FAULT_SIGBUS;
                         else
                                 ret = VM_FAULT_NOPAGE;
 
                         pte_unmap_unlock(vmf->pte, vmf->ptl);
                 }
         } else if (!(vmf->flags & FAULT_FLAG_WRITE))
                 ret = do_read_fault(vmf);
         else if (!(vma->vm_flags & VM_SHARED))
                 ret = do_cow_fault(vmf);
         else
                 ret = do_shared_fault(vmf);
 
         /* preallocated pagetable is unused: free it */
         if (vmf->prealloc_pte) {
                 pte_free(vm_mm, vmf->prealloc_pte);
                 vmf->prealloc_pte = NULL;
         }
         return ret;
 }
 
 int numa_migrate_prep(struct folio *folio, struct vm_fault *vmf,
                       unsigned long addr, int page_nid, int *flags)
 {
         struct vm_area_struct *vma = vmf->vma;
 
         /* Record the current PID acceesing VMA */
         vma_set_access_pid_bit(vma);
 
         count_vm_numa_event(NUMA_HINT_FAULTS);
         if (page_nid == numa_node_id()) {
                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
                 *flags |= TNF_FAULT_LOCAL;
         }
 
         return mpol_misplaced(folio, vmf, addr);
 }
 
 static void numa_rebuild_single_mapping(struct vm_fault *vmf, struct vm_area_struct *vma,
                                         unsigned long fault_addr, pte_t *fault_pte,
                                         bool writable)
 {
         pte_t pte, old_pte;
 
         old_pte = ptep_modify_prot_start(vma, fault_addr, fault_pte);
         pte = pte_modify(old_pte, vma->vm_page_prot);
         pte = pte_mkyoung(pte);
         if (writable)
                 pte = pte_mkwrite(pte, vma);
         ptep_modify_prot_commit(vma, fault_addr, fault_pte, old_pte, pte);
         update_mmu_cache_range(vmf, vma, fault_addr, fault_pte, 1);
 }
 
 static void numa_rebuild_large_mapping(struct vm_fault *vmf, struct vm_area_struct *vma,
                                        struct folio *folio, pte_t fault_pte,
                                        bool ignore_writable, bool pte_write_upgrade)
 {
         int nr = pte_pfn(fault_pte) - folio_pfn(folio);
         unsigned long start, end, addr = vmf->address;
         unsigned long addr_start = addr - (nr << PAGE_SHIFT);
         unsigned long pt_start = ALIGN_DOWN(addr, PMD_SIZE);
         pte_t *start_ptep;
 
         /* Stay within the VMA and within the page table. */
         start = max3(addr_start, pt_start, vma->vm_start);
         end = min3(addr_start + folio_size(folio), pt_start + PMD_SIZE,
                    vma->vm_end);
         start_ptep = vmf->pte - ((addr - start) >> PAGE_SHIFT);
 
         /* Restore all PTEs' mapping of the large folio */
         for (addr = start; addr != end; start_ptep++, addr += PAGE_SIZE) {
                 pte_t ptent = ptep_get(start_ptep);
                 bool writable = false;
 
                 if (!pte_present(ptent) || !pte_protnone(ptent))
                         continue;
 
                 if (pfn_folio(pte_pfn(ptent)) != folio)
                         continue;
 
                 if (!ignore_writable) {
                         ptent = pte_modify(ptent, vma->vm_page_prot);
                         writable = pte_write(ptent);
                         if (!writable && pte_write_upgrade &&
                             can_change_pte_writable(vma, addr, ptent))
                                 writable = true;
                 }
 
                 numa_rebuild_single_mapping(vmf, vma, addr, start_ptep, writable);
         }
 }
 
 static vm_fault_t do_numa_page(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         struct folio *folio = NULL;
         int nid = NUMA_NO_NODE;
         bool writable = false, ignore_writable = false;
         bool pte_write_upgrade = vma_wants_manual_pte_write_upgrade(vma);
         int last_cpupid;
         int target_nid;
         pte_t pte, old_pte;
         int flags = 0, nr_pages;
 
         /*
          * The pte cannot be used safely until we verify, while holding the page
          * table lock, that its contents have not changed during fault handling.
          */
         spin_lock(vmf->ptl);
         /* Read the live PTE from the page tables: */
         old_pte = ptep_get(vmf->pte);
 
         if (unlikely(!pte_same(old_pte, vmf->orig_pte))) {
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
                 return 0;
         }
 
         pte = pte_modify(old_pte, vma->vm_page_prot);
 
         /*
          * Detect now whether the PTE could be writable; this information
          * is only valid while holding the PT lock.
          */
         writable = pte_write(pte);
         if (!writable && pte_write_upgrade &&
             can_change_pte_writable(vma, vmf->address, pte))
                 writable = true;
 
         folio = vm_normal_folio(vma, vmf->address, pte);
         if (!folio || folio_is_zone_device(folio))
                 goto out_map;
 
         /*
          * Avoid grouping on RO pages in general. RO pages shouldn't hurt as
          * much anyway since they can be in shared cache state. This misses
          * the case where a mapping is writable but the process never writes
          * to it but pte_write gets cleared during protection updates and
          * pte_dirty has unpredictable behaviour between PTE scan updates,
          * background writeback, dirty balancing and application behaviour.
          */
         if (!writable)
                 flags |= TNF_NO_GROUP;
 
         /*
          * Flag if the folio is shared between multiple address spaces. This
          * is later used when determining whether to group tasks together
          */
         if (folio_likely_mapped_shared(folio) && (vma->vm_flags & VM_SHARED))
                 flags |= TNF_SHARED;
 
         nid = folio_nid(folio);
         nr_pages = folio_nr_pages(folio);
         /*
          * For memory tiering mode, cpupid of slow memory page is used
          * to record page access time.  So use default value.
          */
         if ((sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) &&
             !node_is_toptier(nid))
                 last_cpupid = (-1 & LAST_CPUPID_MASK);
         else
                 last_cpupid = folio_last_cpupid(folio);
         target_nid = numa_migrate_prep(folio, vmf, vmf->address, nid, &flags);
         if (target_nid == NUMA_NO_NODE)
                 goto out_map;
         if (migrate_misplaced_folio_prepare(folio, vma, target_nid)) {
                 flags |= TNF_MIGRATE_FAIL;
                 goto out_map;
         }
         /* The folio is isolated and isolation code holds a folio reference. */
         pte_unmap_unlock(vmf->pte, vmf->ptl);
         writable = false;
         ignore_writable = true;
 
         /* Migrate to the requested node */
         if (!migrate_misplaced_folio(folio, vma, target_nid)) {
                 nid = target_nid;
                 flags |= TNF_MIGRATED;
                 task_numa_fault(last_cpupid, nid, nr_pages, flags);
                 return 0;
         }
 
         flags |= TNF_MIGRATE_FAIL;
         vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
                                        vmf->address, &vmf->ptl);
         if (unlikely(!vmf->pte))
                 return 0;
         if (unlikely(!pte_same(ptep_get(vmf->pte), vmf->orig_pte))) {
                 pte_unmap_unlock(vmf->pte, vmf->ptl);
                 return 0;
         }
 out_map:
         /*
          * Make it present again, depending on how arch implements
          * non-accessible ptes, some can allow access by kernel mode.
          */
         if (folio && folio_test_large(folio))
                 numa_rebuild_large_mapping(vmf, vma, folio, pte, ignore_writable,
                                            pte_write_upgrade);
         else
                 numa_rebuild_single_mapping(vmf, vma, vmf->address, vmf->pte,
                                             writable);
         pte_unmap_unlock(vmf->pte, vmf->ptl);
 
         if (nid != NUMA_NO_NODE)
                 task_numa_fault(last_cpupid, nid, nr_pages, flags);
         return 0;
 }
 
 static inline vm_fault_t create_huge_pmd(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         if (vma_is_anonymous(vma))
                 return do_huge_pmd_anonymous_page(vmf);
         if (vma->vm_ops->huge_fault)
                 return vma->vm_ops->huge_fault(vmf, PMD_ORDER);
         return VM_FAULT_FALLBACK;
 }
 
 /* `inline' is required to avoid gcc 4.1.2 build error */
 static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
         vm_fault_t ret;
 
         if (vma_is_anonymous(vma)) {
                 if (likely(!unshare) &&
                     userfaultfd_huge_pmd_wp(vma, vmf->orig_pmd)) {
                         if (userfaultfd_wp_async(vmf->vma))
                                 goto split;
                         return handle_userfault(vmf, VM_UFFD_WP);
                 }
                 return do_huge_pmd_wp_page(vmf);
         }
 
         if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) {
                 if (vma->vm_ops->huge_fault) {
                         ret = vma->vm_ops->huge_fault(vmf, PMD_ORDER);
                         if (!(ret & VM_FAULT_FALLBACK))
                                 return ret;
                 }
         }
 
 split:
         /* COW or write-notify handled on pte level: split pmd. */
         __split_huge_pmd(vma, vmf->pmd, vmf->address, false, NULL);
 
         return VM_FAULT_FALLBACK;
 }
 
 static vm_fault_t create_huge_pud(struct vm_fault *vmf)
 {
 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) &&                     \
         defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
         struct vm_area_struct *vma = vmf->vma;
         /* No support for anonymous transparent PUD pages yet */
         if (vma_is_anonymous(vma))
                 return VM_FAULT_FALLBACK;
         if (vma->vm_ops->huge_fault)
                 return vma->vm_ops->huge_fault(vmf, PUD_ORDER);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
         return VM_FAULT_FALLBACK;
 }
 
 static vm_fault_t wp_huge_pud(struct vm_fault *vmf, pud_t orig_pud)
 {
 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) &&                     \
         defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
         struct vm_area_struct *vma = vmf->vma;
         vm_fault_t ret;
 
         /* No support for anonymous transparent PUD pages yet */
         if (vma_is_anonymous(vma))
                 goto split;
         if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) {
                 if (vma->vm_ops->huge_fault) {
                         ret = vma->vm_ops->huge_fault(vmf, PUD_ORDER);
                         if (!(ret & VM_FAULT_FALLBACK))
                                 return ret;
                 }
         }
 split:
         /* COW or write-notify not handled on PUD level: split pud.*/
         __split_huge_pud(vma, vmf->pud, vmf->address);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE && CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
         return VM_FAULT_FALLBACK;
 }
 
 /*
  * These routines also need to handle stuff like marking pages dirty
  * and/or accessed for architectures that don't do it in hardware (most
  * RISC architectures).  The early dirtying is also good on the i386.
  *
  * There is also a hook called "update_mmu_cache()" that architectures
  * with external mmu caches can use to update those (ie the Sparc or
  * PowerPC hashed page tables that act as extended TLBs).
  *
  * We enter with non-exclusive mmap_lock (to exclude vma changes, but allow
  * concurrent faults).
  *
  * The mmap_lock may have been released depending on flags and our return value.
  * See filemap_fault() and __folio_lock_or_retry().
  */
 static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 {
         pte_t entry;
 
         if (unlikely(pmd_none(*vmf->pmd))) {
                 /*
                  * Leave __pte_alloc() until later: because vm_ops->fault may
                  * want to allocate huge page, and if we expose page table
                  * for an instant, it will be difficult to retract from
                  * concurrent faults and from rmap lookups.
                  */
                 vmf->pte = NULL;
                 vmf->flags &= ~FAULT_FLAG_ORIG_PTE_VALID;
         } else {
                 /*
                  * A regular pmd is established and it can't morph into a huge
                  * pmd by anon khugepaged, since that takes mmap_lock in write
                  * mode; but shmem or file collapse to THP could still morph
                  * it into a huge pmd: just retry later if so.
                  */
                 vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm, vmf->pmd,
                                                  vmf->address, &vmf->ptl);
                 if (unlikely(!vmf->pte))
                         return 0;
                 vmf->orig_pte = ptep_get_lockless(vmf->pte);
                 vmf->flags |= FAULT_FLAG_ORIG_PTE_VALID;
 
                 if (pte_none(vmf->orig_pte)) {
                         pte_unmap(vmf->pte);
                         vmf->pte = NULL;
                 }
         }
 
         if (!vmf->pte)
                 return do_pte_missing(vmf);
 
         if (!pte_present(vmf->orig_pte))
                 return do_swap_page(vmf);
 
         if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma))
                 return do_numa_page(vmf);
 
         spin_lock(vmf->ptl);
         entry = vmf->orig_pte;
         if (unlikely(!pte_same(ptep_get(vmf->pte), entry))) {
                 update_mmu_tlb(vmf->vma, vmf->address, vmf->pte);
                 goto unlock;
         }
         if (vmf->flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) {
                 if (!pte_write(entry))
                         return do_wp_page(vmf);
                 else if (likely(vmf->flags & FAULT_FLAG_WRITE))
                         entry = pte_mkdirty(entry);
         }
         entry = pte_mkyoung(entry);
         if (ptep_set_access_flags(vmf->vma, vmf->address, vmf->pte, entry,
                                 vmf->flags & FAULT_FLAG_WRITE)) {
                 update_mmu_cache_range(vmf, vmf->vma, vmf->address,
                                 vmf->pte, 1);
         } else {
                 /* Skip spurious TLB flush for retried page fault */
                 if (vmf->flags & FAULT_FLAG_TRIED)
                         goto unlock;
                 /*
                  * This is needed only for protection faults but the arch code
                  * is not yet telling us if this is a protection fault or not.
                  * This still avoids useless tlb flushes for .text page faults
                  * with threads.
                  */
                 if (vmf->flags & FAULT_FLAG_WRITE)
                         flush_tlb_fix_spurious_fault(vmf->vma, vmf->address,
                                                      vmf->pte);
         }
 unlock:
         pte_unmap_unlock(vmf->pte, vmf->ptl);
         return 0;
 }
 
 /*
  * On entry, we hold either the VMA lock or the mmap_lock
  * (FAULT_FLAG_VMA_LOCK tells you which).  If VM_FAULT_RETRY is set in
  * the result, the mmap_lock is not held on exit.  See filemap_fault()
  * and __folio_lock_or_retry().
  */
 static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
                 unsigned long address, unsigned int flags)
 {
         struct vm_fault vmf = {
                 .vma = vma,
                 .address = address & PAGE_MASK,
                 .real_address = address,
                 .flags = flags,
                 .pgoff = linear_page_index(vma, address),
                 .gfp_mask = __get_fault_gfp_mask(vma),
         };
         struct mm_struct *mm = vma->vm_mm;
         unsigned long vm_flags = vma->vm_flags;
         pgd_t *pgd;
         p4d_t *p4d;
         vm_fault_t ret;
 
         pgd = pgd_offset(mm, address);
         p4d = p4d_alloc(mm, pgd, address);
         if (!p4d)
                 return VM_FAULT_OOM;
 
         vmf.pud = pud_alloc(mm, p4d, address);
         if (!vmf.pud)
                 return VM_FAULT_OOM;
 retry_pud:
         if (pud_none(*vmf.pud) &&
             thp_vma_allowable_order(vma, vm_flags,
                                 TVA_IN_PF | TVA_ENFORCE_SYSFS, PUD_ORDER)) {
                 ret = create_huge_pud(&vmf);
                 if (!(ret & VM_FAULT_FALLBACK))
                         return ret;
         } else {
                 pud_t orig_pud = *vmf.pud;
 
                 barrier();
                 if (pud_trans_huge(orig_pud) || pud_devmap(orig_pud)) {
 
                         /*
                          * TODO once we support anonymous PUDs: NUMA case and
                          * FAULT_FLAG_UNSHARE handling.
                          */
                         if ((flags & FAULT_FLAG_WRITE) && !pud_write(orig_pud)) {
                                 ret = wp_huge_pud(&vmf, orig_pud);
                                 if (!(ret & VM_FAULT_FALLBACK))
                                         return ret;
                         } else {
                                 huge_pud_set_accessed(&vmf, orig_pud);
                                 return 0;
                         }
                 }
         }
 
         vmf.pmd = pmd_alloc(mm, vmf.pud, address);
         if (!vmf.pmd)
                 return VM_FAULT_OOM;
 
         /* Huge pud page fault raced with pmd_alloc? */
         if (pud_trans_unstable(vmf.pud))
                 goto retry_pud;
 
         if (pmd_none(*vmf.pmd) &&
             thp_vma_allowable_order(vma, vm_flags,
                                 TVA_IN_PF | TVA_ENFORCE_SYSFS, PMD_ORDER)) {
                 ret = create_huge_pmd(&vmf);
                 if (!(ret & VM_FAULT_FALLBACK))
                         return ret;
         } else {
                 vmf.orig_pmd = pmdp_get_lockless(vmf.pmd);
 
                 if (unlikely(is_swap_pmd(vmf.orig_pmd))) {
                         VM_BUG_ON(thp_migration_supported() &&
                                           !is_pmd_migration_entry(vmf.orig_pmd));
                         if (is_pmd_migration_entry(vmf.orig_pmd))
                                 pmd_migration_entry_wait(mm, vmf.pmd);
                         return 0;
                 }
                 if (pmd_trans_huge(vmf.orig_pmd) || pmd_devmap(vmf.orig_pmd)) {
                         if (pmd_protnone(vmf.orig_pmd) && vma_is_accessible(vma))
                                 return do_huge_pmd_numa_page(&vmf);
 
                         if ((flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) &&
                             !pmd_write(vmf.orig_pmd)) {
                                 ret = wp_huge_pmd(&vmf);
                                 if (!(ret & VM_FAULT_FALLBACK))
                                         return ret;
                         } else {
                                 huge_pmd_set_accessed(&vmf);
                                 return 0;
                         }
                 }
         }
 
         return handle_pte_fault(&vmf);
 }
 
 /**
  * mm_account_fault - Do page fault accounting
  * @mm: mm from which memcg should be extracted. It can be NULL.
  * @regs: the pt_regs struct pointer.  When set to NULL, will skip accounting
  *        of perf event counters, but we'll still do the per-task accounting to
  *        the task who triggered this page fault.
  * @address: the faulted address.
  * @flags: the fault flags.
  * @ret: the fault retcode.
  *
  * This will take care of most of the page fault accounting.  Meanwhile, it
  * will also include the PERF_COUNT_SW_PAGE_FAULTS_[MAJ|MIN] perf counter
  * updates.  However, note that the handling of PERF_COUNT_SW_PAGE_FAULTS should
  * still be in per-arch page fault handlers at the entry of page fault.
  */
 static inline void mm_account_fault(struct mm_struct *mm, struct pt_regs *regs,
                                     unsigned long address, unsigned int flags,
                                     vm_fault_t ret)
 {
         bool major;
 
         /* Incomplete faults will be accounted upon completion. */
         if (ret & VM_FAULT_RETRY)
                 return;
 
         /*
          * To preserve the behavior of older kernels, PGFAULT counters record
          * both successful and failed faults, as opposed to perf counters,
          * which ignore failed cases.
          */
         count_vm_event(PGFAULT);
         count_memcg_event_mm(mm, PGFAULT);
 
         /*
          * Do not account for unsuccessful faults (e.g. when the address wasn't
          * valid).  That includes arch_vma_access_permitted() failing before
          * reaching here. So this is not a "this many hardware page faults"
          * counter.  We should use the hw profiling for that.
          */
         if (ret & VM_FAULT_ERROR)
                 return;
 
         /*
          * We define the fault as a major fault when the final successful fault
          * is VM_FAULT_MAJOR, or if it retried (which implies that we couldn't
          * handle it immediately previously).
          */
         major = (ret & VM_FAULT_MAJOR) || (flags & FAULT_FLAG_TRIED);
 
         if (major)
                 current->maj_flt++;
         else
                 current->min_flt++;
 
         /*
          * If the fault is done for GUP, regs will be NULL.  We only do the
          * accounting for the per thread fault counters who triggered the
          * fault, and we skip the perf event updates.
          */
         if (!regs)
                 return;
 
         if (major)
                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
         else
                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
 }
 
 #ifdef CONFIG_LRU_GEN
 static void lru_gen_enter_fault(struct vm_area_struct *vma)
 {
         /* the LRU algorithm only applies to accesses with recency */
         current->in_lru_fault = vma_has_recency(vma);
 }
 
 static void lru_gen_exit_fault(void)
 {
         current->in_lru_fault = false;
 }
 #else
 static void lru_gen_enter_fault(struct vm_area_struct *vma)
 {
 }
 
 static void lru_gen_exit_fault(void)
 {
 }
 #endif /* CONFIG_LRU_GEN */
 
 static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma,
                                        unsigned int *flags)
 {
         if (unlikely(*flags & FAULT_FLAG_UNSHARE)) {
                 if (WARN_ON_ONCE(*flags & FAULT_FLAG_WRITE))
                         return VM_FAULT_SIGSEGV;
                 /*
                  * FAULT_FLAG_UNSHARE only applies to COW mappings. Let's
                  * just treat it like an ordinary read-fault otherwise.
                  */
                 if (!is_cow_mapping(vma->vm_flags))
                         *flags &= ~FAULT_FLAG_UNSHARE;
         } else if (*flags & FAULT_FLAG_WRITE) {
                 /* Write faults on read-only mappings are impossible ... */
                 if (WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE)))
                         return VM_FAULT_SIGSEGV;
                 /* ... and FOLL_FORCE only applies to COW mappings. */
                 if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE) &&
                                  !is_cow_mapping(vma->vm_flags)))
                         return VM_FAULT_SIGSEGV;
         }
 #ifdef CONFIG_PER_VMA_LOCK
         /*
          * Per-VMA locks can't be used with FAULT_FLAG_RETRY_NOWAIT because of
          * the assumption that lock is dropped on VM_FAULT_RETRY.
          */
         if (WARN_ON_ONCE((*flags &
                         (FAULT_FLAG_VMA_LOCK | FAULT_FLAG_RETRY_NOWAIT)) ==
                         (FAULT_FLAG_VMA_LOCK | FAULT_FLAG_RETRY_NOWAIT)))
                 return VM_FAULT_SIGSEGV;
 #endif
 
         return 0;
 }
 
 /*
  * By the time we get here, we already hold the mm semaphore
  *
  * The mmap_lock may have been released depending on flags and our
  * return value.  See filemap_fault() and __folio_lock_or_retry().
  */
 vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
                            unsigned int flags, struct pt_regs *regs)
 {
         /* If the fault handler drops the mmap_lock, vma may be freed */
         struct mm_struct *mm = vma->vm_mm;
         vm_fault_t ret;
         bool is_droppable;
 
         __set_current_state(TASK_RUNNING);
 
         ret = sanitize_fault_flags(vma, &flags);
         if (ret)
                 goto out;
 
         if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
                                             flags & FAULT_FLAG_INSTRUCTION,
                                             flags & FAULT_FLAG_REMOTE)) {
                 ret = VM_FAULT_SIGSEGV;
                 goto out;
         }
 
         is_droppable = !!(vma->vm_flags & VM_DROPPABLE);
 
         /*
          * Enable the memcg OOM handling for faults triggered in user
          * space.  Kernel faults are handled more gracefully.
          */
         if (flags & FAULT_FLAG_USER)
                 mem_cgroup_enter_user_fault();
 
         lru_gen_enter_fault(vma);
 
         if (unlikely(is_vm_hugetlb_page(vma)))
                 ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
         else
                 ret = __handle_mm_fault(vma, address, flags);
 
         /*
          * Warning: It is no longer safe to dereference vma-> after this point,
          * because mmap_lock might have been dropped by __handle_mm_fault(), so
          * vma might be destroyed from underneath us.
          */
 
         lru_gen_exit_fault();
 
         /* If the mapping is droppable, then errors due to OOM aren't fatal. */
         if (is_droppable)
                 ret &= ~VM_FAULT_OOM;
 
         if (flags & FAULT_FLAG_USER) {
                 mem_cgroup_exit_user_fault();
                 /*
                  * The task may have entered a memcg OOM situation but
                  * if the allocation error was handled gracefully (no
                  * VM_FAULT_OOM), there is no need to kill anything.
                  * Just clean up the OOM state peacefully.
                  */
                 if (task_in_memcg_oom(current) && !(ret & VM_FAULT_OOM))
                         mem_cgroup_oom_synchronize(false);
         }
 out:
         mm_account_fault(mm, regs, address, flags, ret);
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(handle_mm_fault);
 
 #ifdef CONFIG_LOCK_MM_AND_FIND_VMA
 #include <linux/extable.h>
 
 static inline bool get_mmap_lock_carefully(struct mm_struct *mm, struct pt_regs *regs)
 {
         if (likely(mmap_read_trylock(mm)))
                 return true;
 
         if (regs && !user_mode(regs)) {
                 unsigned long ip = exception_ip(regs);
                 if (!search_exception_tables(ip))
                         return false;
         }
 
         return !mmap_read_lock_killable(mm);
 }
 
 static inline bool mmap_upgrade_trylock(struct mm_struct *mm)
 {
         /*
          * We don't have this operation yet.
          *
          * It should be easy enough to do: it's basically a
          *    atomic_long_try_cmpxchg_acquire()
          * from RWSEM_READER_BIAS -> RWSEM_WRITER_LOCKED, but
          * it also needs the proper lockdep magic etc.
          */
         return false;
 }
 
 static inline bool upgrade_mmap_lock_carefully(struct mm_struct *mm, struct pt_regs *regs)
 {
         mmap_read_unlock(mm);
         if (regs && !user_mode(regs)) {
                 unsigned long ip = exception_ip(regs);
                 if (!search_exception_tables(ip))
                         return false;
         }
         return !mmap_write_lock_killable(mm);
 }
 
 /*
  * Helper for page fault handling.
  *
  * This is kind of equivalend to "mmap_read_lock()" followed
  * by "find_extend_vma()", except it's a lot more careful about
  * the locking (and will drop the lock on failure).
  *
  * For example, if we have a kernel bug that causes a page
  * fault, we don't want to just use mmap_read_lock() to get
  * the mm lock, because that would deadlock if the bug were
  * to happen while we're holding the mm lock for writing.
  *
  * So this checks the exception tables on kernel faults in
  * order to only do this all for instructions that are actually
  * expected to fault.
  *
  * We can also actually take the mm lock for writing if we
  * need to extend the vma, which helps the VM layer a lot.
  */
 struct vm_area_struct *lock_mm_and_find_vma(struct mm_struct *mm,
                         unsigned long addr, struct pt_regs *regs)
 {
         struct vm_area_struct *vma;
 
         if (!get_mmap_lock_carefully(mm, regs))
                 return NULL;
 
         vma = find_vma(mm, addr);
         if (likely(vma && (vma->vm_start <= addr)))
                 return vma;
 
         /*
          * Well, dang. We might still be successful, but only
          * if we can extend a vma to do so.
          */
         if (!vma || !(vma->vm_flags & VM_GROWSDOWN)) {
                 mmap_read_unlock(mm);
                 return NULL;
         }
 
         /*
          * We can try to upgrade the mmap lock atomically,
          * in which case we can continue to use the vma
          * we already looked up.
          *
          * Otherwise we'll have to drop the mmap lock and
          * re-take it, and also look up the vma again,
          * re-checking it.
          */
         if (!mmap_upgrade_trylock(mm)) {
                 if (!upgrade_mmap_lock_carefully(mm, regs))
                         return NULL;
 
                 vma = find_vma(mm, addr);
                 if (!vma)
                         goto fail;
                 if (vma->vm_start <= addr)
                         goto success;
                 if (!(vma->vm_flags & VM_GROWSDOWN))
                         goto fail;
         }
 
         if (expand_stack_locked(vma, addr))
                 goto fail;
 
 success:
         mmap_write_downgrade(mm);
         return vma;
 
 fail:
         mmap_write_unlock(mm);
         return NULL;
 }
 #endif
 
 #ifdef CONFIG_PER_VMA_LOCK
 /*
  * Lookup and lock a VMA under RCU protection. Returned VMA is guaranteed to be
  * stable and not isolated. If the VMA is not found or is being modified the
  * function returns NULL.
  */
 struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
                                           unsigned long address)
 {
         MA_STATE(mas, &mm->mm_mt, address, address);
         struct vm_area_struct *vma;
 
         rcu_read_lock();
 retry:
         vma = mas_walk(&mas);
         if (!vma)
                 goto inval;
 
         if (!vma_start_read(vma))
                 goto inval;
 
         /* Check since vm_start/vm_end might change before we lock the VMA */
         if (unlikely(address < vma->vm_start || address >= vma->vm_end))
                 goto inval_end_read;
 
         /* Check if the VMA got isolated after we found it */
         if (vma->detached) {
                 vma_end_read(vma);
                 count_vm_vma_lock_event(VMA_LOCK_MISS);
                 /* The area was replaced with another one */
                 goto retry;
         }
 
         rcu_read_unlock();
         return vma;
 
 inval_end_read:
         vma_end_read(vma);
 inval:
         rcu_read_unlock();
         count_vm_vma_lock_event(VMA_LOCK_ABORT);
         return NULL;
 }
 #endif /* CONFIG_PER_VMA_LOCK */
 
 #ifndef __PAGETABLE_P4D_FOLDED
 /*
  * Allocate p4d page table.
  * We've already handled the fast-path in-line.
  */
 int __p4d_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
 {
         p4d_t *new = p4d_alloc_one(mm, address);
         if (!new)
                 return -ENOMEM;
 
         spin_lock(&mm->page_table_lock);
         if (pgd_present(*pgd)) {        /* Another has populated it */
                 p4d_free(mm, new);
         } else {
                 smp_wmb(); /* See comment in pmd_install() */
                 pgd_populate(mm, pgd, new);
         }
         spin_unlock(&mm->page_table_lock);
         return 0;
 }
 #endif /* __PAGETABLE_P4D_FOLDED */
 
 #ifndef __PAGETABLE_PUD_FOLDED
 /*
  * Allocate page upper directory.
  * We've already handled the fast-path in-line.
  */
 int __pud_alloc(struct mm_struct *mm, p4d_t *p4d, unsigned long address)
 {
         pud_t *new = pud_alloc_one(mm, address);
         if (!new)
                 return -ENOMEM;
 
         spin_lock(&mm->page_table_lock);
         if (!p4d_present(*p4d)) {
                 mm_inc_nr_puds(mm);
                 smp_wmb(); /* See comment in pmd_install() */
                 p4d_populate(mm, p4d, new);
         } else  /* Another has populated it */
                 pud_free(mm, new);
         spin_unlock(&mm->page_table_lock);
         return 0;
 }
 #endif /* __PAGETABLE_PUD_FOLDED */
 
 #ifndef __PAGETABLE_PMD_FOLDED
 /*
  * Allocate page middle directory.
  * We've already handled the fast-path in-line.
  */
 int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
 {
         spinlock_t *ptl;
         pmd_t *new = pmd_alloc_one(mm, address);
         if (!new)
                 return -ENOMEM;
 
         ptl = pud_lock(mm, pud);
         if (!pud_present(*pud)) {
                 mm_inc_nr_pmds(mm);
                 smp_wmb(); /* See comment in pmd_install() */
                 pud_populate(mm, pud, new);
         } else {        /* Another has populated it */
                 pmd_free(mm, new);
         }
         spin_unlock(ptl);
         return 0;
 }
 #endif /* __PAGETABLE_PMD_FOLDED */
 
 /**
  * follow_pte - look up PTE at a user virtual address
  * @vma: the memory mapping
  * @address: user virtual address
  * @ptepp: location to store found PTE
  * @ptlp: location to store the lock for the PTE
  *
  * On a successful return, the pointer to the PTE is stored in @ptepp;
  * the corresponding lock is taken and its location is stored in @ptlp.
  *
  * The contents of the PTE are only stable until @ptlp is released using
  * pte_unmap_unlock(). This function will fail if the PTE is non-present.
  * Present PTEs may include PTEs that map refcounted pages, such as
  * anonymous folios in COW mappings.
  *
  * Callers must be careful when relying on PTE content after
  * pte_unmap_unlock(). Especially if the PTE maps a refcounted page,
  * callers must protect against invalidation with MMU notifiers; otherwise
  * access to the PFN at a later point in time can trigger use-after-free.
  *
  * Only IO mappings and raw PFN mappings are allowed.  The mmap semaphore
  * should be taken for read.
  *
  * This function must not be used to modify PTE content.
  *
  * Return: zero on success, -ve otherwise.
  */
 int follow_pte(struct vm_area_struct *vma, unsigned long address,
                pte_t **ptepp, spinlock_t **ptlp)
 {
         struct mm_struct *mm = vma->vm_mm;
         pgd_t *pgd;
         p4d_t *p4d;
         pud_t *pud;
         pmd_t *pmd;
         pte_t *ptep;
 
         mmap_assert_locked(mm);
         if (unlikely(address < vma->vm_start || address >= vma->vm_end))
                 goto out;
 
         if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
                 goto out;
 
         pgd = pgd_offset(mm, address);
         if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
                 goto out;
 
         p4d = p4d_offset(pgd, address);
         if (p4d_none(*p4d) || unlikely(p4d_bad(*p4d)))
                 goto out;
 
         pud = pud_offset(p4d, address);
         if (pud_none(*pud) || unlikely(pud_bad(*pud)))
                 goto out;
 
         pmd = pmd_offset(pud, address);
         VM_BUG_ON(pmd_trans_huge(*pmd));
 
         ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
         if (!ptep)
                 goto out;
         if (!pte_present(ptep_get(ptep)))
                 goto unlock;
         *ptepp = ptep;
         return 0;
 unlock:
         pte_unmap_unlock(ptep, *ptlp);
 out:
         return -EINVAL;
 }
 EXPORT_SYMBOL_GPL(follow_pte);
 
 #ifdef CONFIG_HAVE_IOREMAP_PROT
 /**
  * generic_access_phys - generic implementation for iomem mmap access
  * @vma: the vma to access
  * @addr: userspace address, not relative offset within @vma
  * @buf: buffer to read/write
  * @len: length of transfer
  * @write: set to FOLL_WRITE when writing, otherwise reading
  *
  * This is a generic implementation for &vm_operations_struct.access for an
  * iomem mapping. This callback is used by access_process_vm() when the @vma is
  * not page based.
  */
 int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
                         void *buf, int len, int write)
 {
         resource_size_t phys_addr;
         unsigned long prot = 0;
         void __iomem *maddr;
         pte_t *ptep, pte;
         spinlock_t *ptl;
         int offset = offset_in_page(addr);
         int ret = -EINVAL;
 
 retry:
         if (follow_pte(vma, addr, &ptep, &ptl))
                 return -EINVAL;
         pte = ptep_get(ptep);
         pte_unmap_unlock(ptep, ptl);
 
         prot = pgprot_val(pte_pgprot(pte));
         phys_addr = (resource_size_t)pte_pfn(pte) << PAGE_SHIFT;
 
         if ((write & FOLL_WRITE) && !pte_write(pte))
                 return -EINVAL;
 
         maddr = ioremap_prot(phys_addr, PAGE_ALIGN(len + offset), prot);
         if (!maddr)
                 return -ENOMEM;
 
         if (follow_pte(vma, addr, &ptep, &ptl))
                 goto out_unmap;
 
         if (!pte_same(pte, ptep_get(ptep))) {
                 pte_unmap_unlock(ptep, ptl);
                 iounmap(maddr);
 
                 goto retry;
         }
 
         if (write)
                 memcpy_toio(maddr + offset, buf, len);
         else
                 memcpy_fromio(buf, maddr + offset, len);
         ret = len;
         pte_unmap_unlock(ptep, ptl);
 out_unmap:
         iounmap(maddr);
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(generic_access_phys);
 #endif
 
 /*
  * Access another process' address space as given in mm.
  */
 static int __access_remote_vm(struct mm_struct *mm, unsigned long addr,
                               void *buf, int len, unsigned int gup_flags)
 {
         void *old_buf = buf;
         int write = gup_flags & FOLL_WRITE;
 
         if (mmap_read_lock_killable(mm))
                 return 0;
 
         /* Untag the address before looking up the VMA */
         addr = untagged_addr_remote(mm, addr);
 
         /* Avoid triggering the temporary warning in __get_user_pages */
         if (!vma_lookup(mm, addr) && !expand_stack(mm, addr))
                 return 0;
 
         /* ignore errors, just check how much was successfully transferred */
         while (len) {
                 int bytes, offset;
                 void *maddr;
                 struct vm_area_struct *vma = NULL;
                 struct page *page = get_user_page_vma_remote(mm, addr,
                                                              gup_flags, &vma);
 
                 if (IS_ERR(page)) {
                         /* We might need to expand the stack to access it */
                         vma = vma_lookup(mm, addr);
                         if (!vma) {
                                 vma = expand_stack(mm, addr);
 
                                 /* mmap_lock was dropped on failure */
                                 if (!vma)
                                         return buf - old_buf;
 
                                 /* Try again if stack expansion worked */
                                 continue;
                         }
 
                         /*
                          * Check if this is a VM_IO | VM_PFNMAP VMA, which
                          * we can access using slightly different code.
                          */
                         bytes = 0;
 #ifdef CONFIG_HAVE_IOREMAP_PROT
                         if (vma->vm_ops && vma->vm_ops->access)
                                 bytes = vma->vm_ops->access(vma, addr, buf,
                                                             len, write);
 #endif
                         if (bytes <= 0)
                                 break;
                 } else {
                         bytes = len;
                         offset = addr & (PAGE_SIZE-1);
                         if (bytes > PAGE_SIZE-offset)
                                 bytes = PAGE_SIZE-offset;
 
                         maddr = kmap_local_page(page);
                         if (write) {
                                 copy_to_user_page(vma, page, addr,
                                                   maddr + offset, buf, bytes);
                                 set_page_dirty_lock(page);
                         } else {
                                 copy_from_user_page(vma, page, addr,
                                                     buf, maddr + offset, bytes);
                         }
                         unmap_and_put_page(page, maddr);
                 }
                 len -= bytes;
                 buf += bytes;
                 addr += bytes;
         }
         mmap_read_unlock(mm);
 
         return buf - old_buf;
 }
 
 /**
  * access_remote_vm - access another process' address space
  * @mm:         the mm_struct of the target address space
  * @addr:       start address to access
  * @buf:        source or destination buffer
  * @len:        number of bytes to transfer
  * @gup_flags:  flags modifying lookup behaviour
  *
  * The caller must hold a reference on @mm.
  *
  * Return: number of bytes copied from source to destination.
  */
 int access_remote_vm(struct mm_struct *mm, unsigned long addr,
                 void *buf, int len, unsigned int gup_flags)
 {
         return __access_remote_vm(mm, addr, buf, len, gup_flags);
 }
 
 /*
  * Access another process' address space.
  * Source/target buffer must be kernel space,
  * Do not walk the page table directly, use get_user_pages
  */
 int access_process_vm(struct task_struct *tsk, unsigned long addr,
                 void *buf, int len, unsigned int gup_flags)
 {
         struct mm_struct *mm;
         int ret;
 
         mm = get_task_mm(tsk);
         if (!mm)
                 return 0;
 
         ret = __access_remote_vm(mm, addr, buf, len, gup_flags);
 
         mmput(mm);
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(access_process_vm);
 
 /*
  * Print the name of a VMA.
  */
 void print_vma_addr(char *prefix, unsigned long ip)
 {
         struct mm_struct *mm = current->mm;
         struct vm_area_struct *vma;
 
         /*
          * we might be running from an atomic context so we cannot sleep
          */
         if (!mmap_read_trylock(mm))
                 return;
 
         vma = vma_lookup(mm, ip);
         if (vma && vma->vm_file) {
                 struct file *f = vma->vm_file;
                 ip -= vma->vm_start;
                 ip += vma->vm_pgoff << PAGE_SHIFT;
                 printk("%s%pD[%lx,%lx+%lx]", prefix, f, ip,
                                 vma->vm_start,
                                 vma->vm_end - vma->vm_start);
         }
         mmap_read_unlock(mm);
 }
 
 #if defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP)
 void __might_fault(const char *file, int line)
 {
         if (pagefault_disabled())
                 return;
         __might_sleep(file, line);
 #if defined(CONFIG_DEBUG_ATOMIC_SLEEP)
         if (current->mm)
                 might_lock_read(&current->mm->mmap_lock);
 #endif
 }
 EXPORT_SYMBOL(__might_fault);
 #endif
 
 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
 /*
  * Process all subpages of the specified huge page with the specified
  * operation.  The target subpage will be processed last to keep its
  * cache lines hot.
  */
 static inline int process_huge_page(
         unsigned long addr_hint, unsigned int nr_pages,
         int (*process_subpage)(unsigned long addr, int idx, void *arg),
         void *arg)
 {
         int i, n, base, l, ret;
         unsigned long addr = addr_hint &
                 ~(((unsigned long)nr_pages << PAGE_SHIFT) - 1);
 
         /* Process target subpage last to keep its cache lines hot */
         might_sleep();
         n = (addr_hint - addr) / PAGE_SIZE;
         if (2 * n <= nr_pages) {
                 /* If target subpage in first half of huge page */
                 base = 0;
                 l = n;
                 /* Process subpages at the end of huge page */
                 for (i = nr_pages - 1; i >= 2 * n; i--) {
                         cond_resched();
                         ret = process_subpage(addr + i * PAGE_SIZE, i, arg);
                         if (ret)
                                 return ret;
                 }
         } else {
                 /* If target subpage in second half of huge page */
                 base = nr_pages - 2 * (nr_pages - n);
                 l = nr_pages - n;
                 /* Process subpages at the begin of huge page */
                 for (i = 0; i < base; i++) {
                         cond_resched();
                         ret = process_subpage(addr + i * PAGE_SIZE, i, arg);
                         if (ret)
                                 return ret;
                 }
         }
         /*
          * Process remaining subpages in left-right-left-right pattern
          * towards the target subpage
          */
         for (i = 0; i < l; i++) {
                 int left_idx = base + i;
                 int right_idx = base + 2 * l - 1 - i;
 
                 cond_resched();
                 ret = process_subpage(addr + left_idx * PAGE_SIZE, left_idx, arg);
                 if (ret)
                         return ret;
                 cond_resched();
                 ret = process_subpage(addr + right_idx * PAGE_SIZE, right_idx, arg);
                 if (ret)
                         return ret;
         }
         return 0;
 }
 
 static void clear_gigantic_page(struct folio *folio, unsigned long addr,
                                 unsigned int nr_pages)
 {
         int i;
 
         might_sleep();
         for (i = 0; i < nr_pages; i++) {
                 cond_resched();
                 clear_user_highpage(folio_page(folio, i), addr + i * PAGE_SIZE);
         }
 }
 
 static int clear_subpage(unsigned long addr, int idx, void *arg)
 {
         struct folio *folio = arg;
 
         clear_user_highpage(folio_page(folio, idx), addr);
         return 0;
 }
 
 /**
  * folio_zero_user - Zero a folio which will be mapped to userspace.
  * @folio: The folio to zero.
  * @addr_hint: The address will be accessed or the base address if uncelar.
  */
 void folio_zero_user(struct folio *folio, unsigned long addr_hint)
 {
         unsigned int nr_pages = folio_nr_pages(folio);
 
         if (unlikely(nr_pages > MAX_ORDER_NR_PAGES))
                 clear_gigantic_page(folio, addr_hint, nr_pages);
         else
                 process_huge_page(addr_hint, nr_pages, clear_subpage, folio);
 }
 
 static int copy_user_gigantic_page(struct folio *dst, struct folio *src,
                                    unsigned long addr,
                                    struct vm_area_struct *vma,
                                    unsigned int nr_pages)
 {
         int i;
         struct page *dst_page;
         struct page *src_page;
 
         for (i = 0; i < nr_pages; i++) {
                 dst_page = folio_page(dst, i);
                 src_page = folio_page(src, i);
 
                 cond_resched();
                 if (copy_mc_user_highpage(dst_page, src_page,
                                           addr + i*PAGE_SIZE, vma))
                         return -EHWPOISON;
         }
         return 0;
 }
 
 struct copy_subpage_arg {
         struct folio *dst;
         struct folio *src;
         struct vm_area_struct *vma;
 };
 
 static int copy_subpage(unsigned long addr, int idx, void *arg)
 {
         struct copy_subpage_arg *copy_arg = arg;
         struct page *dst = folio_page(copy_arg->dst, idx);
         struct page *src = folio_page(copy_arg->src, idx);
 
         if (copy_mc_user_highpage(dst, src, addr, copy_arg->vma))
                 return -EHWPOISON;
         return 0;
 }
 
 int copy_user_large_folio(struct folio *dst, struct folio *src,
                           unsigned long addr_hint, struct vm_area_struct *vma)
 {
         unsigned int nr_pages = folio_nr_pages(dst);
         struct copy_subpage_arg arg = {
                 .dst = dst,
                 .src = src,
                 .vma = vma,
         };
 
         if (unlikely(nr_pages > MAX_ORDER_NR_PAGES))
                 return copy_user_gigantic_page(dst, src, addr_hint, vma, nr_pages);
 
         return process_huge_page(addr_hint, nr_pages, copy_subpage, &arg);
 }
 
 long copy_folio_from_user(struct folio *dst_folio,
                            const void __user *usr_src,
                            bool allow_pagefault)
 {
         void *kaddr;
         unsigned long i, rc = 0;
         unsigned int nr_pages = folio_nr_pages(dst_folio);
         unsigned long ret_val = nr_pages * PAGE_SIZE;
         struct page *subpage;
 
         for (i = 0; i < nr_pages; i++) {
                 subpage = folio_page(dst_folio, i);
                 kaddr = kmap_local_page(subpage);
                 if (!allow_pagefault)
                         pagefault_disable();
                 rc = copy_from_user(kaddr, usr_src + i * PAGE_SIZE, PAGE_SIZE);
                 if (!allow_pagefault)
                         pagefault_enable();
                 kunmap_local(kaddr);
 
                 ret_val -= (PAGE_SIZE - rc);
                 if (rc)
                         break;
 
                 flush_dcache_page(subpage);
 
                 cond_resched();
         }
         return ret_val;
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
 #if USE_SPLIT_PTE_PTLOCKS && ALLOC_SPLIT_PTLOCKS
 
 static struct kmem_cache *page_ptl_cachep;
 
 void __init ptlock_cache_init(void)
 {
         page_ptl_cachep = kmem_cache_create("page->ptl", sizeof(spinlock_t), 0,
                         SLAB_PANIC, NULL);
 }
 
 bool ptlock_alloc(struct ptdesc *ptdesc)
 {
         spinlock_t *ptl;
 
         ptl = kmem_cache_alloc(page_ptl_cachep, GFP_KERNEL);
         if (!ptl)
                 return false;
         ptdesc->ptl = ptl;
         return true;
 }
 
 void ptlock_free(struct ptdesc *ptdesc)
 {
         kmem_cache_free(page_ptl_cachep, ptdesc->ptl);
 }
 #endif
 
 void vma_pgtable_walk_begin(struct vm_area_struct *vma)
 {
         if (is_vm_hugetlb_page(vma))
                 hugetlb_vma_lock_read(vma);
 }
 
 void vma_pgtable_walk_end(struct vm_area_struct *vma)
 {
         if (is_vm_hugetlb_page(vma))
                 hugetlb_vma_unlock_read(vma);
 }