TOMOYO Linux Cross Reference
Linux/arch/x86/xen/mmu_pv.c

   // SPDX-License-Identifier: GPL-2.0
   
   /*
    * Xen mmu operations
    *
    * This file contains the various mmu fetch and update operations.
    * The most important job they must perform is the mapping between the
    * domain's pfn and the overall machine mfns.
    *
   * Xen allows guests to directly update the pagetable, in a controlled
   * fashion.  In other words, the guest modifies the same pagetable
   * that the CPU actually uses, which eliminates the overhead of having
   * a separate shadow pagetable.
   *
   * In order to allow this, it falls on the guest domain to map its
   * notion of a "physical" pfn - which is just a domain-local linear
   * address - into a real "machine address" which the CPU's MMU can
   * use.
   *
   * A pgd_t/pmd_t/pte_t will typically contain an mfn, and so can be
   * inserted directly into the pagetable.  When creating a new
   * pte/pmd/pgd, it converts the passed pfn into an mfn.  Conversely,
   * when reading the content back with __(pgd|pmd|pte)_val, it converts
   * the mfn back into a pfn.
   *
   * The other constraint is that all pages which make up a pagetable
   * must be mapped read-only in the guest.  This prevents uncontrolled
   * guest updates to the pagetable.  Xen strictly enforces this, and
   * will disallow any pagetable update which will end up mapping a
   * pagetable page RW, and will disallow using any writable page as a
   * pagetable.
   *
   * Naively, when loading %cr3 with the base of a new pagetable, Xen
   * would need to validate the whole pagetable before going on.
   * Naturally, this is quite slow.  The solution is to "pin" a
   * pagetable, which enforces all the constraints on the pagetable even
   * when it is not actively in use.  This means that Xen can be assured
   * that it is still valid when you do load it into %cr3, and doesn't
   * need to revalidate it.
   *
   * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
   */
  #include <linux/sched/mm.h>
  #include <linux/debugfs.h>
  #include <linux/bug.h>
  #include <linux/vmalloc.h>
  #include <linux/export.h>
  #include <linux/init.h>
  #include <linux/gfp.h>
  #include <linux/memblock.h>
  #include <linux/seq_file.h>
  #include <linux/crash_dump.h>
  #include <linux/pgtable.h>
  #ifdef CONFIG_KEXEC_CORE
  #include <linux/kexec.h>
  #endif
  
  #include <trace/events/xen.h>
  
  #include <asm/tlbflush.h>
  #include <asm/fixmap.h>
  #include <asm/mmu_context.h>
  #include <asm/setup.h>
  #include <asm/paravirt.h>
  #include <asm/e820/api.h>
  #include <asm/linkage.h>
  #include <asm/page.h>
  #include <asm/init.h>
  #include <asm/memtype.h>
  #include <asm/smp.h>
  #include <asm/tlb.h>
  
  #include <asm/xen/hypercall.h>
  #include <asm/xen/hypervisor.h>
  
  #include <xen/xen.h>
  #include <xen/page.h>
  #include <xen/interface/xen.h>
  #include <xen/interface/hvm/hvm_op.h>
  #include <xen/interface/version.h>
  #include <xen/interface/memory.h>
  #include <xen/hvc-console.h>
  #include <xen/swiotlb-xen.h>
  
  #include "xen-ops.h"
  
  /*
   * Prototypes for functions called via PV_CALLEE_SAVE_REGS_THUNK() in order
   * to avoid warnings with "-Wmissing-prototypes".
   */
  pteval_t xen_pte_val(pte_t pte);
  pgdval_t xen_pgd_val(pgd_t pgd);
  pmdval_t xen_pmd_val(pmd_t pmd);
  pudval_t xen_pud_val(pud_t pud);
  p4dval_t xen_p4d_val(p4d_t p4d);
  pte_t xen_make_pte(pteval_t pte);
  pgd_t xen_make_pgd(pgdval_t pgd);
  pmd_t xen_make_pmd(pmdval_t pmd);
  pud_t xen_make_pud(pudval_t pud);
 p4d_t xen_make_p4d(p4dval_t p4d);
 pte_t xen_make_pte_init(pteval_t pte);
 
 #ifdef CONFIG_X86_VSYSCALL_EMULATION
 /* l3 pud for userspace vsyscall mapping */
 static pud_t level3_user_vsyscall[PTRS_PER_PUD] __page_aligned_bss;
 #endif
 
 /*
  * Protects atomic reservation decrease/increase against concurrent increases.
  * Also protects non-atomic updates of current_pages and balloon lists.
  */
 static DEFINE_SPINLOCK(xen_reservation_lock);
 
 /*
  * Note about cr3 (pagetable base) values:
  *
  * xen_cr3 contains the current logical cr3 value; it contains the
  * last set cr3.  This may not be the current effective cr3, because
  * its update may be being lazily deferred.  However, a vcpu looking
  * at its own cr3 can use this value knowing that it everything will
  * be self-consistent.
  *
  * xen_current_cr3 contains the actual vcpu cr3; it is set once the
  * hypercall to set the vcpu cr3 is complete (so it may be a little
  * out of date, but it will never be set early).  If one vcpu is
  * looking at another vcpu's cr3 value, it should use this variable.
  */
 DEFINE_PER_CPU(unsigned long, xen_cr3);  /* cr3 stored as physaddr */
 static DEFINE_PER_CPU(unsigned long, xen_current_cr3);  /* actual vcpu cr3 */
 
 static phys_addr_t xen_pt_base, xen_pt_size __initdata;
 
 static DEFINE_STATIC_KEY_FALSE(xen_struct_pages_ready);
 
 /*
  * Just beyond the highest usermode address.  STACK_TOP_MAX has a
  * redzone above it, so round it up to a PGD boundary.
  */
 #define USER_LIMIT      ((STACK_TOP_MAX + PGDIR_SIZE - 1) & PGDIR_MASK)
 
 void make_lowmem_page_readonly(void *vaddr)
 {
         pte_t *pte, ptev;
         unsigned long address = (unsigned long)vaddr;
         unsigned int level;
 
         pte = lookup_address(address, &level);
         if (pte == NULL)
                 return;         /* vaddr missing */
 
         ptev = pte_wrprotect(*pte);
 
         if (HYPERVISOR_update_va_mapping(address, ptev, 0))
                 BUG();
 }
 
 void make_lowmem_page_readwrite(void *vaddr)
 {
         pte_t *pte, ptev;
         unsigned long address = (unsigned long)vaddr;
         unsigned int level;
 
         pte = lookup_address(address, &level);
         if (pte == NULL)
                 return;         /* vaddr missing */
 
         ptev = pte_mkwrite_novma(*pte);
 
         if (HYPERVISOR_update_va_mapping(address, ptev, 0))
                 BUG();
 }
 
 
 /*
  * During early boot all page table pages are pinned, but we do not have struct
  * pages, so return true until struct pages are ready.
  */
 static bool xen_page_pinned(void *ptr)
 {
         if (static_branch_likely(&xen_struct_pages_ready)) {
                 struct page *page = virt_to_page(ptr);
 
                 return PagePinned(page);
         }
         return true;
 }
 
 static void xen_extend_mmu_update(const struct mmu_update *update)
 {
         struct multicall_space mcs;
         struct mmu_update *u;
 
         mcs = xen_mc_extend_args(__HYPERVISOR_mmu_update, sizeof(*u));
 
         if (mcs.mc != NULL) {
                 mcs.mc->args[1]++;
         } else {
                 mcs = __xen_mc_entry(sizeof(*u));
                 MULTI_mmu_update(mcs.mc, mcs.args, 1, NULL, DOMID_SELF);
         }
 
         u = mcs.args;
         *u = *update;
 }
 
 static void xen_extend_mmuext_op(const struct mmuext_op *op)
 {
         struct multicall_space mcs;
         struct mmuext_op *u;
 
         mcs = xen_mc_extend_args(__HYPERVISOR_mmuext_op, sizeof(*u));
 
         if (mcs.mc != NULL) {
                 mcs.mc->args[1]++;
         } else {
                 mcs = __xen_mc_entry(sizeof(*u));
                 MULTI_mmuext_op(mcs.mc, mcs.args, 1, NULL, DOMID_SELF);
         }
 
         u = mcs.args;
         *u = *op;
 }
 
 static void xen_set_pmd_hyper(pmd_t *ptr, pmd_t val)
 {
         struct mmu_update u;
 
         preempt_disable();
 
         xen_mc_batch();
 
         /* ptr may be ioremapped for 64-bit pagetable setup */
         u.ptr = arbitrary_virt_to_machine(ptr).maddr;
         u.val = pmd_val_ma(val);
         xen_extend_mmu_update(&u);
 
         xen_mc_issue(XEN_LAZY_MMU);
 
         preempt_enable();
 }
 
 static void xen_set_pmd(pmd_t *ptr, pmd_t val)
 {
         trace_xen_mmu_set_pmd(ptr, val);
 
         /* If page is not pinned, we can just update the entry
            directly */
         if (!xen_page_pinned(ptr)) {
                 *ptr = val;
                 return;
         }
 
         xen_set_pmd_hyper(ptr, val);
 }
 
 /*
  * Associate a virtual page frame with a given physical page frame
  * and protection flags for that frame.
  */
 void __init set_pte_mfn(unsigned long vaddr, unsigned long mfn, pgprot_t flags)
 {
         if (HYPERVISOR_update_va_mapping(vaddr, mfn_pte(mfn, flags),
                                          UVMF_INVLPG))
                 BUG();
 }
 
 static bool xen_batched_set_pte(pte_t *ptep, pte_t pteval)
 {
         struct mmu_update u;
 
         if (xen_get_lazy_mode() != XEN_LAZY_MMU)
                 return false;
 
         xen_mc_batch();
 
         u.ptr = virt_to_machine(ptep).maddr | MMU_NORMAL_PT_UPDATE;
         u.val = pte_val_ma(pteval);
         xen_extend_mmu_update(&u);
 
         xen_mc_issue(XEN_LAZY_MMU);
 
         return true;
 }
 
 static inline void __xen_set_pte(pte_t *ptep, pte_t pteval)
 {
         if (!xen_batched_set_pte(ptep, pteval)) {
                 /*
                  * Could call native_set_pte() here and trap and
                  * emulate the PTE write, but a hypercall is much cheaper.
                  */
                 struct mmu_update u;
 
                 u.ptr = virt_to_machine(ptep).maddr | MMU_NORMAL_PT_UPDATE;
                 u.val = pte_val_ma(pteval);
                 HYPERVISOR_mmu_update(&u, 1, NULL, DOMID_SELF);
         }
 }
 
 static void xen_set_pte(pte_t *ptep, pte_t pteval)
 {
         trace_xen_mmu_set_pte(ptep, pteval);
         __xen_set_pte(ptep, pteval);
 }
 
 static pte_t xen_ptep_modify_prot_start(struct vm_area_struct *vma,
                                         unsigned long addr, pte_t *ptep)
 {
         /* Just return the pte as-is.  We preserve the bits on commit */
         trace_xen_mmu_ptep_modify_prot_start(vma->vm_mm, addr, ptep, *ptep);
         return *ptep;
 }
 
 static void xen_ptep_modify_prot_commit(struct vm_area_struct *vma,
                                         unsigned long addr,
                                         pte_t *ptep, pte_t pte)
 {
         struct mmu_update u;
 
         trace_xen_mmu_ptep_modify_prot_commit(vma->vm_mm, addr, ptep, pte);
         xen_mc_batch();
 
         u.ptr = virt_to_machine(ptep).maddr | MMU_PT_UPDATE_PRESERVE_AD;
         u.val = pte_val_ma(pte);
         xen_extend_mmu_update(&u);
 
         xen_mc_issue(XEN_LAZY_MMU);
 }
 
 /* Assume pteval_t is equivalent to all the other *val_t types. */
 static pteval_t pte_mfn_to_pfn(pteval_t val)
 {
         if (val & _PAGE_PRESENT) {
                 unsigned long mfn = (val & XEN_PTE_MFN_MASK) >> PAGE_SHIFT;
                 unsigned long pfn = mfn_to_pfn(mfn);
 
                 pteval_t flags = val & PTE_FLAGS_MASK;
                 if (unlikely(pfn == ~0))
                         val = flags & ~_PAGE_PRESENT;
                 else
                         val = ((pteval_t)pfn << PAGE_SHIFT) | flags;
         }
 
         return val;
 }
 
 static pteval_t pte_pfn_to_mfn(pteval_t val)
 {
         if (val & _PAGE_PRESENT) {
                 unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
                 pteval_t flags = val & PTE_FLAGS_MASK;
                 unsigned long mfn;
 
                 mfn = __pfn_to_mfn(pfn);
 
                 /*
                  * If there's no mfn for the pfn, then just create an
                  * empty non-present pte.  Unfortunately this loses
                  * information about the original pfn, so
                  * pte_mfn_to_pfn is asymmetric.
                  */
                 if (unlikely(mfn == INVALID_P2M_ENTRY)) {
                         mfn = 0;
                         flags = 0;
                 } else
                         mfn &= ~(FOREIGN_FRAME_BIT | IDENTITY_FRAME_BIT);
                 val = ((pteval_t)mfn << PAGE_SHIFT) | flags;
         }
 
         return val;
 }
 
 __visible pteval_t xen_pte_val(pte_t pte)
 {
         pteval_t pteval = pte.pte;
 
         return pte_mfn_to_pfn(pteval);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_pte_val);
 
 __visible pgdval_t xen_pgd_val(pgd_t pgd)
 {
         return pte_mfn_to_pfn(pgd.pgd);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_pgd_val);
 
 __visible pte_t xen_make_pte(pteval_t pte)
 {
         pte = pte_pfn_to_mfn(pte);
 
         return native_make_pte(pte);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_make_pte);
 
 __visible pgd_t xen_make_pgd(pgdval_t pgd)
 {
         pgd = pte_pfn_to_mfn(pgd);
         return native_make_pgd(pgd);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_make_pgd);
 
 __visible pmdval_t xen_pmd_val(pmd_t pmd)
 {
         return pte_mfn_to_pfn(pmd.pmd);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_pmd_val);
 
 static void xen_set_pud_hyper(pud_t *ptr, pud_t val)
 {
         struct mmu_update u;
 
         preempt_disable();
 
         xen_mc_batch();
 
         /* ptr may be ioremapped for 64-bit pagetable setup */
         u.ptr = arbitrary_virt_to_machine(ptr).maddr;
         u.val = pud_val_ma(val);
         xen_extend_mmu_update(&u);
 
         xen_mc_issue(XEN_LAZY_MMU);
 
         preempt_enable();
 }
 
 static void xen_set_pud(pud_t *ptr, pud_t val)
 {
         trace_xen_mmu_set_pud(ptr, val);
 
         /* If page is not pinned, we can just update the entry
            directly */
         if (!xen_page_pinned(ptr)) {
                 *ptr = val;
                 return;
         }
 
         xen_set_pud_hyper(ptr, val);
 }
 
 __visible pmd_t xen_make_pmd(pmdval_t pmd)
 {
         pmd = pte_pfn_to_mfn(pmd);
         return native_make_pmd(pmd);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_make_pmd);
 
 __visible pudval_t xen_pud_val(pud_t pud)
 {
         return pte_mfn_to_pfn(pud.pud);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_pud_val);
 
 __visible pud_t xen_make_pud(pudval_t pud)
 {
         pud = pte_pfn_to_mfn(pud);
 
         return native_make_pud(pud);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_make_pud);
 
 static pgd_t *xen_get_user_pgd(pgd_t *pgd)
 {
         pgd_t *pgd_page = (pgd_t *)(((unsigned long)pgd) & PAGE_MASK);
         unsigned offset = pgd - pgd_page;
         pgd_t *user_ptr = NULL;
 
         if (offset < pgd_index(USER_LIMIT)) {
                 struct page *page = virt_to_page(pgd_page);
                 user_ptr = (pgd_t *)page->private;
                 if (user_ptr)
                         user_ptr += offset;
         }
 
         return user_ptr;
 }
 
 static void __xen_set_p4d_hyper(p4d_t *ptr, p4d_t val)
 {
         struct mmu_update u;
 
         u.ptr = virt_to_machine(ptr).maddr;
         u.val = p4d_val_ma(val);
         xen_extend_mmu_update(&u);
 }
 
 /*
  * Raw hypercall-based set_p4d, intended for in early boot before
  * there's a page structure.  This implies:
  *  1. The only existing pagetable is the kernel's
  *  2. It is always pinned
  *  3. It has no user pagetable attached to it
  */
 static void __init xen_set_p4d_hyper(p4d_t *ptr, p4d_t val)
 {
         preempt_disable();
 
         xen_mc_batch();
 
         __xen_set_p4d_hyper(ptr, val);
 
         xen_mc_issue(XEN_LAZY_MMU);
 
         preempt_enable();
 }
 
 static void xen_set_p4d(p4d_t *ptr, p4d_t val)
 {
         pgd_t *user_ptr = xen_get_user_pgd((pgd_t *)ptr);
         pgd_t pgd_val;
 
         trace_xen_mmu_set_p4d(ptr, (p4d_t *)user_ptr, val);
 
         /* If page is not pinned, we can just update the entry
            directly */
         if (!xen_page_pinned(ptr)) {
                 *ptr = val;
                 if (user_ptr) {
                         WARN_ON(xen_page_pinned(user_ptr));
                         pgd_val.pgd = p4d_val_ma(val);
                         *user_ptr = pgd_val;
                 }
                 return;
         }
 
         /* If it's pinned, then we can at least batch the kernel and
            user updates together. */
         xen_mc_batch();
 
         __xen_set_p4d_hyper(ptr, val);
         if (user_ptr)
                 __xen_set_p4d_hyper((p4d_t *)user_ptr, val);
 
         xen_mc_issue(XEN_LAZY_MMU);
 }
 
 #if CONFIG_PGTABLE_LEVELS >= 5
 __visible p4dval_t xen_p4d_val(p4d_t p4d)
 {
         return pte_mfn_to_pfn(p4d.p4d);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_p4d_val);
 
 __visible p4d_t xen_make_p4d(p4dval_t p4d)
 {
         p4d = pte_pfn_to_mfn(p4d);
 
         return native_make_p4d(p4d);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_make_p4d);
 #endif  /* CONFIG_PGTABLE_LEVELS >= 5 */
 
 static void xen_pmd_walk(struct mm_struct *mm, pmd_t *pmd,
                          void (*func)(struct mm_struct *mm, struct page *,
                                       enum pt_level),
                          bool last, unsigned long limit)
 {
         int i, nr;
 
         nr = last ? pmd_index(limit) + 1 : PTRS_PER_PMD;
         for (i = 0; i < nr; i++) {
                 if (!pmd_none(pmd[i]))
                         (*func)(mm, pmd_page(pmd[i]), PT_PTE);
         }
 }
 
 static void xen_pud_walk(struct mm_struct *mm, pud_t *pud,
                          void (*func)(struct mm_struct *mm, struct page *,
                                       enum pt_level),
                          bool last, unsigned long limit)
 {
         int i, nr;
 
         nr = last ? pud_index(limit) + 1 : PTRS_PER_PUD;
         for (i = 0; i < nr; i++) {
                 pmd_t *pmd;
 
                 if (pud_none(pud[i]))
                         continue;
 
                 pmd = pmd_offset(&pud[i], 0);
                 if (PTRS_PER_PMD > 1)
                         (*func)(mm, virt_to_page(pmd), PT_PMD);
                 xen_pmd_walk(mm, pmd, func, last && i == nr - 1, limit);
         }
 }
 
 static void xen_p4d_walk(struct mm_struct *mm, p4d_t *p4d,
                          void (*func)(struct mm_struct *mm, struct page *,
                                       enum pt_level),
                          bool last, unsigned long limit)
 {
         pud_t *pud;
 
 
         if (p4d_none(*p4d))
                 return;
 
         pud = pud_offset(p4d, 0);
         if (PTRS_PER_PUD > 1)
                 (*func)(mm, virt_to_page(pud), PT_PUD);
         xen_pud_walk(mm, pud, func, last, limit);
 }
 
 /*
  * (Yet another) pagetable walker.  This one is intended for pinning a
  * pagetable.  This means that it walks a pagetable and calls the
  * callback function on each page it finds making up the page table,
  * at every level.  It walks the entire pagetable, but it only bothers
  * pinning pte pages which are below limit.  In the normal case this
  * will be STACK_TOP_MAX, but at boot we need to pin up to
  * FIXADDR_TOP.
  *
  * We must skip the Xen hole in the middle of the address space, just after
  * the big x86-64 virtual hole.
  */
 static void __xen_pgd_walk(struct mm_struct *mm, pgd_t *pgd,
                            void (*func)(struct mm_struct *mm, struct page *,
                                         enum pt_level),
                            unsigned long limit)
 {
         int i, nr;
         unsigned hole_low = 0, hole_high = 0;
 
         /* The limit is the last byte to be touched */
         limit--;
         BUG_ON(limit >= FIXADDR_TOP);
 
         /*
          * 64-bit has a great big hole in the middle of the address
          * space, which contains the Xen mappings.
          */
         hole_low = pgd_index(GUARD_HOLE_BASE_ADDR);
         hole_high = pgd_index(GUARD_HOLE_END_ADDR);
 
         nr = pgd_index(limit) + 1;
         for (i = 0; i < nr; i++) {
                 p4d_t *p4d;
 
                 if (i >= hole_low && i < hole_high)
                         continue;
 
                 if (pgd_none(pgd[i]))
                         continue;
 
                 p4d = p4d_offset(&pgd[i], 0);
                 xen_p4d_walk(mm, p4d, func, i == nr - 1, limit);
         }
 
         /* Do the top level last, so that the callbacks can use it as
            a cue to do final things like tlb flushes. */
         (*func)(mm, virt_to_page(pgd), PT_PGD);
 }
 
 static void xen_pgd_walk(struct mm_struct *mm,
                          void (*func)(struct mm_struct *mm, struct page *,
                                       enum pt_level),
                          unsigned long limit)
 {
         __xen_pgd_walk(mm, mm->pgd, func, limit);
 }
 
 /* If we're using split pte locks, then take the page's lock and
    return a pointer to it.  Otherwise return NULL. */
 static spinlock_t *xen_pte_lock(struct page *page, struct mm_struct *mm)
 {
         spinlock_t *ptl = NULL;
 
 #if USE_SPLIT_PTE_PTLOCKS
         ptl = ptlock_ptr(page_ptdesc(page));
         spin_lock_nest_lock(ptl, &mm->page_table_lock);
 #endif
 
         return ptl;
 }
 
 static void xen_pte_unlock(void *v)
 {
         spinlock_t *ptl = v;
         spin_unlock(ptl);
 }
 
 static void xen_do_pin(unsigned level, unsigned long pfn)
 {
         struct mmuext_op op;
 
         op.cmd = level;
         op.arg1.mfn = pfn_to_mfn(pfn);
 
         xen_extend_mmuext_op(&op);
 }
 
 static void xen_pin_page(struct mm_struct *mm, struct page *page,
                          enum pt_level level)
 {
         unsigned pgfl = TestSetPagePinned(page);
 
         if (!pgfl) {
                 void *pt = lowmem_page_address(page);
                 unsigned long pfn = page_to_pfn(page);
                 struct multicall_space mcs = __xen_mc_entry(0);
                 spinlock_t *ptl;
 
                 /*
                  * We need to hold the pagetable lock between the time
                  * we make the pagetable RO and when we actually pin
                  * it.  If we don't, then other users may come in and
                  * attempt to update the pagetable by writing it,
                  * which will fail because the memory is RO but not
                  * pinned, so Xen won't do the trap'n'emulate.
                  *
                  * If we're using split pte locks, we can't hold the
                  * entire pagetable's worth of locks during the
                  * traverse, because we may wrap the preempt count (8
                  * bits).  The solution is to mark RO and pin each PTE
                  * page while holding the lock.  This means the number
                  * of locks we end up holding is never more than a
                  * batch size (~32 entries, at present).
                  *
                  * If we're not using split pte locks, we needn't pin
                  * the PTE pages independently, because we're
                  * protected by the overall pagetable lock.
                  */
                 ptl = NULL;
                 if (level == PT_PTE)
                         ptl = xen_pte_lock(page, mm);
 
                 MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
                                         pfn_pte(pfn, PAGE_KERNEL_RO),
                                         level == PT_PGD ? UVMF_TLB_FLUSH : 0);
 
                 if (ptl) {
                         xen_do_pin(MMUEXT_PIN_L1_TABLE, pfn);
 
                         /* Queue a deferred unlock for when this batch
                            is completed. */
                         xen_mc_callback(xen_pte_unlock, ptl);
                 }
         }
 }
 
 /* This is called just after a mm has been created, but it has not
    been used yet.  We need to make sure that its pagetable is all
    read-only, and can be pinned. */
 static void __xen_pgd_pin(struct mm_struct *mm, pgd_t *pgd)
 {
         pgd_t *user_pgd = xen_get_user_pgd(pgd);
 
         trace_xen_mmu_pgd_pin(mm, pgd);
 
         xen_mc_batch();
 
         __xen_pgd_walk(mm, pgd, xen_pin_page, USER_LIMIT);
 
         xen_do_pin(MMUEXT_PIN_L4_TABLE, PFN_DOWN(__pa(pgd)));
 
         if (user_pgd) {
                 xen_pin_page(mm, virt_to_page(user_pgd), PT_PGD);
                 xen_do_pin(MMUEXT_PIN_L4_TABLE,
                            PFN_DOWN(__pa(user_pgd)));
         }
 
         xen_mc_issue(0);
 }
 
 static void xen_pgd_pin(struct mm_struct *mm)
 {
         __xen_pgd_pin(mm, mm->pgd);
 }
 
 /*
  * On save, we need to pin all pagetables to make sure they get their
  * mfns turned into pfns.  Search the list for any unpinned pgds and pin
  * them (unpinned pgds are not currently in use, probably because the
  * process is under construction or destruction).
  *
  * Expected to be called in stop_machine() ("equivalent to taking
  * every spinlock in the system"), so the locking doesn't really
  * matter all that much.
  */
 void xen_mm_pin_all(void)
 {
         struct page *page;
 
         spin_lock(&pgd_lock);
 
         list_for_each_entry(page, &pgd_list, lru) {
                 if (!PagePinned(page)) {
                         __xen_pgd_pin(&init_mm, (pgd_t *)page_address(page));
                         SetPageSavePinned(page);
                 }
         }
 
         spin_unlock(&pgd_lock);
 }
 
 static void __init xen_mark_pinned(struct mm_struct *mm, struct page *page,
                                    enum pt_level level)
 {
         SetPagePinned(page);
 }
 
 /*
  * The init_mm pagetable is really pinned as soon as its created, but
  * that's before we have page structures to store the bits.  So do all
  * the book-keeping now once struct pages for allocated pages are
  * initialized. This happens only after memblock_free_all() is called.
  */
 static void __init xen_after_bootmem(void)
 {
         static_branch_enable(&xen_struct_pages_ready);
 #ifdef CONFIG_X86_VSYSCALL_EMULATION
         SetPagePinned(virt_to_page(level3_user_vsyscall));
 #endif
         xen_pgd_walk(&init_mm, xen_mark_pinned, FIXADDR_TOP);
 }
 
 static void xen_unpin_page(struct mm_struct *mm, struct page *page,
                            enum pt_level level)
 {
         unsigned pgfl = TestClearPagePinned(page);
 
         if (pgfl) {
                 void *pt = lowmem_page_address(page);
                 unsigned long pfn = page_to_pfn(page);
                 spinlock_t *ptl = NULL;
                 struct multicall_space mcs;
 
                 /*
                  * Do the converse to pin_page.  If we're using split
                  * pte locks, we must be holding the lock for while
                  * the pte page is unpinned but still RO to prevent
                  * concurrent updates from seeing it in this
                  * partially-pinned state.
                  */
                 if (level == PT_PTE) {
                         ptl = xen_pte_lock(page, mm);
 
                         if (ptl)
                                 xen_do_pin(MMUEXT_UNPIN_TABLE, pfn);
                 }
 
                 mcs = __xen_mc_entry(0);
 
                 MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
                                         pfn_pte(pfn, PAGE_KERNEL),
                                         level == PT_PGD ? UVMF_TLB_FLUSH : 0);
 
                 if (ptl) {
                         /* unlock when batch completed */
                         xen_mc_callback(xen_pte_unlock, ptl);
                 }
         }
 }
 
 /* Release a pagetables pages back as normal RW */
 static void __xen_pgd_unpin(struct mm_struct *mm, pgd_t *pgd)
 {
         pgd_t *user_pgd = xen_get_user_pgd(pgd);
 
         trace_xen_mmu_pgd_unpin(mm, pgd);
 
         xen_mc_batch();
 
         xen_do_pin(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));
 
         if (user_pgd) {
                 xen_do_pin(MMUEXT_UNPIN_TABLE,
                            PFN_DOWN(__pa(user_pgd)));
                 xen_unpin_page(mm, virt_to_page(user_pgd), PT_PGD);
         }
 
         __xen_pgd_walk(mm, pgd, xen_unpin_page, USER_LIMIT);
 
         xen_mc_issue(0);
 }
 
 static void xen_pgd_unpin(struct mm_struct *mm)
 {
         __xen_pgd_unpin(mm, mm->pgd);
 }
 
 /*
  * On resume, undo any pinning done at save, so that the rest of the
  * kernel doesn't see any unexpected pinned pagetables.
  */
 void xen_mm_unpin_all(void)
 {
         struct page *page;
 
         spin_lock(&pgd_lock);
 
         list_for_each_entry(page, &pgd_list, lru) {
                 if (PageSavePinned(page)) {
                         BUG_ON(!PagePinned(page));
                         __xen_pgd_unpin(&init_mm, (pgd_t *)page_address(page));
                         ClearPageSavePinned(page);
                 }
         }
 
         spin_unlock(&pgd_lock);
 }
 
 static void xen_enter_mmap(struct mm_struct *mm)
 {
         spin_lock(&mm->page_table_lock);
         xen_pgd_pin(mm);
         spin_unlock(&mm->page_table_lock);
 }
 
 static void drop_mm_ref_this_cpu(void *info)
 {
         struct mm_struct *mm = info;
 
         if (this_cpu_read(cpu_tlbstate.loaded_mm) == mm)
                 leave_mm();
 
         /*
          * If this cpu still has a stale cr3 reference, then make sure
          * it has been flushed.
          */
         if (this_cpu_read(xen_current_cr3) == __pa(mm->pgd))
                 xen_mc_flush();
 }
 
 #ifdef CONFIG_SMP
 /*
  * Another cpu may still have their %cr3 pointing at the pagetable, so
  * we need to repoint it somewhere else before we can unpin it.
  */
 static void xen_drop_mm_ref(struct mm_struct *mm)
 {
         cpumask_var_t mask;
         unsigned cpu;
 
         drop_mm_ref_this_cpu(mm);
 
         /* Get the "official" set of cpus referring to our pagetable. */
         if (!alloc_cpumask_var(&mask, GFP_ATOMIC)) {
                 for_each_online_cpu(cpu) {
                         if (per_cpu(xen_current_cr3, cpu) != __pa(mm->pgd))
                                 continue;
                         smp_call_function_single(cpu, drop_mm_ref_this_cpu, mm, 1);
                 }
                 return;
         }
 
         /*
          * It's possible that a vcpu may have a stale reference to our
          * cr3, because its in lazy mode, and it hasn't yet flushed
          * its set of pending hypercalls yet.  In this case, we can
          * look at its actual current cr3 value, and force it to flush
          * if needed.
          */
         cpumask_clear(mask);
         for_each_online_cpu(cpu) {
                 if (per_cpu(xen_current_cr3, cpu) == __pa(mm->pgd))
                         cpumask_set_cpu(cpu, mask);
         }
 
         smp_call_function_many(mask, drop_mm_ref_this_cpu, mm, 1);
         free_cpumask_var(mask);
 }
 #else
 static void xen_drop_mm_ref(struct mm_struct *mm)
 {
         drop_mm_ref_this_cpu(mm);
 }
 #endif
 
 /*
  * While a process runs, Xen pins its pagetables, which means that the
  * hypervisor forces it to be read-only, and it controls all updates
  * to it.  This means that all pagetable updates have to go via the
  * hypervisor, which is moderately expensive.
  *
  * Since we're pulling the pagetable down, we switch to use init_mm,
  * unpin old process pagetable and mark it all read-write, which
  * allows further operations on it to be simple memory accesses.
  *
  * The only subtle point is that another CPU may be still using the
  * pagetable because of lazy tlb flushing.  This means we need need to
  * switch all CPUs off this pagetable before we can unpin it.
  */
 static void xen_exit_mmap(struct mm_struct *mm)
 {
         get_cpu();              /* make sure we don't move around */
         xen_drop_mm_ref(mm);
         put_cpu();
 
         spin_lock(&mm->page_table_lock);
 
         /* pgd may not be pinned in the error exit path of execve */
         if (xen_page_pinned(mm->pgd))
                 xen_pgd_unpin(mm);
 
         spin_unlock(&mm->page_table_lock);
 }
 
 static void xen_post_allocator_init(void);
 
 static void __init pin_pagetable_pfn(unsigned cmd, unsigned long pfn)
 {
         struct mmuext_op op;
 
         op.cmd = cmd;
         op.arg1.mfn = pfn_to_mfn(pfn);
         if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF))
                 BUG();
 }
 
 static void __init xen_cleanhighmap(unsigned long vaddr,
                                     unsigned long vaddr_end)
 {
         unsigned long kernel_end = roundup((unsigned long)_brk_end, PMD_SIZE) - 1;
         pmd_t *pmd = level2_kernel_pgt + pmd_index(vaddr);
 
         /* NOTE: The loop is more greedy than the cleanup_highmap variant.
          * We include the PMD passed in on _both_ boundaries. */
         for (; vaddr <= vaddr_end && (pmd < (level2_kernel_pgt + PTRS_PER_PMD));
                         pmd++, vaddr += PMD_SIZE) {
                 if (pmd_none(*pmd))
                         continue;
                 if (vaddr < (unsigned long) _text || vaddr > kernel_end)
                         set_pmd(pmd, __pmd(0));
         }
         /* In case we did something silly, we should crash in this function
          * instead of somewhere later and be confusing. */
         xen_mc_flush();
 }
 
 /*
  * Make a page range writeable and free it.
  */
 static void __init xen_free_ro_pages(unsigned long paddr, unsigned long size)
 {
         void *vaddr = __va(paddr);
         void *vaddr_end = vaddr + size;
 
         for (; vaddr < vaddr_end; vaddr += PAGE_SIZE)
                 make_lowmem_page_readwrite(vaddr);
 
         memblock_phys_free(paddr, size);
 }
 
 static void __init xen_cleanmfnmap_free_pgtbl(void *pgtbl, bool unpin)
 {
         unsigned long pa = __pa(pgtbl) & PHYSICAL_PAGE_MASK;
 
         if (unpin)
                 pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(pa));
         ClearPagePinned(virt_to_page(__va(pa)));
         xen_free_ro_pages(pa, PAGE_SIZE);
 }
 
 static void __init xen_cleanmfnmap_pmd(pmd_t *pmd, bool unpin)
 {
         unsigned long pa;
         pte_t *pte_tbl;
         int i;
 
         if (pmd_leaf(*pmd)) {
                 pa = pmd_val(*pmd) & PHYSICAL_PAGE_MASK;
                 xen_free_ro_pages(pa, PMD_SIZE);
                 return;
         }
 
         pte_tbl = pte_offset_kernel(pmd, 0);
         for (i = 0; i < PTRS_PER_PTE; i++) {
                 if (pte_none(pte_tbl[i]))
                         continue;
                 pa = pte_pfn(pte_tbl[i]) << PAGE_SHIFT;
                 xen_free_ro_pages(pa, PAGE_SIZE);
         }
         set_pmd(pmd, __pmd(0));
         xen_cleanmfnmap_free_pgtbl(pte_tbl, unpin);
 }
 
 static void __init xen_cleanmfnmap_pud(pud_t *pud, bool unpin)
 {
         unsigned long pa;
         pmd_t *pmd_tbl;
         int i;
 
         if (pud_leaf(*pud)) {
                 pa = pud_val(*pud) & PHYSICAL_PAGE_MASK;
                 xen_free_ro_pages(pa, PUD_SIZE);
                 return;
         }
 
         pmd_tbl = pmd_offset(pud, 0);
         for (i = 0; i < PTRS_PER_PMD; i++) {
                 if (pmd_none(pmd_tbl[i]))
                         continue;
                 xen_cleanmfnmap_pmd(pmd_tbl + i, unpin);
         }
         set_pud(pud, __pud(0));
         xen_cleanmfnmap_free_pgtbl(pmd_tbl, unpin);
 }
 
 static void __init xen_cleanmfnmap_p4d(p4d_t *p4d, bool unpin)
 {
         unsigned long pa;
         pud_t *pud_tbl;
         int i;
 
         if (p4d_leaf(*p4d)) {
                 pa = p4d_val(*p4d) & PHYSICAL_PAGE_MASK;
                 xen_free_ro_pages(pa, P4D_SIZE);
                 return;
         }
 
         pud_tbl = pud_offset(p4d, 0);
         for (i = 0; i < PTRS_PER_PUD; i++) {
                 if (pud_none(pud_tbl[i]))
                         continue;
                 xen_cleanmfnmap_pud(pud_tbl + i, unpin);
         }
         set_p4d(p4d, __p4d(0));
         xen_cleanmfnmap_free_pgtbl(pud_tbl, unpin);
 }
 
 /*
  * Since it is well isolated we can (and since it is perhaps large we should)
  * also free the page tables mapping the initial P->M table.
  */
 static void __init xen_cleanmfnmap(unsigned long vaddr)
 {
         pgd_t *pgd;
         p4d_t *p4d;
         bool unpin;
 
         unpin = (vaddr == 2 * PGDIR_SIZE);
         vaddr &= PMD_MASK;
         pgd = pgd_offset_k(vaddr);
         p4d = p4d_offset(pgd, 0);
         if (!p4d_none(*p4d))
                 xen_cleanmfnmap_p4d(p4d, unpin);
 }
 
 static void __init xen_pagetable_p2m_free(void)
 {
         unsigned long size;
         unsigned long addr;
 
         size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
 
         /* No memory or already called. */
         if ((unsigned long)xen_p2m_addr == xen_start_info->mfn_list)
                 return;
 
         /* using __ka address and sticking INVALID_P2M_ENTRY! */
         memset((void *)xen_start_info->mfn_list, 0xff, size);
 
         addr = xen_start_info->mfn_list;
         /*
          * We could be in __ka space.
          * We roundup to the PMD, which means that if anybody at this stage is
          * using the __ka address of xen_start_info or
          * xen_start_info->shared_info they are in going to crash. Fortunately
          * we have already revectored in xen_setup_kernel_pagetable.
          */
         size = roundup(size, PMD_SIZE);
 
         if (addr >= __START_KERNEL_map) {
                 xen_cleanhighmap(addr, addr + size);
                 size = PAGE_ALIGN(xen_start_info->nr_pages *
                                   sizeof(unsigned long));
                 memblock_free((void *)addr, size);
         } else {
                 xen_cleanmfnmap(addr);
         }
 }
 
 static void __init xen_pagetable_cleanhighmap(void)
 {
         unsigned long size;
         unsigned long addr;
 
         /* At this stage, cleanup_highmap has already cleaned __ka space
          * from _brk_limit way up to the max_pfn_mapped (which is the end of
          * the ramdisk). We continue on, erasing PMD entries that point to page
          * tables - do note that they are accessible at this stage via __va.
          * As Xen is aligning the memory end to a 4MB boundary, for good
          * measure we also round up to PMD_SIZE * 2 - which means that if
          * anybody is using __ka address to the initial boot-stack - and try
          * to use it - they are going to crash. The xen_start_info has been
          * taken care of already in xen_setup_kernel_pagetable. */
         addr = xen_start_info->pt_base;
         size = xen_start_info->nr_pt_frames * PAGE_SIZE;
 
         xen_cleanhighmap(addr, roundup(addr + size, PMD_SIZE * 2));
         xen_start_info->pt_base = (unsigned long)__va(__pa(xen_start_info->pt_base));
 }
 
 static void __init xen_pagetable_p2m_setup(void)
 {
         xen_vmalloc_p2m_tree();
 
         xen_pagetable_p2m_free();
 
         xen_pagetable_cleanhighmap();
 
         /* And revector! Bye bye old array */
         xen_start_info->mfn_list = (unsigned long)xen_p2m_addr;
 }
 
 static void __init xen_pagetable_init(void)
 {
         /*
          * The majority of further PTE writes is to pagetables already
          * announced as such to Xen. Hence it is more efficient to use
          * hypercalls for these updates.
          */
         pv_ops.mmu.set_pte = __xen_set_pte;
 
         paging_init();
         xen_post_allocator_init();
 
         xen_pagetable_p2m_setup();
 
         /* Allocate and initialize top and mid mfn levels for p2m structure */
         xen_build_mfn_list_list();
 
         /* Remap memory freed due to conflicts with E820 map */
         xen_remap_memory();
         xen_setup_mfn_list_list();
 }
 
 static noinstr void xen_write_cr2(unsigned long cr2)
 {
         this_cpu_read(xen_vcpu)->arch.cr2 = cr2;
 }
 
 static noinline void xen_flush_tlb(void)
 {
         struct mmuext_op *op;
         struct multicall_space mcs;
 
         preempt_disable();
 
         mcs = xen_mc_entry(sizeof(*op));
 
         op = mcs.args;
         op->cmd = MMUEXT_TLB_FLUSH_LOCAL;
         MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
 
         xen_mc_issue(XEN_LAZY_MMU);
 
         preempt_enable();
 }
 
 static void xen_flush_tlb_one_user(unsigned long addr)
 {
         struct mmuext_op *op;
         struct multicall_space mcs;
 
         trace_xen_mmu_flush_tlb_one_user(addr);
 
         preempt_disable();
 
         mcs = xen_mc_entry(sizeof(*op));
         op = mcs.args;
         op->cmd = MMUEXT_INVLPG_LOCAL;
         op->arg1.linear_addr = addr & PAGE_MASK;
         MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
 
         xen_mc_issue(XEN_LAZY_MMU);
 
         preempt_enable();
 }
 
 static void xen_flush_tlb_multi(const struct cpumask *cpus,
                                 const struct flush_tlb_info *info)
 {
         struct {
                 struct mmuext_op op;
                 DECLARE_BITMAP(mask, NR_CPUS);
         } *args;
         struct multicall_space mcs;
         const size_t mc_entry_size = sizeof(args->op) +
                 sizeof(args->mask[0]) * BITS_TO_LONGS(num_possible_cpus());
 
         trace_xen_mmu_flush_tlb_multi(cpus, info->mm, info->start, info->end);
 
         if (cpumask_empty(cpus))
                 return;         /* nothing to do */
 
         mcs = xen_mc_entry(mc_entry_size);
         args = mcs.args;
         args->op.arg2.vcpumask = to_cpumask(args->mask);
 
         /* Remove any offline CPUs */
         cpumask_and(to_cpumask(args->mask), cpus, cpu_online_mask);
 
         args->op.cmd = MMUEXT_TLB_FLUSH_MULTI;
         if (info->end != TLB_FLUSH_ALL &&
             (info->end - info->start) <= PAGE_SIZE) {
                 args->op.cmd = MMUEXT_INVLPG_MULTI;
                 args->op.arg1.linear_addr = info->start;
         }
 
         MULTI_mmuext_op(mcs.mc, &args->op, 1, NULL, DOMID_SELF);
 
         xen_mc_issue(XEN_LAZY_MMU);
 }
 
 static unsigned long xen_read_cr3(void)
 {
         return this_cpu_read(xen_cr3);
 }
 
 static void set_current_cr3(void *v)
 {
         this_cpu_write(xen_current_cr3, (unsigned long)v);
 }
 
 static void __xen_write_cr3(bool kernel, unsigned long cr3)
 {
         struct mmuext_op op;
         unsigned long mfn;
 
         trace_xen_mmu_write_cr3(kernel, cr3);
 
         if (cr3)
                 mfn = pfn_to_mfn(PFN_DOWN(cr3));
         else
                 mfn = 0;
 
         WARN_ON(mfn == 0 && kernel);
 
         op.cmd = kernel ? MMUEXT_NEW_BASEPTR : MMUEXT_NEW_USER_BASEPTR;
         op.arg1.mfn = mfn;
 
         xen_extend_mmuext_op(&op);
 
         if (kernel) {
                 this_cpu_write(xen_cr3, cr3);
 
                 /* Update xen_current_cr3 once the batch has actually
                    been submitted. */
                 xen_mc_callback(set_current_cr3, (void *)cr3);
         }
 }
 static void xen_write_cr3(unsigned long cr3)
 {
         pgd_t *user_pgd = xen_get_user_pgd(__va(cr3));
 
         BUG_ON(preemptible());
 
         xen_mc_batch();  /* disables interrupts */
 
         /* Update while interrupts are disabled, so its atomic with
            respect to ipis */
         this_cpu_write(xen_cr3, cr3);
 
         __xen_write_cr3(true, cr3);
 
         if (user_pgd)
                 __xen_write_cr3(false, __pa(user_pgd));
         else
                 __xen_write_cr3(false, 0);
 
         xen_mc_issue(XEN_LAZY_CPU);  /* interrupts restored */
 }
 
 /*
  * At the start of the day - when Xen launches a guest, it has already
  * built pagetables for the guest. We diligently look over them
  * in xen_setup_kernel_pagetable and graft as appropriate them in the
  * init_top_pgt and its friends. Then when we are happy we load
  * the new init_top_pgt - and continue on.
  *
  * The generic code starts (start_kernel) and 'init_mem_mapping' sets
  * up the rest of the pagetables. When it has completed it loads the cr3.
  * N.B. that baremetal would start at 'start_kernel' (and the early
  * #PF handler would create bootstrap pagetables) - so we are running
  * with the same assumptions as what to do when write_cr3 is executed
  * at this point.
  *
  * Since there are no user-page tables at all, we have two variants
  * of xen_write_cr3 - the early bootup (this one), and the late one
  * (xen_write_cr3). The reason we have to do that is that in 64-bit
  * the Linux kernel and user-space are both in ring 3 while the
  * hypervisor is in ring 0.
  */
 static void __init xen_write_cr3_init(unsigned long cr3)
 {
         BUG_ON(preemptible());
 
         xen_mc_batch();  /* disables interrupts */
 
         /* Update while interrupts are disabled, so its atomic with
            respect to ipis */
         this_cpu_write(xen_cr3, cr3);
 
         __xen_write_cr3(true, cr3);
 
         xen_mc_issue(XEN_LAZY_CPU);  /* interrupts restored */
 }
 
 static int xen_pgd_alloc(struct mm_struct *mm)
 {
         pgd_t *pgd = mm->pgd;
         struct page *page = virt_to_page(pgd);
         pgd_t *user_pgd;
         int ret = -ENOMEM;
 
         BUG_ON(PagePinned(virt_to_page(pgd)));
         BUG_ON(page->private != 0);
 
         user_pgd = (pgd_t *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
         page->private = (unsigned long)user_pgd;
 
         if (user_pgd != NULL) {
 #ifdef CONFIG_X86_VSYSCALL_EMULATION
                 user_pgd[pgd_index(VSYSCALL_ADDR)] =
                         __pgd(__pa(level3_user_vsyscall) | _PAGE_TABLE);
 #endif
                 ret = 0;
         }
 
         BUG_ON(PagePinned(virt_to_page(xen_get_user_pgd(pgd))));
 
         return ret;
 }
 
 static void xen_pgd_free(struct mm_struct *mm, pgd_t *pgd)
 {
         pgd_t *user_pgd = xen_get_user_pgd(pgd);
 
         if (user_pgd)
                 free_page((unsigned long)user_pgd);
 }
 
 /*
  * Init-time set_pte while constructing initial pagetables, which
  * doesn't allow RO page table pages to be remapped RW.
  *
  * If there is no MFN for this PFN then this page is initially
  * ballooned out so clear the PTE (as in decrease_reservation() in
  * drivers/xen/balloon.c).
  *
  * Many of these PTE updates are done on unpinned and writable pages
  * and doing a hypercall for these is unnecessary and expensive.  At
  * this point it is rarely possible to tell if a page is pinned, so
  * mostly write the PTE directly and rely on Xen trapping and
  * emulating any updates as necessary.
  */
 static void __init xen_set_pte_init(pte_t *ptep, pte_t pte)
 {
         if (unlikely(is_early_ioremap_ptep(ptep)))
                 __xen_set_pte(ptep, pte);
         else
                 native_set_pte(ptep, pte);
 }
 
 __visible pte_t xen_make_pte_init(pteval_t pte)
 {
         unsigned long pfn;
 
         /*
          * Pages belonging to the initial p2m list mapped outside the default
          * address range must be mapped read-only. This region contains the
          * page tables for mapping the p2m list, too, and page tables MUST be
          * mapped read-only.
          */
         pfn = (pte & PTE_PFN_MASK) >> PAGE_SHIFT;
         if (xen_start_info->mfn_list < __START_KERNEL_map &&
             pfn >= xen_start_info->first_p2m_pfn &&
             pfn < xen_start_info->first_p2m_pfn + xen_start_info->nr_p2m_frames)
                 pte &= ~_PAGE_RW;
 
         pte = pte_pfn_to_mfn(pte);
         return native_make_pte(pte);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_make_pte_init);
 
 /* Early in boot, while setting up the initial pagetable, assume
    everything is pinned. */
 static void __init xen_alloc_pte_init(struct mm_struct *mm, unsigned long pfn)
 {
 #ifdef CONFIG_FLATMEM
         BUG_ON(mem_map);        /* should only be used early */
 #endif
         make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
         pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE, pfn);
 }
 
 /* Used for pmd and pud */
 static void __init xen_alloc_pmd_init(struct mm_struct *mm, unsigned long pfn)
 {
 #ifdef CONFIG_FLATMEM
         BUG_ON(mem_map);        /* should only be used early */
 #endif
         make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
 }
 
 /* Early release_pte assumes that all pts are pinned, since there's
    only init_mm and anything attached to that is pinned. */
 static void __init xen_release_pte_init(unsigned long pfn)
 {
         pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, pfn);
         make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
 }
 
 static void __init xen_release_pmd_init(unsigned long pfn)
 {
         make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
 }
 
 static inline void __pin_pagetable_pfn(unsigned cmd, unsigned long pfn)
 {
         struct multicall_space mcs;
         struct mmuext_op *op;
 
         mcs = __xen_mc_entry(sizeof(*op));
         op = mcs.args;
         op->cmd = cmd;
         op->arg1.mfn = pfn_to_mfn(pfn);
 
         MULTI_mmuext_op(mcs.mc, mcs.args, 1, NULL, DOMID_SELF);
 }
 
 static inline void __set_pfn_prot(unsigned long pfn, pgprot_t prot)
 {
         struct multicall_space mcs;
         unsigned long addr = (unsigned long)__va(pfn << PAGE_SHIFT);
 
         mcs = __xen_mc_entry(0);
         MULTI_update_va_mapping(mcs.mc, (unsigned long)addr,
                                 pfn_pte(pfn, prot), 0);
 }
 
 /* This needs to make sure the new pte page is pinned iff its being
    attached to a pinned pagetable. */
 static inline void xen_alloc_ptpage(struct mm_struct *mm, unsigned long pfn,
                                     unsigned level)
 {
         bool pinned = xen_page_pinned(mm->pgd);
 
         trace_xen_mmu_alloc_ptpage(mm, pfn, level, pinned);
 
         if (pinned) {
                 struct page *page = pfn_to_page(pfn);
 
                 pinned = false;
                 if (static_branch_likely(&xen_struct_pages_ready)) {
                         pinned = PagePinned(page);
                         SetPagePinned(page);
                 }
 
                 xen_mc_batch();
 
                 __set_pfn_prot(pfn, PAGE_KERNEL_RO);
 
                 if (level == PT_PTE && USE_SPLIT_PTE_PTLOCKS && !pinned)
                         __pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE, pfn);
 
                 xen_mc_issue(XEN_LAZY_MMU);
         }
 }
 
 static void xen_alloc_pte(struct mm_struct *mm, unsigned long pfn)
 {
         xen_alloc_ptpage(mm, pfn, PT_PTE);
 }
 
 static void xen_alloc_pmd(struct mm_struct *mm, unsigned long pfn)
 {
         xen_alloc_ptpage(mm, pfn, PT_PMD);
 }
 
 /* This should never happen until we're OK to use struct page */
 static inline void xen_release_ptpage(unsigned long pfn, unsigned level)
 {
         struct page *page = pfn_to_page(pfn);
         bool pinned = PagePinned(page);
 
         trace_xen_mmu_release_ptpage(pfn, level, pinned);
 
         if (pinned) {
                 xen_mc_batch();
 
                 if (level == PT_PTE && USE_SPLIT_PTE_PTLOCKS)
                         __pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, pfn);
 
                 __set_pfn_prot(pfn, PAGE_KERNEL);
 
                 xen_mc_issue(XEN_LAZY_MMU);
 
                 ClearPagePinned(page);
         }
 }
 
 static void xen_release_pte(unsigned long pfn)
 {
         xen_release_ptpage(pfn, PT_PTE);
 }
 
 static void xen_release_pmd(unsigned long pfn)
 {
         xen_release_ptpage(pfn, PT_PMD);
 }
 
 static void xen_alloc_pud(struct mm_struct *mm, unsigned long pfn)
 {
         xen_alloc_ptpage(mm, pfn, PT_PUD);
 }
 
 static void xen_release_pud(unsigned long pfn)
 {
         xen_release_ptpage(pfn, PT_PUD);
 }
 
 /*
  * Like __va(), but returns address in the kernel mapping (which is
  * all we have until the physical memory mapping has been set up.
  */
 static void * __init __ka(phys_addr_t paddr)
 {
         return (void *)(paddr + __START_KERNEL_map);
 }
 
 /* Convert a machine address to physical address */
 static unsigned long __init m2p(phys_addr_t maddr)
 {
         phys_addr_t paddr;
 
         maddr &= XEN_PTE_MFN_MASK;
         paddr = mfn_to_pfn(maddr >> PAGE_SHIFT) << PAGE_SHIFT;
 
         return paddr;
 }
 
 /* Convert a machine address to kernel virtual */
 static void * __init m2v(phys_addr_t maddr)
 {
         return __ka(m2p(maddr));
 }
 
 /* Set the page permissions on an identity-mapped pages */
 static void __init set_page_prot_flags(void *addr, pgprot_t prot,
                                        unsigned long flags)
 {
         unsigned long pfn = __pa(addr) >> PAGE_SHIFT;
         pte_t pte = pfn_pte(pfn, prot);
 
         if (HYPERVISOR_update_va_mapping((unsigned long)addr, pte, flags))
                 BUG();
 }
 static void __init set_page_prot(void *addr, pgprot_t prot)
 {
         return set_page_prot_flags(addr, prot, UVMF_NONE);
 }
 
 void __init xen_setup_machphys_mapping(void)
 {
         struct xen_machphys_mapping mapping;
 
         if (HYPERVISOR_memory_op(XENMEM_machphys_mapping, &mapping) == 0) {
                 machine_to_phys_mapping = (unsigned long *)mapping.v_start;
                 machine_to_phys_nr = mapping.max_mfn + 1;
         } else {
                 machine_to_phys_nr = MACH2PHYS_NR_ENTRIES;
         }
 }
 
 static void __init convert_pfn_mfn(void *v)
 {
         pte_t *pte = v;
         int i;
 
         /* All levels are converted the same way, so just treat them
            as ptes. */
         for (i = 0; i < PTRS_PER_PTE; i++)
                 pte[i] = xen_make_pte(pte[i].pte);
 }
 static void __init check_pt_base(unsigned long *pt_base, unsigned long *pt_end,
                                  unsigned long addr)
 {
         if (*pt_base == PFN_DOWN(__pa(addr))) {
                 set_page_prot_flags((void *)addr, PAGE_KERNEL, UVMF_INVLPG);
                 clear_page((void *)addr);
                 (*pt_base)++;
         }
         if (*pt_end == PFN_DOWN(__pa(addr))) {
                 set_page_prot_flags((void *)addr, PAGE_KERNEL, UVMF_INVLPG);
                 clear_page((void *)addr);
                 (*pt_end)--;
         }
 }
 /*
  * Set up the initial kernel pagetable.
  *
  * We can construct this by grafting the Xen provided pagetable into
  * head_64.S's preconstructed pagetables.  We copy the Xen L2's into
  * level2_ident_pgt, and level2_kernel_pgt.  This means that only the
  * kernel has a physical mapping to start with - but that's enough to
  * get __va working.  We need to fill in the rest of the physical
  * mapping once some sort of allocator has been set up.
  */
 void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
 {
         pud_t *l3;
         pmd_t *l2;
         unsigned long addr[3];
         unsigned long pt_base, pt_end;
         unsigned i;
 
         /* max_pfn_mapped is the last pfn mapped in the initial memory
          * mappings. Considering that on Xen after the kernel mappings we
          * have the mappings of some pages that don't exist in pfn space, we
          * set max_pfn_mapped to the last real pfn mapped. */
         if (xen_start_info->mfn_list < __START_KERNEL_map)
                 max_pfn_mapped = xen_start_info->first_p2m_pfn;
         else
                 max_pfn_mapped = PFN_DOWN(__pa(xen_start_info->mfn_list));
 
         pt_base = PFN_DOWN(__pa(xen_start_info->pt_base));
         pt_end = pt_base + xen_start_info->nr_pt_frames;
 
         /* Zap identity mapping */
         init_top_pgt[0] = __pgd(0);
 
         /* Pre-constructed entries are in pfn, so convert to mfn */
         /* L4[273] -> level3_ident_pgt  */
         /* L4[511] -> level3_kernel_pgt */
         convert_pfn_mfn(init_top_pgt);
 
         /* L3_i[0] -> level2_ident_pgt */
         convert_pfn_mfn(level3_ident_pgt);
         /* L3_k[510] -> level2_kernel_pgt */
         /* L3_k[511] -> level2_fixmap_pgt */
         convert_pfn_mfn(level3_kernel_pgt);
 
         /* L3_k[511][508-FIXMAP_PMD_NUM ... 507] -> level1_fixmap_pgt */
         convert_pfn_mfn(level2_fixmap_pgt);
 
         /* We get [511][511] and have Xen's version of level2_kernel_pgt */
         l3 = m2v(pgd[pgd_index(__START_KERNEL_map)].pgd);
         l2 = m2v(l3[pud_index(__START_KERNEL_map)].pud);
 
         addr[0] = (unsigned long)pgd;
         addr[1] = (unsigned long)l3;
         addr[2] = (unsigned long)l2;
         /* Graft it onto L4[273][0]. Note that we creating an aliasing problem:
          * Both L4[273][0] and L4[511][510] have entries that point to the same
          * L2 (PMD) tables. Meaning that if you modify it in __va space
          * it will be also modified in the __ka space! (But if you just
          * modify the PMD table to point to other PTE's or none, then you
          * are OK - which is what cleanup_highmap does) */
         copy_page(level2_ident_pgt, l2);
         /* Graft it onto L4[511][510] */
         copy_page(level2_kernel_pgt, l2);
 
         /*
          * Zap execute permission from the ident map. Due to the sharing of
          * L1 entries we need to do this in the L2.
          */
         if (__supported_pte_mask & _PAGE_NX) {
                 for (i = 0; i < PTRS_PER_PMD; ++i) {
                         if (pmd_none(level2_ident_pgt[i]))
                                 continue;
                         level2_ident_pgt[i] = pmd_set_flags(level2_ident_pgt[i], _PAGE_NX);
                 }
         }
 
         /* Copy the initial P->M table mappings if necessary. */
         i = pgd_index(xen_start_info->mfn_list);
         if (i && i < pgd_index(__START_KERNEL_map))
                 init_top_pgt[i] = ((pgd_t *)xen_start_info->pt_base)[i];
 
         /* Make pagetable pieces RO */
         set_page_prot(init_top_pgt, PAGE_KERNEL_RO);
         set_page_prot(level3_ident_pgt, PAGE_KERNEL_RO);
         set_page_prot(level3_kernel_pgt, PAGE_KERNEL_RO);
         set_page_prot(level2_ident_pgt, PAGE_KERNEL_RO);
         set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO);
         set_page_prot(level2_fixmap_pgt, PAGE_KERNEL_RO);
 
         for (i = 0; i < FIXMAP_PMD_NUM; i++) {
                 set_page_prot(level1_fixmap_pgt + i * PTRS_PER_PTE,
                               PAGE_KERNEL_RO);
         }
 
         /* Pin down new L4 */
         pin_pagetable_pfn(MMUEXT_PIN_L4_TABLE,
                           PFN_DOWN(__pa_symbol(init_top_pgt)));
 
         /* Unpin Xen-provided one */
         pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));
 
 #ifdef CONFIG_X86_VSYSCALL_EMULATION
         /* Pin user vsyscall L3 */
         set_page_prot(level3_user_vsyscall, PAGE_KERNEL_RO);
         pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE,
                           PFN_DOWN(__pa_symbol(level3_user_vsyscall)));
 #endif
 
         /*
          * At this stage there can be no user pgd, and no page structure to
          * attach it to, so make sure we just set kernel pgd.
          */
         xen_mc_batch();
         __xen_write_cr3(true, __pa(init_top_pgt));
         xen_mc_issue(XEN_LAZY_CPU);
 
         /* We can't that easily rip out L3 and L2, as the Xen pagetables are
          * set out this way: [L4], [L1], [L2], [L3], [L1], [L1] ...  for
          * the initial domain. For guests using the toolstack, they are in:
          * [L4], [L3], [L2], [L1], [L1], order .. So for dom0 we can only
          * rip out the [L4] (pgd), but for guests we shave off three pages.
          */
         for (i = 0; i < ARRAY_SIZE(addr); i++)
                 check_pt_base(&pt_base, &pt_end, addr[i]);
 
         /* Our (by three pages) smaller Xen pagetable that we are using */
         xen_pt_base = PFN_PHYS(pt_base);
         xen_pt_size = (pt_end - pt_base) * PAGE_SIZE;
         memblock_reserve(xen_pt_base, xen_pt_size);
 
         /* Revector the xen_start_info */
         xen_start_info = (struct start_info *)__va(__pa(xen_start_info));
 }
 
 /*
  * Read a value from a physical address.
  */
 static unsigned long __init xen_read_phys_ulong(phys_addr_t addr)
 {
         unsigned long *vaddr;
         unsigned long val;
 
         vaddr = early_memremap_ro(addr, sizeof(val));
         val = *vaddr;
         early_memunmap(vaddr, sizeof(val));
         return val;
 }
 
 /*
  * Translate a virtual address to a physical one without relying on mapped
  * page tables. Don't rely on big pages being aligned in (guest) physical
  * space!
  */
 static phys_addr_t __init xen_early_virt_to_phys(unsigned long vaddr)
 {
         phys_addr_t pa;
         pgd_t pgd;
         pud_t pud;
         pmd_t pmd;
         pte_t pte;
 
         pa = read_cr3_pa();
         pgd = native_make_pgd(xen_read_phys_ulong(pa + pgd_index(vaddr) *
                                                        sizeof(pgd)));
         if (!pgd_present(pgd))
                 return 0;
 
         pa = pgd_val(pgd) & PTE_PFN_MASK;
         pud = native_make_pud(xen_read_phys_ulong(pa + pud_index(vaddr) *
                                                        sizeof(pud)));
         if (!pud_present(pud))
                 return 0;
         pa = pud_val(pud) & PTE_PFN_MASK;
         if (pud_leaf(pud))
                 return pa + (vaddr & ~PUD_MASK);
 
         pmd = native_make_pmd(xen_read_phys_ulong(pa + pmd_index(vaddr) *
                                                        sizeof(pmd)));
         if (!pmd_present(pmd))
                 return 0;
         pa = pmd_val(pmd) & PTE_PFN_MASK;
         if (pmd_leaf(pmd))
                 return pa + (vaddr & ~PMD_MASK);
 
         pte = native_make_pte(xen_read_phys_ulong(pa + pte_index(vaddr) *
                                                        sizeof(pte)));
         if (!pte_present(pte))
                 return 0;
         pa = pte_pfn(pte) << PAGE_SHIFT;
 
         return pa | (vaddr & ~PAGE_MASK);
 }
 
 /*
  * Find a new area for the hypervisor supplied p2m list and relocate the p2m to
  * this area.
  */
 void __init xen_relocate_p2m(void)
 {
         phys_addr_t size, new_area, pt_phys, pmd_phys, pud_phys;
         unsigned long p2m_pfn, p2m_pfn_end, n_frames, pfn, pfn_end;
         int n_pte, n_pt, n_pmd, n_pud, idx_pte, idx_pt, idx_pmd, idx_pud;
         pte_t *pt;
         pmd_t *pmd;
         pud_t *pud;
         pgd_t *pgd;
         unsigned long *new_p2m;
 
         size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
         n_pte = roundup(size, PAGE_SIZE) >> PAGE_SHIFT;
         n_pt = roundup(size, PMD_SIZE) >> PMD_SHIFT;
         n_pmd = roundup(size, PUD_SIZE) >> PUD_SHIFT;
         n_pud = roundup(size, P4D_SIZE) >> P4D_SHIFT;
         n_frames = n_pte + n_pt + n_pmd + n_pud;
 
         new_area = xen_find_free_area(PFN_PHYS(n_frames));
         if (!new_area) {
                 xen_raw_console_write("Can't find new memory area for p2m needed due to E820 map conflict\n");
                 BUG();
         }
 
         /*
          * Setup the page tables for addressing the new p2m list.
          * We have asked the hypervisor to map the p2m list at the user address
          * PUD_SIZE. It may have done so, or it may have used a kernel space
          * address depending on the Xen version.
          * To avoid any possible virtual address collision, just use
          * 2 * PUD_SIZE for the new area.
          */
         pud_phys = new_area;
         pmd_phys = pud_phys + PFN_PHYS(n_pud);
         pt_phys = pmd_phys + PFN_PHYS(n_pmd);
         p2m_pfn = PFN_DOWN(pt_phys) + n_pt;
 
         pgd = __va(read_cr3_pa());
         new_p2m = (unsigned long *)(2 * PGDIR_SIZE);
         for (idx_pud = 0; idx_pud < n_pud; idx_pud++) {
                 pud = early_memremap(pud_phys, PAGE_SIZE);
                 clear_page(pud);
                 for (idx_pmd = 0; idx_pmd < min(n_pmd, PTRS_PER_PUD);
                                 idx_pmd++) {
                         pmd = early_memremap(pmd_phys, PAGE_SIZE);
                         clear_page(pmd);
                         for (idx_pt = 0; idx_pt < min(n_pt, PTRS_PER_PMD);
                                         idx_pt++) {
                                 pt = early_memremap(pt_phys, PAGE_SIZE);
                                 clear_page(pt);
                                 for (idx_pte = 0;
                                      idx_pte < min(n_pte, PTRS_PER_PTE);
                                      idx_pte++) {
                                         pt[idx_pte] = pfn_pte(p2m_pfn,
                                                               PAGE_KERNEL);
                                         p2m_pfn++;
                                 }
                                 n_pte -= PTRS_PER_PTE;
                                 early_memunmap(pt, PAGE_SIZE);
                                 make_lowmem_page_readonly(__va(pt_phys));
                                 pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE,
                                                 PFN_DOWN(pt_phys));
                                 pmd[idx_pt] = __pmd(_PAGE_TABLE | pt_phys);
                                 pt_phys += PAGE_SIZE;
                         }
                         n_pt -= PTRS_PER_PMD;
                         early_memunmap(pmd, PAGE_SIZE);
                         make_lowmem_page_readonly(__va(pmd_phys));
                         pin_pagetable_pfn(MMUEXT_PIN_L2_TABLE,
                                         PFN_DOWN(pmd_phys));
                         pud[idx_pmd] = __pud(_PAGE_TABLE | pmd_phys);
                         pmd_phys += PAGE_SIZE;
                 }
                 n_pmd -= PTRS_PER_PUD;
                 early_memunmap(pud, PAGE_SIZE);
                 make_lowmem_page_readonly(__va(pud_phys));
                 pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE, PFN_DOWN(pud_phys));
                 set_pgd(pgd + 2 + idx_pud, __pgd(_PAGE_TABLE | pud_phys));
                 pud_phys += PAGE_SIZE;
         }
 
         /* Now copy the old p2m info to the new area. */
         memcpy(new_p2m, xen_p2m_addr, size);
         xen_p2m_addr = new_p2m;
 
         /* Release the old p2m list and set new list info. */
         p2m_pfn = PFN_DOWN(xen_early_virt_to_phys(xen_start_info->mfn_list));
         BUG_ON(!p2m_pfn);
         p2m_pfn_end = p2m_pfn + PFN_DOWN(size);
 
         if (xen_start_info->mfn_list < __START_KERNEL_map) {
                 pfn = xen_start_info->first_p2m_pfn;
                 pfn_end = xen_start_info->first_p2m_pfn +
                           xen_start_info->nr_p2m_frames;
                 set_pgd(pgd + 1, __pgd(0));
         } else {
                 pfn = p2m_pfn;
                 pfn_end = p2m_pfn_end;
         }
 
         memblock_phys_free(PFN_PHYS(pfn), PAGE_SIZE * (pfn_end - pfn));
         while (pfn < pfn_end) {
                 if (pfn == p2m_pfn) {
                         pfn = p2m_pfn_end;
                         continue;
                 }
                 make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
                 pfn++;
         }
 
         xen_start_info->mfn_list = (unsigned long)xen_p2m_addr;
         xen_start_info->first_p2m_pfn =  PFN_DOWN(new_area);
         xen_start_info->nr_p2m_frames = n_frames;
 }
 
 void __init xen_reserve_special_pages(void)
 {
         phys_addr_t paddr;
 
         memblock_reserve(__pa(xen_start_info), PAGE_SIZE);
         if (xen_start_info->store_mfn) {
                 paddr = PFN_PHYS(mfn_to_pfn(xen_start_info->store_mfn));
                 memblock_reserve(paddr, PAGE_SIZE);
         }
         if (!xen_initial_domain()) {
                 paddr = PFN_PHYS(mfn_to_pfn(xen_start_info->console.domU.mfn));
                 memblock_reserve(paddr, PAGE_SIZE);
         }
 }
 
 void __init xen_pt_check_e820(void)
 {
         if (xen_is_e820_reserved(xen_pt_base, xen_pt_size)) {
                 xen_raw_console_write("Xen hypervisor allocated page table memory conflicts with E820 map\n");
                 BUG();
         }
 }
 
 static unsigned char dummy_mapping[PAGE_SIZE] __page_aligned_bss;
 
 static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
 {
         pte_t pte;
         unsigned long vaddr;
 
         phys >>= PAGE_SHIFT;
 
         switch (idx) {
         case FIX_BTMAP_END ... FIX_BTMAP_BEGIN:
 #ifdef CONFIG_X86_VSYSCALL_EMULATION
         case VSYSCALL_PAGE:
 #endif
                 /* All local page mappings */
                 pte = pfn_pte(phys, prot);
                 break;
 
 #ifdef CONFIG_X86_LOCAL_APIC
         case FIX_APIC_BASE:     /* maps dummy local APIC */
                 pte = pfn_pte(PFN_DOWN(__pa(dummy_mapping)), PAGE_KERNEL);
                 break;
 #endif
 
 #ifdef CONFIG_X86_IO_APIC
         case FIX_IO_APIC_BASE_0 ... FIX_IO_APIC_BASE_END:
                 /*
                  * We just don't map the IO APIC - all access is via
                  * hypercalls.  Keep the address in the pte for reference.
                  */
                 pte = pfn_pte(PFN_DOWN(__pa(dummy_mapping)), PAGE_KERNEL);
                 break;
 #endif
 
         case FIX_PARAVIRT_BOOTMAP:
                 /* This is an MFN, but it isn't an IO mapping from the
                    IO domain */
                 pte = mfn_pte(phys, prot);
                 break;
 
         default:
                 /* By default, set_fixmap is used for hardware mappings */
                 pte = mfn_pte(phys, prot);
                 break;
         }
 
         vaddr = __fix_to_virt(idx);
         if (HYPERVISOR_update_va_mapping(vaddr, pte, UVMF_INVLPG))
                 BUG();
 
 #ifdef CONFIG_X86_VSYSCALL_EMULATION
         /* Replicate changes to map the vsyscall page into the user
            pagetable vsyscall mapping. */
         if (idx == VSYSCALL_PAGE)
                 set_pte_vaddr_pud(level3_user_vsyscall, vaddr, pte);
 #endif
 }
 
 static void xen_enter_lazy_mmu(void)
 {
         enter_lazy(XEN_LAZY_MMU);
 }
 
 static void xen_flush_lazy_mmu(void)
 {
         preempt_disable();
 
         if (xen_get_lazy_mode() == XEN_LAZY_MMU) {
                 arch_leave_lazy_mmu_mode();
                 arch_enter_lazy_mmu_mode();
         }
 
         preempt_enable();
 }
 
 static void __init xen_post_allocator_init(void)
 {
         pv_ops.mmu.set_pte = xen_set_pte;
         pv_ops.mmu.set_pmd = xen_set_pmd;
         pv_ops.mmu.set_pud = xen_set_pud;
         pv_ops.mmu.set_p4d = xen_set_p4d;
 
         /* This will work as long as patching hasn't happened yet
            (which it hasn't) */
         pv_ops.mmu.alloc_pte = xen_alloc_pte;
         pv_ops.mmu.alloc_pmd = xen_alloc_pmd;
         pv_ops.mmu.release_pte = xen_release_pte;
         pv_ops.mmu.release_pmd = xen_release_pmd;
         pv_ops.mmu.alloc_pud = xen_alloc_pud;
         pv_ops.mmu.release_pud = xen_release_pud;
         pv_ops.mmu.make_pte = PV_CALLEE_SAVE(xen_make_pte);
 
         pv_ops.mmu.write_cr3 = &xen_write_cr3;
 }
 
 static void xen_leave_lazy_mmu(void)
 {
         preempt_disable();
         xen_mc_flush();
         leave_lazy(XEN_LAZY_MMU);
         preempt_enable();
 }
 
 static const typeof(pv_ops) xen_mmu_ops __initconst = {
         .mmu = {
                 .read_cr2 = __PV_IS_CALLEE_SAVE(xen_read_cr2),
                 .write_cr2 = xen_write_cr2,
 
                 .read_cr3 = xen_read_cr3,
                 .write_cr3 = xen_write_cr3_init,
 
                 .flush_tlb_user = xen_flush_tlb,
                 .flush_tlb_kernel = xen_flush_tlb,
                 .flush_tlb_one_user = xen_flush_tlb_one_user,
                 .flush_tlb_multi = xen_flush_tlb_multi,
                 .tlb_remove_table = tlb_remove_table,
 
                 .pgd_alloc = xen_pgd_alloc,
                 .pgd_free = xen_pgd_free,
 
                 .alloc_pte = xen_alloc_pte_init,
                 .release_pte = xen_release_pte_init,
                 .alloc_pmd = xen_alloc_pmd_init,
                 .release_pmd = xen_release_pmd_init,
 
                 .set_pte = xen_set_pte_init,
                 .set_pmd = xen_set_pmd_hyper,
 
                 .ptep_modify_prot_start = xen_ptep_modify_prot_start,
                 .ptep_modify_prot_commit = xen_ptep_modify_prot_commit,
 
                 .pte_val = PV_CALLEE_SAVE(xen_pte_val),
                 .pgd_val = PV_CALLEE_SAVE(xen_pgd_val),
 
                 .make_pte = PV_CALLEE_SAVE(xen_make_pte_init),
                 .make_pgd = PV_CALLEE_SAVE(xen_make_pgd),
 
                 .set_pud = xen_set_pud_hyper,
 
                 .make_pmd = PV_CALLEE_SAVE(xen_make_pmd),
                 .pmd_val = PV_CALLEE_SAVE(xen_pmd_val),
 
                 .pud_val = PV_CALLEE_SAVE(xen_pud_val),
                 .make_pud = PV_CALLEE_SAVE(xen_make_pud),
                 .set_p4d = xen_set_p4d_hyper,
 
                 .alloc_pud = xen_alloc_pmd_init,
                 .release_pud = xen_release_pmd_init,
 
 #if CONFIG_PGTABLE_LEVELS >= 5
                 .p4d_val = PV_CALLEE_SAVE(xen_p4d_val),
                 .make_p4d = PV_CALLEE_SAVE(xen_make_p4d),
 #endif
 
                 .enter_mmap = xen_enter_mmap,
                 .exit_mmap = xen_exit_mmap,
 
                 .lazy_mode = {
                         .enter = xen_enter_lazy_mmu,
                         .leave = xen_leave_lazy_mmu,
                         .flush = xen_flush_lazy_mmu,
                 },
 
                 .set_fixmap = xen_set_fixmap,
         },
 };
 
 void __init xen_init_mmu_ops(void)
 {
         x86_init.paging.pagetable_init = xen_pagetable_init;
         x86_init.hyper.init_after_bootmem = xen_after_bootmem;
 
         pv_ops.mmu = xen_mmu_ops.mmu;
 
         memset(dummy_mapping, 0xff, PAGE_SIZE);
 }
 
 /* Protected by xen_reservation_lock. */
 #define MAX_CONTIG_ORDER 9 /* 2MB */
 static unsigned long discontig_frames[1<<MAX_CONTIG_ORDER];
 
 #define VOID_PTE (mfn_pte(0, __pgprot(0)))
 static void xen_zap_pfn_range(unsigned long vaddr, unsigned int order,
                                 unsigned long *in_frames,
                                 unsigned long *out_frames)
 {
         int i;
         struct multicall_space mcs;
 
         xen_mc_batch();
         for (i = 0; i < (1UL<<order); i++, vaddr += PAGE_SIZE) {
                 mcs = __xen_mc_entry(0);
 
                 if (in_frames)
                         in_frames[i] = virt_to_mfn((void *)vaddr);
 
                 MULTI_update_va_mapping(mcs.mc, vaddr, VOID_PTE, 0);
                 __set_phys_to_machine(virt_to_pfn((void *)vaddr), INVALID_P2M_ENTRY);
 
                 if (out_frames)
                         out_frames[i] = virt_to_pfn((void *)vaddr);
         }
         xen_mc_issue(0);
 }
 
 /*
  * Update the pfn-to-mfn mappings for a virtual address range, either to
  * point to an array of mfns, or contiguously from a single starting
  * mfn.
  */
 static void xen_remap_exchanged_ptes(unsigned long vaddr, int order,
                                      unsigned long *mfns,
                                      unsigned long first_mfn)
 {
         unsigned i, limit;
         unsigned long mfn;
 
         xen_mc_batch();
 
         limit = 1u << order;
         for (i = 0; i < limit; i++, vaddr += PAGE_SIZE) {
                 struct multicall_space mcs;
                 unsigned flags;
 
                 mcs = __xen_mc_entry(0);
                 if (mfns)
                         mfn = mfns[i];
                 else
                         mfn = first_mfn + i;
 
                 if (i < (limit - 1))
                         flags = 0;
                 else {
                         if (order == 0)
                                 flags = UVMF_INVLPG | UVMF_ALL;
                         else
                                 flags = UVMF_TLB_FLUSH | UVMF_ALL;
                 }
 
                 MULTI_update_va_mapping(mcs.mc, vaddr,
                                 mfn_pte(mfn, PAGE_KERNEL), flags);
 
                 set_phys_to_machine(virt_to_pfn((void *)vaddr), mfn);
         }
 
         xen_mc_issue(0);
 }
 
 /*
  * Perform the hypercall to exchange a region of our pfns to point to
  * memory with the required contiguous alignment.  Takes the pfns as
  * input, and populates mfns as output.
  *
  * Returns a success code indicating whether the hypervisor was able to
  * satisfy the request or not.
  */
 static int xen_exchange_memory(unsigned long extents_in, unsigned int order_in,
                                unsigned long *pfns_in,
                                unsigned long extents_out,
                                unsigned int order_out,
                                unsigned long *mfns_out,
                                unsigned int address_bits)
 {
         long rc;
         int success;
 
         struct xen_memory_exchange exchange = {
                 .in = {
                         .nr_extents   = extents_in,
                         .extent_order = order_in,
                         .extent_start = pfns_in,
                         .domid        = DOMID_SELF
                 },
                 .out = {
                         .nr_extents   = extents_out,
                         .extent_order = order_out,
                         .extent_start = mfns_out,
                         .address_bits = address_bits,
                         .domid        = DOMID_SELF
                 }
         };
 
         BUG_ON(extents_in << order_in != extents_out << order_out);
 
         rc = HYPERVISOR_memory_op(XENMEM_exchange, &exchange);
         success = (exchange.nr_exchanged == extents_in);
 
         BUG_ON(!success && ((exchange.nr_exchanged != 0) || (rc == 0)));
         BUG_ON(success && (rc != 0));
 
         return success;
 }
 
 int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
                                  unsigned int address_bits,
                                  dma_addr_t *dma_handle)
 {
         unsigned long *in_frames = discontig_frames, out_frame;
         unsigned long  flags;
         int            success;
         unsigned long vstart = (unsigned long)phys_to_virt(pstart);
 
         if (unlikely(order > MAX_CONTIG_ORDER))
                 return -ENOMEM;
 
         memset((void *) vstart, 0, PAGE_SIZE << order);
 
         spin_lock_irqsave(&xen_reservation_lock, flags);
 
         /* 1. Zap current PTEs, remembering MFNs. */
         xen_zap_pfn_range(vstart, order, in_frames, NULL);
 
         /* 2. Get a new contiguous memory extent. */
         out_frame = virt_to_pfn((void *)vstart);
         success = xen_exchange_memory(1UL << order, 0, in_frames,
                                       1, order, &out_frame,
                                       address_bits);
 
         /* 3. Map the new extent in place of old pages. */
         if (success)
                 xen_remap_exchanged_ptes(vstart, order, NULL, out_frame);
         else
                 xen_remap_exchanged_ptes(vstart, order, in_frames, 0);
 
         spin_unlock_irqrestore(&xen_reservation_lock, flags);
 
         *dma_handle = virt_to_machine(vstart).maddr;
         return success ? 0 : -ENOMEM;
 }
 
 void xen_destroy_contiguous_region(phys_addr_t pstart, unsigned int order)
 {
         unsigned long *out_frames = discontig_frames, in_frame;
         unsigned long  flags;
         int success;
         unsigned long vstart;
 
         if (unlikely(order > MAX_CONTIG_ORDER))
                 return;
 
         vstart = (unsigned long)phys_to_virt(pstart);
         memset((void *) vstart, 0, PAGE_SIZE << order);
 
         spin_lock_irqsave(&xen_reservation_lock, flags);
 
         /* 1. Find start MFN of contiguous extent. */
         in_frame = virt_to_mfn((void *)vstart);
 
         /* 2. Zap current PTEs. */
         xen_zap_pfn_range(vstart, order, NULL, out_frames);
 
         /* 3. Do the exchange for non-contiguous MFNs. */
         success = xen_exchange_memory(1, order, &in_frame, 1UL << order,
                                         0, out_frames, 0);
 
         /* 4. Map new pages in place of old pages. */
         if (success)
                 xen_remap_exchanged_ptes(vstart, order, out_frames, 0);
         else
                 xen_remap_exchanged_ptes(vstart, order, NULL, in_frame);
 
         spin_unlock_irqrestore(&xen_reservation_lock, flags);
 }
 
 static noinline void xen_flush_tlb_all(void)
 {
         struct mmuext_op *op;
         struct multicall_space mcs;
 
         preempt_disable();
 
         mcs = xen_mc_entry(sizeof(*op));
 
         op = mcs.args;
         op->cmd = MMUEXT_TLB_FLUSH_ALL;
         MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
 
         xen_mc_issue(XEN_LAZY_MMU);
 
         preempt_enable();
 }
 
 #define REMAP_BATCH_SIZE 16
 
 struct remap_data {
         xen_pfn_t *pfn;
         bool contiguous;
         bool no_translate;
         pgprot_t prot;
         struct mmu_update *mmu_update;
 };
 
 static int remap_area_pfn_pte_fn(pte_t *ptep, unsigned long addr, void *data)
 {
         struct remap_data *rmd = data;
         pte_t pte = pte_mkspecial(mfn_pte(*rmd->pfn, rmd->prot));
 
         /*
          * If we have a contiguous range, just update the pfn itself,
          * else update pointer to be "next pfn".
          */
         if (rmd->contiguous)
                 (*rmd->pfn)++;
         else
                 rmd->pfn++;
 
         rmd->mmu_update->ptr = virt_to_machine(ptep).maddr;
         rmd->mmu_update->ptr |= rmd->no_translate ?
                 MMU_PT_UPDATE_NO_TRANSLATE :
                 MMU_NORMAL_PT_UPDATE;
         rmd->mmu_update->val = pte_val_ma(pte);
         rmd->mmu_update++;
 
         return 0;
 }
 
 int xen_remap_pfn(struct vm_area_struct *vma, unsigned long addr,
                   xen_pfn_t *pfn, int nr, int *err_ptr, pgprot_t prot,
                   unsigned int domid, bool no_translate)
 {
         int err = 0;
         struct remap_data rmd;
         struct mmu_update mmu_update[REMAP_BATCH_SIZE];
         unsigned long range;
         int mapped = 0;
 
         BUG_ON(!((vma->vm_flags & (VM_PFNMAP | VM_IO)) == (VM_PFNMAP | VM_IO)));
 
         rmd.pfn = pfn;
         rmd.prot = prot;
         /*
          * We use the err_ptr to indicate if there we are doing a contiguous
          * mapping or a discontiguous mapping.
          */
         rmd.contiguous = !err_ptr;
         rmd.no_translate = no_translate;
 
         while (nr) {
                 int index = 0;
                 int done = 0;
                 int batch = min(REMAP_BATCH_SIZE, nr);
                 int batch_left = batch;
 
                 range = (unsigned long)batch << PAGE_SHIFT;
 
                 rmd.mmu_update = mmu_update;
                 err = apply_to_page_range(vma->vm_mm, addr, range,
                                           remap_area_pfn_pte_fn, &rmd);
                 if (err)
                         goto out;
 
                 /*
                  * We record the error for each page that gives an error, but
                  * continue mapping until the whole set is done
                  */
                 do {
                         int i;
 
                         err = HYPERVISOR_mmu_update(&mmu_update[index],
                                                     batch_left, &done, domid);
 
                         /*
                          * @err_ptr may be the same buffer as @gfn, so
                          * only clear it after each chunk of @gfn is
                          * used.
                          */
                         if (err_ptr) {
                                 for (i = index; i < index + done; i++)
                                         err_ptr[i] = 0;
                         }
                         if (err < 0) {
                                 if (!err_ptr)
                                         goto out;
                                 err_ptr[i] = err;
                                 done++; /* Skip failed frame. */
                         } else
                                 mapped += done;
                         batch_left -= done;
                         index += done;
                 } while (batch_left);
 
                 nr -= batch;
                 addr += range;
                 if (err_ptr)
                         err_ptr += batch;
                 cond_resched();
         }
 out:
 
         xen_flush_tlb_all();
 
         return err < 0 ? err : mapped;
 }
 EXPORT_SYMBOL_GPL(xen_remap_pfn);
 
 #ifdef CONFIG_VMCORE_INFO
 phys_addr_t paddr_vmcoreinfo_note(void)
 {
         if (xen_pv_domain())
                 return virt_to_machine(vmcoreinfo_note).maddr;
         else
                 return __pa(vmcoreinfo_note);
 }
 #endif /* CONFIG_KEXEC_CORE */
 

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