1 // SPDX-License-Identifier: GPL-2.0 1 // SPDX-License-Identifier: GPL-2.0
2 /* 2 /*
3 * mm/pgtable-generic.c 3 * mm/pgtable-generic.c
4 * 4 *
5 * Generic pgtable methods declared in linux/ 5 * Generic pgtable methods declared in linux/pgtable.h
6 * 6 *
7 * Copyright (C) 2010 Linus Torvalds 7 * Copyright (C) 2010 Linus Torvalds
8 */ 8 */
9 9
10 #include <linux/pagemap.h> 10 #include <linux/pagemap.h>
11 #include <linux/hugetlb.h> 11 #include <linux/hugetlb.h>
12 #include <linux/pgtable.h> 12 #include <linux/pgtable.h>
13 #include <linux/swap.h> 13 #include <linux/swap.h>
14 #include <linux/swapops.h> 14 #include <linux/swapops.h>
15 #include <linux/mm_inline.h> 15 #include <linux/mm_inline.h>
16 #include <asm/pgalloc.h> 16 #include <asm/pgalloc.h>
17 #include <asm/tlb.h> 17 #include <asm/tlb.h>
18 18
19 /* 19 /*
20 * If a p?d_bad entry is found while walking p 20 * If a p?d_bad entry is found while walking page tables, report
21 * the error, before resetting entry to p?d_no 21 * the error, before resetting entry to p?d_none. Usually (but
22 * very seldom) called out from the p?d_none_o 22 * very seldom) called out from the p?d_none_or_clear_bad macros.
23 */ 23 */
24 24
25 void pgd_clear_bad(pgd_t *pgd) 25 void pgd_clear_bad(pgd_t *pgd)
26 { 26 {
27 pgd_ERROR(*pgd); 27 pgd_ERROR(*pgd);
28 pgd_clear(pgd); 28 pgd_clear(pgd);
29 } 29 }
30 30
31 #ifndef __PAGETABLE_P4D_FOLDED 31 #ifndef __PAGETABLE_P4D_FOLDED
32 void p4d_clear_bad(p4d_t *p4d) 32 void p4d_clear_bad(p4d_t *p4d)
33 { 33 {
34 p4d_ERROR(*p4d); 34 p4d_ERROR(*p4d);
35 p4d_clear(p4d); 35 p4d_clear(p4d);
36 } 36 }
37 #endif 37 #endif
38 38
39 #ifndef __PAGETABLE_PUD_FOLDED 39 #ifndef __PAGETABLE_PUD_FOLDED
40 void pud_clear_bad(pud_t *pud) 40 void pud_clear_bad(pud_t *pud)
41 { 41 {
42 pud_ERROR(*pud); 42 pud_ERROR(*pud);
43 pud_clear(pud); 43 pud_clear(pud);
44 } 44 }
45 #endif 45 #endif
46 46
47 /* 47 /*
48 * Note that the pmd variant below can't be st 48 * Note that the pmd variant below can't be stub'ed out just as for p4d/pud
49 * above. pmd folding is special and typically 49 * above. pmd folding is special and typically pmd_* macros refer to upper
50 * level even when folded 50 * level even when folded
51 */ 51 */
52 void pmd_clear_bad(pmd_t *pmd) 52 void pmd_clear_bad(pmd_t *pmd)
53 { 53 {
54 pmd_ERROR(*pmd); 54 pmd_ERROR(*pmd);
55 pmd_clear(pmd); 55 pmd_clear(pmd);
56 } 56 }
57 57
58 #ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS 58 #ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
59 /* 59 /*
60 * Only sets the access flags (dirty, accessed 60 * Only sets the access flags (dirty, accessed), as well as write
61 * permission. Furthermore, we know it always 61 * permission. Furthermore, we know it always gets set to a "more
62 * permissive" setting, which allows most arch 62 * permissive" setting, which allows most architectures to optimize
63 * this. We return whether the PTE actually ch 63 * this. We return whether the PTE actually changed, which in turn
64 * instructs the caller to do things like upda 64 * instructs the caller to do things like update__mmu_cache. This
65 * used to be done in the caller, but sparc ne 65 * used to be done in the caller, but sparc needs minor faults to
66 * force that call on sun4c so we changed this 66 * force that call on sun4c so we changed this macro slightly
67 */ 67 */
68 int ptep_set_access_flags(struct vm_area_struc 68 int ptep_set_access_flags(struct vm_area_struct *vma,
69 unsigned long addres 69 unsigned long address, pte_t *ptep,
70 pte_t entry, int dir 70 pte_t entry, int dirty)
71 { 71 {
72 int changed = !pte_same(ptep_get(ptep) 72 int changed = !pte_same(ptep_get(ptep), entry);
73 if (changed) { 73 if (changed) {
74 set_pte_at(vma->vm_mm, address 74 set_pte_at(vma->vm_mm, address, ptep, entry);
75 flush_tlb_fix_spurious_fault(v 75 flush_tlb_fix_spurious_fault(vma, address, ptep);
76 } 76 }
77 return changed; 77 return changed;
78 } 78 }
79 #endif 79 #endif
80 80
81 #ifndef __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH 81 #ifndef __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
82 int ptep_clear_flush_young(struct vm_area_stru 82 int ptep_clear_flush_young(struct vm_area_struct *vma,
83 unsigned long addre 83 unsigned long address, pte_t *ptep)
84 { 84 {
85 int young; 85 int young;
86 young = ptep_test_and_clear_young(vma, 86 young = ptep_test_and_clear_young(vma, address, ptep);
87 if (young) 87 if (young)
88 flush_tlb_page(vma, address); 88 flush_tlb_page(vma, address);
89 return young; 89 return young;
90 } 90 }
91 #endif 91 #endif
92 92
93 #ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH 93 #ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH
94 pte_t ptep_clear_flush(struct vm_area_struct * 94 pte_t ptep_clear_flush(struct vm_area_struct *vma, unsigned long address,
95 pte_t *ptep) 95 pte_t *ptep)
96 { 96 {
97 struct mm_struct *mm = (vma)->vm_mm; 97 struct mm_struct *mm = (vma)->vm_mm;
98 pte_t pte; 98 pte_t pte;
99 pte = ptep_get_and_clear(mm, address, 99 pte = ptep_get_and_clear(mm, address, ptep);
100 if (pte_accessible(mm, pte)) 100 if (pte_accessible(mm, pte))
101 flush_tlb_page(vma, address); 101 flush_tlb_page(vma, address);
102 return pte; 102 return pte;
103 } 103 }
104 #endif 104 #endif
105 105
106 #ifdef CONFIG_TRANSPARENT_HUGEPAGE 106 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
107 107
108 #ifndef __HAVE_ARCH_PMDP_SET_ACCESS_FLAGS 108 #ifndef __HAVE_ARCH_PMDP_SET_ACCESS_FLAGS
109 int pmdp_set_access_flags(struct vm_area_struc 109 int pmdp_set_access_flags(struct vm_area_struct *vma,
110 unsigned long addres 110 unsigned long address, pmd_t *pmdp,
111 pmd_t entry, int dir 111 pmd_t entry, int dirty)
112 { 112 {
113 int changed = !pmd_same(*pmdp, entry); 113 int changed = !pmd_same(*pmdp, entry);
114 VM_BUG_ON(address & ~HPAGE_PMD_MASK); 114 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
115 if (changed) { 115 if (changed) {
116 set_pmd_at(vma->vm_mm, address 116 set_pmd_at(vma->vm_mm, address, pmdp, entry);
117 flush_pmd_tlb_range(vma, addre 117 flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
118 } 118 }
119 return changed; 119 return changed;
120 } 120 }
121 #endif 121 #endif
122 122
123 #ifndef __HAVE_ARCH_PMDP_CLEAR_YOUNG_FLUSH 123 #ifndef __HAVE_ARCH_PMDP_CLEAR_YOUNG_FLUSH
124 int pmdp_clear_flush_young(struct vm_area_stru 124 int pmdp_clear_flush_young(struct vm_area_struct *vma,
125 unsigned long addre 125 unsigned long address, pmd_t *pmdp)
126 { 126 {
127 int young; 127 int young;
128 VM_BUG_ON(address & ~HPAGE_PMD_MASK); 128 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
129 young = pmdp_test_and_clear_young(vma, 129 young = pmdp_test_and_clear_young(vma, address, pmdp);
130 if (young) 130 if (young)
131 flush_pmd_tlb_range(vma, addre 131 flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
132 return young; 132 return young;
133 } 133 }
134 #endif 134 #endif
135 135
136 #ifndef __HAVE_ARCH_PMDP_HUGE_CLEAR_FLUSH 136 #ifndef __HAVE_ARCH_PMDP_HUGE_CLEAR_FLUSH
137 pmd_t pmdp_huge_clear_flush(struct vm_area_str 137 pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
138 pmd_t *pmdp) 138 pmd_t *pmdp)
139 { 139 {
140 pmd_t pmd; 140 pmd_t pmd;
141 VM_BUG_ON(address & ~HPAGE_PMD_MASK); 141 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
142 VM_BUG_ON(pmd_present(*pmdp) && !pmd_t 142 VM_BUG_ON(pmd_present(*pmdp) && !pmd_trans_huge(*pmdp) &&
143 !pmd_devmap(*pmdp)) 143 !pmd_devmap(*pmdp));
144 pmd = pmdp_huge_get_and_clear(vma->vm_ 144 pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
145 flush_pmd_tlb_range(vma, address, addr 145 flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
146 return pmd; 146 return pmd;
147 } 147 }
148 148
149 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_P 149 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
150 pud_t pudp_huge_clear_flush(struct vm_area_str 150 pud_t pudp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
151 pud_t *pudp) 151 pud_t *pudp)
152 { 152 {
153 pud_t pud; 153 pud_t pud;
154 154
155 VM_BUG_ON(address & ~HPAGE_PUD_MASK); 155 VM_BUG_ON(address & ~HPAGE_PUD_MASK);
156 VM_BUG_ON(!pud_trans_huge(*pudp) && !p 156 VM_BUG_ON(!pud_trans_huge(*pudp) && !pud_devmap(*pudp));
157 pud = pudp_huge_get_and_clear(vma->vm_ 157 pud = pudp_huge_get_and_clear(vma->vm_mm, address, pudp);
158 flush_pud_tlb_range(vma, address, addr 158 flush_pud_tlb_range(vma, address, address + HPAGE_PUD_SIZE);
159 return pud; 159 return pud;
160 } 160 }
161 #endif 161 #endif
162 #endif 162 #endif
163 163
164 #ifndef __HAVE_ARCH_PGTABLE_DEPOSIT 164 #ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
165 void pgtable_trans_huge_deposit(struct mm_stru 165 void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
166 pgtable_t pgta 166 pgtable_t pgtable)
167 { 167 {
168 assert_spin_locked(pmd_lockptr(mm, pmd 168 assert_spin_locked(pmd_lockptr(mm, pmdp));
169 169
170 /* FIFO */ 170 /* FIFO */
171 if (!pmd_huge_pte(mm, pmdp)) 171 if (!pmd_huge_pte(mm, pmdp))
172 INIT_LIST_HEAD(&pgtable->lru); 172 INIT_LIST_HEAD(&pgtable->lru);
173 else 173 else
174 list_add(&pgtable->lru, &pmd_h 174 list_add(&pgtable->lru, &pmd_huge_pte(mm, pmdp)->lru);
175 pmd_huge_pte(mm, pmdp) = pgtable; 175 pmd_huge_pte(mm, pmdp) = pgtable;
176 } 176 }
177 #endif 177 #endif
178 178
179 #ifndef __HAVE_ARCH_PGTABLE_WITHDRAW 179 #ifndef __HAVE_ARCH_PGTABLE_WITHDRAW
180 /* no "address" argument so destroys page colo 180 /* no "address" argument so destroys page coloring of some arch */
181 pgtable_t pgtable_trans_huge_withdraw(struct m 181 pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp)
182 { 182 {
183 pgtable_t pgtable; 183 pgtable_t pgtable;
184 184
185 assert_spin_locked(pmd_lockptr(mm, pmd 185 assert_spin_locked(pmd_lockptr(mm, pmdp));
186 186
187 /* FIFO */ 187 /* FIFO */
188 pgtable = pmd_huge_pte(mm, pmdp); 188 pgtable = pmd_huge_pte(mm, pmdp);
189 pmd_huge_pte(mm, pmdp) = list_first_en 189 pmd_huge_pte(mm, pmdp) = list_first_entry_or_null(&pgtable->lru,
190 190 struct page, lru);
191 if (pmd_huge_pte(mm, pmdp)) 191 if (pmd_huge_pte(mm, pmdp))
192 list_del(&pgtable->lru); 192 list_del(&pgtable->lru);
193 return pgtable; 193 return pgtable;
194 } 194 }
195 #endif 195 #endif
196 196
197 #ifndef __HAVE_ARCH_PMDP_INVALIDATE 197 #ifndef __HAVE_ARCH_PMDP_INVALIDATE
198 pmd_t pmdp_invalidate(struct vm_area_struct *v 198 pmd_t pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
199 pmd_t *pmdp) 199 pmd_t *pmdp)
200 { 200 {
201 VM_WARN_ON_ONCE(!pmd_present(*pmdp)); 201 VM_WARN_ON_ONCE(!pmd_present(*pmdp));
202 pmd_t old = pmdp_establish(vma, addres 202 pmd_t old = pmdp_establish(vma, address, pmdp, pmd_mkinvalid(*pmdp));
203 flush_pmd_tlb_range(vma, address, addr 203 flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
204 return old; 204 return old;
205 } 205 }
206 #endif 206 #endif
207 207
208 #ifndef __HAVE_ARCH_PMDP_INVALIDATE_AD 208 #ifndef __HAVE_ARCH_PMDP_INVALIDATE_AD
209 pmd_t pmdp_invalidate_ad(struct vm_area_struct 209 pmd_t pmdp_invalidate_ad(struct vm_area_struct *vma, unsigned long address,
210 pmd_t *pmdp) 210 pmd_t *pmdp)
211 { 211 {
212 VM_WARN_ON_ONCE(!pmd_present(*pmdp)); 212 VM_WARN_ON_ONCE(!pmd_present(*pmdp));
213 return pmdp_invalidate(vma, address, p 213 return pmdp_invalidate(vma, address, pmdp);
214 } 214 }
215 #endif 215 #endif
216 216
217 #ifndef pmdp_collapse_flush 217 #ifndef pmdp_collapse_flush
218 pmd_t pmdp_collapse_flush(struct vm_area_struc 218 pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
219 pmd_t *pmdp) 219 pmd_t *pmdp)
220 { 220 {
221 /* 221 /*
222 * pmd and hugepage pte format are sam 222 * pmd and hugepage pte format are same. So we could
223 * use the same function. 223 * use the same function.
224 */ 224 */
225 pmd_t pmd; 225 pmd_t pmd;
226 226
227 VM_BUG_ON(address & ~HPAGE_PMD_MASK); 227 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
228 VM_BUG_ON(pmd_trans_huge(*pmdp)); 228 VM_BUG_ON(pmd_trans_huge(*pmdp));
229 pmd = pmdp_huge_get_and_clear(vma->vm_ 229 pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
230 230
231 /* collapse entails shooting down ptes 231 /* collapse entails shooting down ptes not pmd */
232 flush_tlb_range(vma, address, address 232 flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
233 return pmd; 233 return pmd;
234 } 234 }
235 #endif 235 #endif
236 236
237 /* arch define pte_free_defer in asm/pgalloc.h 237 /* arch define pte_free_defer in asm/pgalloc.h for its own implementation */
238 #ifndef pte_free_defer 238 #ifndef pte_free_defer
239 static void pte_free_now(struct rcu_head *head 239 static void pte_free_now(struct rcu_head *head)
240 { 240 {
241 struct page *page; 241 struct page *page;
242 242
243 page = container_of(head, struct page, 243 page = container_of(head, struct page, rcu_head);
244 pte_free(NULL /* mm not passed and not 244 pte_free(NULL /* mm not passed and not used */, (pgtable_t)page);
245 } 245 }
246 246
247 void pte_free_defer(struct mm_struct *mm, pgta 247 void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable)
248 { 248 {
249 struct page *page; 249 struct page *page;
250 250
251 page = pgtable; 251 page = pgtable;
252 call_rcu(&page->rcu_head, pte_free_now 252 call_rcu(&page->rcu_head, pte_free_now);
253 } 253 }
254 #endif /* pte_free_defer */ 254 #endif /* pte_free_defer */
255 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ 255 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
256 256
257 #if defined(CONFIG_GUP_GET_PXX_LOW_HIGH) && \ 257 #if defined(CONFIG_GUP_GET_PXX_LOW_HIGH) && \
258 (defined(CONFIG_SMP) || defined(CONFIG 258 (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RCU))
259 /* 259 /*
260 * See the comment above ptep_get_lockless() i 260 * See the comment above ptep_get_lockless() in include/linux/pgtable.h:
261 * the barriers in pmdp_get_lockless() cannot 261 * the barriers in pmdp_get_lockless() cannot guarantee that the value in
262 * pmd_high actually belongs with the value in 262 * pmd_high actually belongs with the value in pmd_low; but holding interrupts
263 * off blocks the TLB flush between present up 263 * off blocks the TLB flush between present updates, which guarantees that a
264 * successful __pte_offset_map() points to a p 264 * successful __pte_offset_map() points to a page from matched halves.
265 */ 265 */
266 static unsigned long pmdp_get_lockless_start(v 266 static unsigned long pmdp_get_lockless_start(void)
267 { 267 {
268 unsigned long irqflags; 268 unsigned long irqflags;
269 269
270 local_irq_save(irqflags); 270 local_irq_save(irqflags);
271 return irqflags; 271 return irqflags;
272 } 272 }
273 static void pmdp_get_lockless_end(unsigned lon 273 static void pmdp_get_lockless_end(unsigned long irqflags)
274 { 274 {
275 local_irq_restore(irqflags); 275 local_irq_restore(irqflags);
276 } 276 }
277 #else 277 #else
278 static unsigned long pmdp_get_lockless_start(v 278 static unsigned long pmdp_get_lockless_start(void) { return 0; }
279 static void pmdp_get_lockless_end(unsigned lon 279 static void pmdp_get_lockless_end(unsigned long irqflags) { }
280 #endif 280 #endif
281 281
282 pte_t *__pte_offset_map(pmd_t *pmd, unsigned l 282 pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp)
283 { 283 {
284 unsigned long irqflags; 284 unsigned long irqflags;
285 pmd_t pmdval; 285 pmd_t pmdval;
286 286
287 rcu_read_lock(); 287 rcu_read_lock();
288 irqflags = pmdp_get_lockless_start(); 288 irqflags = pmdp_get_lockless_start();
289 pmdval = pmdp_get_lockless(pmd); 289 pmdval = pmdp_get_lockless(pmd);
290 pmdp_get_lockless_end(irqflags); 290 pmdp_get_lockless_end(irqflags);
291 291
292 if (pmdvalp) 292 if (pmdvalp)
293 *pmdvalp = pmdval; 293 *pmdvalp = pmdval;
294 if (unlikely(pmd_none(pmdval) || is_pm 294 if (unlikely(pmd_none(pmdval) || is_pmd_migration_entry(pmdval)))
295 goto nomap; 295 goto nomap;
296 if (unlikely(pmd_trans_huge(pmdval) || 296 if (unlikely(pmd_trans_huge(pmdval) || pmd_devmap(pmdval)))
297 goto nomap; 297 goto nomap;
298 if (unlikely(pmd_bad(pmdval))) { 298 if (unlikely(pmd_bad(pmdval))) {
299 pmd_clear_bad(pmd); 299 pmd_clear_bad(pmd);
300 goto nomap; 300 goto nomap;
301 } 301 }
302 return __pte_map(&pmdval, addr); 302 return __pte_map(&pmdval, addr);
303 nomap: 303 nomap:
304 rcu_read_unlock(); 304 rcu_read_unlock();
305 return NULL; 305 return NULL;
306 } 306 }
307 307
308 pte_t *pte_offset_map_nolock(struct mm_struct 308 pte_t *pte_offset_map_nolock(struct mm_struct *mm, pmd_t *pmd,
309 unsigned long add 309 unsigned long addr, spinlock_t **ptlp)
310 { 310 {
311 pmd_t pmdval; 311 pmd_t pmdval;
312 pte_t *pte; 312 pte_t *pte;
313 313
314 pte = __pte_offset_map(pmd, addr, &pmd 314 pte = __pte_offset_map(pmd, addr, &pmdval);
315 if (likely(pte)) 315 if (likely(pte))
316 *ptlp = pte_lockptr(mm, &pmdva 316 *ptlp = pte_lockptr(mm, &pmdval);
317 return pte; 317 return pte;
318 } 318 }
319 319
320 /* 320 /*
321 * pte_offset_map_lock(mm, pmd, addr, ptlp), a 321 * pte_offset_map_lock(mm, pmd, addr, ptlp), and its internal implementation
322 * __pte_offset_map_lock() below, is usually c 322 * __pte_offset_map_lock() below, is usually called with the pmd pointer for
323 * addr, reached by walking down the mm's pgd, 323 * addr, reached by walking down the mm's pgd, p4d, pud for addr: either while
324 * holding mmap_lock or vma lock for read or f 324 * holding mmap_lock or vma lock for read or for write; or in truncate or rmap
325 * context, while holding file's i_mmap_lock o 325 * context, while holding file's i_mmap_lock or anon_vma lock for read (or for
326 * write). In a few cases, it may be used with 326 * write). In a few cases, it may be used with pmd pointing to a pmd_t already
327 * copied to or constructed on the stack. 327 * copied to or constructed on the stack.
328 * 328 *
329 * When successful, it returns the pte pointer 329 * When successful, it returns the pte pointer for addr, with its page table
330 * kmapped if necessary (when CONFIG_HIGHPTE), 330 * kmapped if necessary (when CONFIG_HIGHPTE), and locked against concurrent
331 * modification by software, with a pointer to 331 * modification by software, with a pointer to that spinlock in ptlp (in some
332 * configs mm->page_table_lock, in SPLIT_PTLOC 332 * configs mm->page_table_lock, in SPLIT_PTLOCK configs a spinlock in table's
333 * struct page). pte_unmap_unlock(pte, ptl) t 333 * struct page). pte_unmap_unlock(pte, ptl) to unlock and unmap afterwards.
334 * 334 *
335 * But it is unsuccessful, returning NULL with 335 * But it is unsuccessful, returning NULL with *ptlp unchanged, if there is no
336 * page table at *pmd: if, for example, the pa 336 * page table at *pmd: if, for example, the page table has just been removed,
337 * or replaced by the huge pmd of a THP. (Whe 337 * or replaced by the huge pmd of a THP. (When successful, *pmd is rechecked
338 * after acquiring the ptlock, and retried int 338 * after acquiring the ptlock, and retried internally if it changed: so that a
339 * page table can be safely removed or replace 339 * page table can be safely removed or replaced by THP while holding its lock.)
340 * 340 *
341 * pte_offset_map(pmd, addr), and its internal 341 * pte_offset_map(pmd, addr), and its internal helper __pte_offset_map() above,
342 * just returns the pte pointer for addr, its 342 * just returns the pte pointer for addr, its page table kmapped if necessary;
343 * or NULL if there is no page table at *pmd. 343 * or NULL if there is no page table at *pmd. It does not attempt to lock the
344 * page table, so cannot normally be used when 344 * page table, so cannot normally be used when the page table is to be updated,
345 * or when entries read must be stable. But i 345 * or when entries read must be stable. But it does take rcu_read_lock(): so
346 * that even when page table is racily removed 346 * that even when page table is racily removed, it remains a valid though empty
347 * and disconnected table. Until pte_unmap(pt 347 * and disconnected table. Until pte_unmap(pte) unmaps and rcu_read_unlock()s
348 * afterwards. 348 * afterwards.
349 * 349 *
350 * pte_offset_map_nolock(mm, pmd, addr, ptlp), 350 * pte_offset_map_nolock(mm, pmd, addr, ptlp), above, is like pte_offset_map();
351 * but when successful, it also outputs a poin 351 * but when successful, it also outputs a pointer to the spinlock in ptlp - as
352 * pte_offset_map_lock() does, but in this cas 352 * pte_offset_map_lock() does, but in this case without locking it. This helps
353 * the caller to avoid a later pte_lockptr(mm, 353 * the caller to avoid a later pte_lockptr(mm, *pmd), which might by that time
354 * act on a changed *pmd: pte_offset_map_noloc 354 * act on a changed *pmd: pte_offset_map_nolock() provides the correct spinlock
355 * pointer for the page table that it returns. 355 * pointer for the page table that it returns. In principle, the caller should
356 * recheck *pmd once the lock is taken; in pra 356 * recheck *pmd once the lock is taken; in practice, no callsite needs that -
357 * either the mmap_lock for write, or pte_same 357 * either the mmap_lock for write, or pte_same() check on contents, is enough.
358 * 358 *
359 * Note that free_pgtables(), used after unmap 359 * Note that free_pgtables(), used after unmapping detached vmas, or when
360 * exiting the whole mm, does not take page ta 360 * exiting the whole mm, does not take page table lock before freeing a page
361 * table, and may not use RCU at all: "outside 361 * table, and may not use RCU at all: "outsiders" like khugepaged should avoid
362 * pte_offset_map() and co once the vma is det 362 * pte_offset_map() and co once the vma is detached from mm or mm_users is zero.
363 */ 363 */
364 pte_t *__pte_offset_map_lock(struct mm_struct 364 pte_t *__pte_offset_map_lock(struct mm_struct *mm, pmd_t *pmd,
365 unsigned long add 365 unsigned long addr, spinlock_t **ptlp)
366 { 366 {
367 spinlock_t *ptl; 367 spinlock_t *ptl;
368 pmd_t pmdval; 368 pmd_t pmdval;
369 pte_t *pte; 369 pte_t *pte;
370 again: 370 again:
371 pte = __pte_offset_map(pmd, addr, &pmd 371 pte = __pte_offset_map(pmd, addr, &pmdval);
372 if (unlikely(!pte)) 372 if (unlikely(!pte))
373 return pte; 373 return pte;
374 ptl = pte_lockptr(mm, &pmdval); 374 ptl = pte_lockptr(mm, &pmdval);
375 spin_lock(ptl); 375 spin_lock(ptl);
376 if (likely(pmd_same(pmdval, pmdp_get_l 376 if (likely(pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
377 *ptlp = ptl; 377 *ptlp = ptl;
378 return pte; 378 return pte;
379 } 379 }
380 pte_unmap_unlock(pte, ptl); 380 pte_unmap_unlock(pte, ptl);
381 goto again; 381 goto again;
382 } 382 }
383 383
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