mm/page_vma_mapped.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/mm.h>
   3 #include <linux/rmap.h>
   4 #include <linux/hugetlb.h>
   5 #include <linux/swap.h>
   6 #include <linux/swapops.h>
   7
   8 #include "internal.h"
   9
  10 static inline bool not_found(struct page_vma_mapped_walk *pvmw)
  11 {
  12         page_vma_mapped_walk_done(pvmw);
  13         return false;
  14 }
  15
  16 static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp)
  17 {
  18         pte_t ptent;
  19
  20         if (pvmw->flags & PVMW_SYNC) {
  21                 /* Use the stricter lookup */
  22                 pvmw->pte = pte_offset_map_lock(pvmw->vma->vm_mm, pvmw->pmd,
  23                                                 pvmw->address, &pvmw->ptl);
  24                 *ptlp = pvmw->ptl;
  25                 return !!pvmw->pte;
  26         }
  27
  28         /*
  29          * It is important to return the ptl corresponding to pte,
  30          * in case *pvmw->pmd changes underneath us; so we need to
  31          * return it even when choosing not to lock, in case caller
  32          * proceeds to loop over next ptes, and finds a match later.
  33          * Though, in most cases, page lock already protects this.
  34          */
  35         pvmw->pte = pte_offset_map_nolock(pvmw->vma->vm_mm, pvmw->pmd,
  36                                           pvmw->address, ptlp);
  37         if (!pvmw->pte)
  38                 return false;
  39
  40         ptent = ptep_get(pvmw->pte);
  41
  42         if (pvmw->flags & PVMW_MIGRATION) {
  43                 if (!is_swap_pte(ptent))
  44                         return false;
  45         } else if (is_swap_pte(ptent)) {
  46                 swp_entry_t entry;
  47                 /*
  48                  * Handle un-addressable ZONE_DEVICE memory.
  49                  *
  50                  * We get here when we are trying to unmap a private
  51                  * device page from the process address space. Such
  52                  * page is not CPU accessible and thus is mapped as
  53                  * a special swap entry, nonetheless it still does
  54                  * count as a valid regular mapping for the page
  55                  * (and is accounted as such in page maps count).
  56                  *
  57                  * So handle this special case as if it was a normal
  58                  * page mapping ie lock CPU page table and return true.
  59                  *
  60                  * For more details on device private memory see HMM
  61                  * (include/linux/hmm.h or mm/hmm.c).
  62                  */
  63                 entry = pte_to_swp_entry(ptent);
  64                 if (!is_device_private_entry(entry) &&
  65                     !is_device_exclusive_entry(entry))
  66                         return false;
  67         } else if (!pte_present(ptent)) {
  68                 return false;
  69         }
  70         pvmw->ptl = *ptlp;
  71         spin_lock(pvmw->ptl);
  72         return true;
  73 }
  74
  75 /**
  76  * check_pte - check if [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages) is
  77  * mapped at the @pvmw->pte
  78  * @pvmw: page_vma_mapped_walk struct, includes a pair pte and pfn range
  79  * for checking
  80  *
  81  * page_vma_mapped_walk() found a place where pfn range is *potentially*
  82  * mapped. check_pte() has to validate this.
  83  *
  84  * pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
  85  * arbitrary page.
  86  *
  87  * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
  88  * entry that points to [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages)
  89  *
  90  * If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
  91  * [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages)
  92  *
  93  * Otherwise, return false.
  94  *
  95  */
  96 static bool check_pte(struct page_vma_mapped_walk *pvmw)
  97 {
  98         unsigned long pfn;
  99         pte_t ptent = ptep_get(pvmw->pte);
 100
 101         if (pvmw->flags & PVMW_MIGRATION) {
 102                 swp_entry_t entry;
 103                 if (!is_swap_pte(ptent))
 104                         return false;
 105                 entry = pte_to_swp_entry(ptent);
 106
 107                 if (!is_migration_entry(entry) &&
 108                     !is_device_exclusive_entry(entry))
 109                         return false;
 110
 111                 pfn = swp_offset_pfn(entry);
 112         } else if (is_swap_pte(ptent)) {
 113                 swp_entry_t entry;
 114
 115                 /* Handle un-addressable ZONE_DEVICE memory */
 116                 entry = pte_to_swp_entry(ptent);
 117                 if (!is_device_private_entry(entry) &&
 118                     !is_device_exclusive_entry(entry))
 119                         return false;
 120
 121                 pfn = swp_offset_pfn(entry);
 122         } else {
 123                 if (!pte_present(ptent))
 124                         return false;
 125
 126                 pfn = pte_pfn(ptent);
 127         }
 128
 129         return (pfn - pvmw->pfn) < pvmw->nr_pages;
 130 }
 131
 132 /* Returns true if the two ranges overlap.  Careful to not overflow. */
 133 static bool check_pmd(unsigned long pfn, struct page_vma_mapped_walk *pvmw)
 134 {
 135         if ((pfn + HPAGE_PMD_NR - 1) < pvmw->pfn)
 136                 return false;
 137         if (pfn > pvmw->pfn + pvmw->nr_pages - 1)
 138                 return false;
 139         return true;
 140 }
 141
 142 static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
 143 {
 144         pvmw->address = (pvmw->address + size) & ~(size - 1);
 145         if (!pvmw->address)
 146                 pvmw->address = ULONG_MAX;
 147 }
 148
 149 /**
 150  * page_vma_mapped_walk - check if @pvmw->pfn is mapped in @pvmw->vma at
 151  * @pvmw->address
 152  * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
 153  * must be set. pmd, pte and ptl must be NULL.
 154  *
 155  * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
 156  * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
 157  * adjusted if needed (for PTE-mapped THPs).
 158  *
 159  * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
 160  * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
 161  * a loop to find all PTEs that map the THP.
 162  *
 163  * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
 164  * regardless of which page table level the page is mapped at. @pvmw->pmd is
 165  * NULL.
 166  *
 167  * Returns false if there are no more page table entries for the page in
 168  * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
 169  *
 170  * If you need to stop the walk before page_vma_mapped_walk() returned false,
 171  * use page_vma_mapped_walk_done(). It will do the housekeeping.
 172  */
 173 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 174 {
 175         struct vm_area_struct *vma = pvmw->vma;
 176         struct mm_struct *mm = vma->vm_mm;
 177         unsigned long end;
 178         spinlock_t *ptl;
 179         pgd_t *pgd;
 180         p4d_t *p4d;
 181         pud_t *pud;
 182         pmd_t pmde;
 183
 184         /* The only possible pmd mapping has been handled on last iteration */
 185         if (pvmw->pmd && !pvmw->pte)
 186                 return not_found(pvmw);
 187
 188         if (unlikely(is_vm_hugetlb_page(vma))) {
 189                 struct hstate *hstate = hstate_vma(vma);
 190                 unsigned long size = huge_page_size(hstate);
 191                 /* The only possible mapping was handled on last iteration */
 192                 if (pvmw->pte)
 193                         return not_found(pvmw);
 194                 /*
 195                  * All callers that get here will already hold the
 196                  * i_mmap_rwsem.  Therefore, no additional locks need to be
 197                  * taken before calling hugetlb_walk().
 198                  */
 199                 pvmw->pte = hugetlb_walk(vma, pvmw->address, size);
 200                 if (!pvmw->pte)
 201                         return false;
 202
 203                 pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte);
 204                 if (!check_pte(pvmw))
 205                         return not_found(pvmw);
 206                 return true;
 207         }
 208
 209         end = vma_address_end(pvmw);
 210         if (pvmw->pte)
 211                 goto next_pte;
 212 restart:
 213         do {
 214                 pgd = pgd_offset(mm, pvmw->address);
 215                 if (!pgd_present(*pgd)) {
 216                         step_forward(pvmw, PGDIR_SIZE);
 217                         continue;
 218                 }
 219                 p4d = p4d_offset(pgd, pvmw->address);
 220                 if (!p4d_present(*p4d)) {
 221                         step_forward(pvmw, P4D_SIZE);
 222                         continue;
 223                 }
 224                 pud = pud_offset(p4d, pvmw->address);
 225                 if (!pud_present(*pud)) {
 226                         step_forward(pvmw, PUD_SIZE);
 227                         continue;
 228                 }
 229
 230                 pvmw->pmd = pmd_offset(pud, pvmw->address);
 231                 /*
 232                  * Make sure the pmd value isn't cached in a register by the
 233                  * compiler and used as a stale value after we've observed a
 234                  * subsequent update.
 235                  */
 236                 pmde = pmdp_get_lockless(pvmw->pmd);
 237
 238                 if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde) ||
 239                     (pmd_present(pmde) && pmd_devmap(pmde))) {
 240                         pvmw->ptl = pmd_lock(mm, pvmw->pmd);
 241                         pmde = *pvmw->pmd;
 242                         if (!pmd_present(pmde)) {
 243                                 swp_entry_t entry;
 244
 245                                 if (!thp_migration_supported() ||
 246                                     !(pvmw->flags & PVMW_MIGRATION))
 247                                         return not_found(pvmw);
 248                                 entry = pmd_to_swp_entry(pmde);
 249                                 if (!is_migration_entry(entry) ||
 250                                     !check_pmd(swp_offset_pfn(entry), pvmw))
 251                                         return not_found(pvmw);
 252                                 return true;
 253                         }
 254                         if (likely(pmd_trans_huge(pmde) || pmd_devmap(pmde))) {
 255                                 if (pvmw->flags & PVMW_MIGRATION)
 256                                         return not_found(pvmw);
 257                                 if (!check_pmd(pmd_pfn(pmde), pvmw))
 258                                         return not_found(pvmw);
 259                                 return true;
 260                         }
 261                         /* THP pmd was split under us: handle on pte level */
 262                         spin_unlock(pvmw->ptl);
 263                         pvmw->ptl = NULL;
 264                 } else if (!pmd_present(pmde)) {
 265                         /*
 266                          * If PVMW_SYNC, take and drop THP pmd lock so that we
 267                          * cannot return prematurely, while zap_huge_pmd() has
 268                          * cleared *pmd but not decremented compound_mapcount().
 269                          */
 270                         if ((pvmw->flags & PVMW_SYNC) &&
 271                             transhuge_vma_suitable(vma, pvmw->address) &&
 272                             (pvmw->nr_pages >= HPAGE_PMD_NR)) {
 273                                 spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);
 274
 275                                 spin_unlock(ptl);
 276                         }
 277                         step_forward(pvmw, PMD_SIZE);
 278                         continue;
 279                 }
 280                 if (!map_pte(pvmw, &ptl)) {
 281                         if (!pvmw->pte)
 282                                 goto restart;
 283                         goto next_pte;
 284                 }
 285 this_pte:
 286                 if (check_pte(pvmw))
 287                         return true;
 288 next_pte:
 289                 do {
 290                         pvmw->address += PAGE_SIZE;
 291                         if (pvmw->address >= end)
 292                                 return not_found(pvmw);
 293                         /* Did we cross page table boundary? */
 294                         if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {
 295                                 if (pvmw->ptl) {
 296                                         spin_unlock(pvmw->ptl);
 297                                         pvmw->ptl = NULL;
 298                                 }
 299                                 pte_unmap(pvmw->pte);
 300                                 pvmw->pte = NULL;
 301                                 goto restart;
 302                         }
 303                         pvmw->pte++;
 304                 } while (pte_none(ptep_get(pvmw->pte)));
 305
 306                 if (!pvmw->ptl) {
 307                         pvmw->ptl = ptl;
 308                         spin_lock(pvmw->ptl);
 309                 }
 310                 goto this_pte;
 311         } while (pvmw->address < end);
 312
 313         return false;
 314 }
 315
 316 /**
 317  * page_mapped_in_vma - check whether a page is really mapped in a VMA
 318  * @page: the page to test
 319  * @vma: the VMA to test
 320  *
 321  * Returns 1 if the page is mapped into the page tables of the VMA, 0
 322  * if the page is not mapped into the page tables of this VMA.  Only
 323  * valid for normal file or anonymous VMAs.
 324  */
 325 int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
 326 {
 327         struct page_vma_mapped_walk pvmw = {
 328                 .pfn = page_to_pfn(page),
 329                 .nr_pages = 1,
 330                 .vma = vma,
 331                 .flags = PVMW_SYNC,
 332         };
 333
 334         pvmw.address = vma_address(page, vma);
 335         if (pvmw.address == -EFAULT)
 336                 return 0;
 337         if (!page_vma_mapped_walk(&pvmw))
 338                 return 0;
 339         page_vma_mapped_walk_done(&pvmw);
 340         return 1;
 341 }