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)
  17 {
  18         pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
  19         if (!(pvmw->flags & PVMW_SYNC)) {
  20                 if (pvmw->flags & PVMW_MIGRATION) {
  21                         if (!is_swap_pte(*pvmw->pte))
  22                                 return false;
  23                 } else {
  24                         /*
  25                          * We get here when we are trying to unmap a private
  26                          * device page from the process address space. Such
  27                          * page is not CPU accessible and thus is mapped as
  28                          * a special swap entry, nonetheless it still does
  29                          * count as a valid regular mapping for the page (and
  30                          * is accounted as such in page maps count).
  31                          *
  32                          * So handle this special case as if it was a normal
  33                          * page mapping ie lock CPU page table and returns
  34                          * true.
  35                          *
  36                          * For more details on device private memory see HMM
  37                          * (include/linux/hmm.h or mm/hmm.c).
  38                          */
  39                         if (is_swap_pte(*pvmw->pte)) {
  40                                 swp_entry_t entry;
  41
  42                                 /* Handle un-addressable ZONE_DEVICE memory */
  43                                 entry = pte_to_swp_entry(*pvmw->pte);
  44                                 if (!is_device_private_entry(entry))
  45                                         return false;
  46                         } else if (!pte_present(*pvmw->pte))
  47                                 return false;
  48                 }
  49         }
  50         pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
  51         spin_lock(pvmw->ptl);
  52         return true;
  53 }
  54
  55 static inline bool pfn_is_match(struct page *page, unsigned long pfn)
  56 {
  57         unsigned long page_pfn = page_to_pfn(page);
  58
  59         /* normal page and hugetlbfs page */
  60         if (!PageTransCompound(page) || PageHuge(page))
  61                 return page_pfn == pfn;
  62
  63         /* THP can be referenced by any subpage */
  64         return pfn >= page_pfn && pfn - page_pfn < thp_nr_pages(page);
  65 }
  66
  67 /**
  68  * check_pte - check if @pvmw->page is mapped at the @pvmw->pte
  69  * @pvmw: page_vma_mapped_walk struct, includes a pair pte and page for checking
  70  *
  71  * page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
  72  * mapped. check_pte() has to validate this.
  73  *
  74  * pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
  75  * arbitrary page.
  76  *
  77  * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
  78  * entry that points to @pvmw->page or any subpage in case of THP.
  79  *
  80  * If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
  81  * pvmw->page or any subpage in case of THP.
  82  *
  83  * Otherwise, return false.
  84  *
  85  */
  86 static bool check_pte(struct page_vma_mapped_walk *pvmw)
  87 {
  88         unsigned long pfn;
  89
  90         if (pvmw->flags & PVMW_MIGRATION) {
  91                 swp_entry_t entry;
  92                 if (!is_swap_pte(*pvmw->pte))
  93                         return false;
  94                 entry = pte_to_swp_entry(*pvmw->pte);
  95
  96                 if (!is_migration_entry(entry))
  97                         return false;
  98
  99                 pfn = migration_entry_to_pfn(entry);
 100         } else if (is_swap_pte(*pvmw->pte)) {
 101                 swp_entry_t entry;
 102
 103                 /* Handle un-addressable ZONE_DEVICE memory */
 104                 entry = pte_to_swp_entry(*pvmw->pte);
 105                 if (!is_device_private_entry(entry))
 106                         return false;
 107
 108                 pfn = device_private_entry_to_pfn(entry);
 109         } else {
 110                 if (!pte_present(*pvmw->pte))
 111                         return false;
 112
 113                 pfn = pte_pfn(*pvmw->pte);
 114         }
 115
 116         return pfn_is_match(pvmw->page, pfn);
 117 }
 118
 119 /**
 120  * page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
 121  * @pvmw->address
 122  * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
 123  * must be set. pmd, pte and ptl must be NULL.
 124  *
 125  * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
 126  * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
 127  * adjusted if needed (for PTE-mapped THPs).
 128  *
 129  * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
 130  * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
 131  * a loop to find all PTEs that map the THP.
 132  *
 133  * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
 134  * regardless of which page table level the page is mapped at. @pvmw->pmd is
 135  * NULL.
 136  *
 137  * Retruns false if there are no more page table entries for the page in
 138  * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
 139  *
 140  * If you need to stop the walk before page_vma_mapped_walk() returned false,
 141  * use page_vma_mapped_walk_done(). It will do the housekeeping.
 142  */
 143 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 144 {
 145         struct mm_struct *mm = pvmw->vma->vm_mm;
 146         struct page *page = pvmw->page;
 147         pgd_t *pgd;
 148         p4d_t *p4d;
 149         pud_t *pud;
 150         pmd_t pmde;
 151
 152         /* The only possible pmd mapping has been handled on last iteration */
 153         if (pvmw->pmd && !pvmw->pte)
 154                 return not_found(pvmw);
 155
 156         if (pvmw->pte)
 157                 goto next_pte;
 158
 159         if (unlikely(PageHuge(pvmw->page))) {
 160                 /* when pud is not present, pte will be NULL */
 161                 pvmw->pte = huge_pte_offset(mm, pvmw->address, page_size(page));
 162                 if (!pvmw->pte)
 163                         return false;
 164
 165                 pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
 166                 spin_lock(pvmw->ptl);
 167                 if (!check_pte(pvmw))
 168                         return not_found(pvmw);
 169                 return true;
 170         }
 171 restart:
 172         pgd = pgd_offset(mm, pvmw->address);
 173         if (!pgd_present(*pgd))
 174                 return false;
 175         p4d = p4d_offset(pgd, pvmw->address);
 176         if (!p4d_present(*p4d))
 177                 return false;
 178         pud = pud_offset(p4d, pvmw->address);
 179         if (!pud_present(*pud))
 180                 return false;
 181         pvmw->pmd = pmd_offset(pud, pvmw->address);
 182         /*
 183          * Make sure the pmd value isn't cached in a register by the
 184          * compiler and used as a stale value after we've observed a
 185          * subsequent update.
 186          */
 187         pmde = READ_ONCE(*pvmw->pmd);
 188         if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
 189                 pvmw->ptl = pmd_lock(mm, pvmw->pmd);
 190                 if (likely(pmd_trans_huge(*pvmw->pmd))) {
 191                         if (pvmw->flags & PVMW_MIGRATION)
 192                                 return not_found(pvmw);
 193                         if (pmd_page(*pvmw->pmd) != page)
 194                                 return not_found(pvmw);
 195                         return true;
 196                 } else if (!pmd_present(*pvmw->pmd)) {
 197                         if (thp_migration_supported()) {
 198                                 if (!(pvmw->flags & PVMW_MIGRATION))
 199                                         return not_found(pvmw);
 200                                 if (is_migration_entry(pmd_to_swp_entry(*pvmw->pmd))) {
 201                                         swp_entry_t entry = pmd_to_swp_entry(*pvmw->pmd);
 202
 203                                         if (migration_entry_to_page(entry) != page)
 204                                                 return not_found(pvmw);
 205                                         return true;
 206                                 }
 207                         }
 208                         return not_found(pvmw);
 209                 } else {
 210                         /* THP pmd was split under us: handle on pte level */
 211                         spin_unlock(pvmw->ptl);
 212                         pvmw->ptl = NULL;
 213                 }
 214         } else if (!pmd_present(pmde)) {
 215                 return false;
 216         }
 217         if (!map_pte(pvmw))
 218                 goto next_pte;
 219         while (1) {
 220                 if (check_pte(pvmw))
 221                         return true;
 222 next_pte:
 223                 /* Seek to next pte only makes sense for THP */
 224                 if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page))
 225                         return not_found(pvmw);
 226                 do {
 227                         pvmw->address += PAGE_SIZE;
 228                         if (pvmw->address >= pvmw->vma->vm_end ||
 229                             pvmw->address >=
 230                                         __vma_address(pvmw->page, pvmw->vma) +
 231                                         thp_size(pvmw->page))
 232                                 return not_found(pvmw);
 233                         /* Did we cross page table boundary? */
 234                         if (pvmw->address % PMD_SIZE == 0) {
 235                                 pte_unmap(pvmw->pte);
 236                                 if (pvmw->ptl) {
 237                                         spin_unlock(pvmw->ptl);
 238                                         pvmw->ptl = NULL;
 239                                 }
 240                                 goto restart;
 241                         } else {
 242                                 pvmw->pte++;
 243                         }
 244                 } while (pte_none(*pvmw->pte));
 245
 246                 if (!pvmw->ptl) {
 247                         pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
 248                         spin_lock(pvmw->ptl);
 249                 }
 250         }
 251 }
 252
 253 /**
 254  * page_mapped_in_vma - check whether a page is really mapped in a VMA
 255  * @page: the page to test
 256  * @vma: the VMA to test
 257  *
 258  * Returns 1 if the page is mapped into the page tables of the VMA, 0
 259  * if the page is not mapped into the page tables of this VMA.  Only
 260  * valid for normal file or anonymous VMAs.
 261  */
 262 int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
 263 {
 264         struct page_vma_mapped_walk pvmw = {
 265                 .page = page,
 266                 .vma = vma,
 267                 .flags = PVMW_SYNC,
 268         };
 269         unsigned long start, end;
 270
 271         start = __vma_address(page, vma);
 272         end = start + thp_size(page) - PAGE_SIZE;
 273
 274         if (unlikely(end < vma->vm_start || start >= vma->vm_end))
 275                 return 0;
 276         pvmw.address = max(start, vma->vm_start);
 277         if (!page_vma_mapped_walk(&pvmw))
 278                 return 0;
 279         page_vma_mapped_walk_done(&pvmw);
 280         return 1;
 281 }