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