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