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 /**
  56  * check_pte - check if @pvmw->page is mapped at the @pvmw->pte
  57  *
  58  * page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
  59  * mapped. check_pte() has to validate this.
  60  *
  61  * @pvmw->pte may point to empty PTE, swap PTE or PTE pointing to arbitrary
  62  * page.
  63  *
  64  * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
  65  * entry that points to @pvmw->page or any subpage in case of THP.
  66  *
  67  * If PVMW_MIGRATION flag is not set, returns true if @pvmw->pte points to
  68  * @pvmw->page or any subpage in case of THP.
  69  *
  70  * Otherwise, return false.
  71  *
  72  */
  73 static bool check_pte(struct page_vma_mapped_walk *pvmw)
  74 {
  75         unsigned long pfn;
  76
  77         if (pvmw->flags & PVMW_MIGRATION) {
  78                 swp_entry_t entry;
  79                 if (!is_swap_pte(*pvmw->pte))
  80                         return false;
  81                 entry = pte_to_swp_entry(*pvmw->pte);
  82
  83                 if (!is_migration_entry(entry))
  84                         return false;
  85
  86                 pfn = migration_entry_to_pfn(entry);
  87         } else if (is_swap_pte(*pvmw->pte)) {
  88                 swp_entry_t entry;
  89
  90                 /* Handle un-addressable ZONE_DEVICE memory */
  91                 entry = pte_to_swp_entry(*pvmw->pte);
  92                 if (!is_device_private_entry(entry))
  93                         return false;
  94
  95                 pfn = device_private_entry_to_pfn(entry);
  96         } else {
  97                 if (!pte_present(*pvmw->pte))
  98                         return false;
  99
 100                 pfn = pte_pfn(*pvmw->pte);
 101         }
 102
 103         if (pfn < page_to_pfn(pvmw->page))
 104                 return false;
 105
 106         /* THP can be referenced by any subpage */
 107         if (pfn - page_to_pfn(pvmw->page) >= hpage_nr_pages(pvmw->page))
 108                 return false;
 109
 110         return true;
 111 }
 112
 113 static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
 114 {
 115         pvmw->address = (pvmw->address + size) & ~(size - 1);
 116         if (!pvmw->address)
 117                 pvmw->address = ULONG_MAX;
 118 }
 119
 120 /**
 121  * page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
 122  * @pvmw->address
 123  * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
 124  * must be set. pmd, pte and ptl must be NULL.
 125  *
 126  * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
 127  * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
 128  * adjusted if needed (for PTE-mapped THPs).
 129  *
 130  * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
 131  * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
 132  * a loop to find all PTEs that map the THP.
 133  *
 134  * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
 135  * regardless of which page table level the page is mapped at. @pvmw->pmd is
 136  * NULL.
 137  *
 138  * Retruns false if there are no more page table entries for the page in
 139  * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
 140  *
 141  * If you need to stop the walk before page_vma_mapped_walk() returned false,
 142  * use page_vma_mapped_walk_done(). It will do the housekeeping.
 143  */
 144 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 145 {
 146         struct mm_struct *mm = pvmw->vma->vm_mm;
 147         struct page *page = pvmw->page;
 148         unsigned long end;
 149         pgd_t *pgd;
 150         p4d_t *p4d;
 151         pud_t *pud;
 152         pmd_t pmde;
 153
 154         /* The only possible pmd mapping has been handled on last iteration */
 155         if (pvmw->pmd && !pvmw->pte)
 156                 return not_found(pvmw);
 157
 158         if (unlikely(PageHuge(page))) {
 159                 /* The only possible mapping was handled on last iteration */
 160                 if (pvmw->pte)
 161                         return not_found(pvmw);
 162
 163                 /* when pud is not present, pte will be NULL */
 164                 pvmw->pte = huge_pte_offset(mm, pvmw->address,
 165                                             PAGE_SIZE << compound_order(page));
 166                 if (!pvmw->pte)
 167                         return false;
 168
 169                 pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
 170                 spin_lock(pvmw->ptl);
 171                 if (!check_pte(pvmw))
 172                         return not_found(pvmw);
 173                 return true;
 174         }
 175
 176         /*
 177          * Seek to next pte only makes sense for THP.
 178          * But more important than that optimization, is to filter out
 179          * any PageKsm page: whose page->index misleads vma_address()
 180          * and vma_address_end() to disaster.
 181          */
 182         end = PageTransCompound(page) ?
 183                 vma_address_end(page, pvmw->vma) :
 184                 pvmw->address + PAGE_SIZE;
 185         if (pvmw->pte)
 186                 goto next_pte;
 187 restart:
 188         do {
 189                 pgd = pgd_offset(mm, pvmw->address);
 190                 if (!pgd_present(*pgd)) {
 191                         step_forward(pvmw, PGDIR_SIZE);
 192                         continue;
 193                 }
 194                 p4d = p4d_offset(pgd, pvmw->address);
 195                 if (!p4d_present(*p4d)) {
 196                         step_forward(pvmw, P4D_SIZE);
 197                         continue;
 198                 }
 199                 pud = pud_offset(p4d, pvmw->address);
 200                 if (!pud_present(*pud)) {
 201                         step_forward(pvmw, PUD_SIZE);
 202                         continue;
 203                 }
 204
 205                 pvmw->pmd = pmd_offset(pud, pvmw->address);
 206                 /*
 207                  * Make sure the pmd value isn't cached in a register by the
 208                  * compiler and used as a stale value after we've observed a
 209                  * subsequent update.
 210                  */
 211                 pmde = READ_ONCE(*pvmw->pmd);
 212
 213                 if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
 214                         pvmw->ptl = pmd_lock(mm, pvmw->pmd);
 215                         pmde = *pvmw->pmd;
 216                         if (likely(pmd_trans_huge(pmde))) {
 217                                 if (pvmw->flags & PVMW_MIGRATION)
 218                                         return not_found(pvmw);
 219                                 if (pmd_page(pmde) != page)
 220                                         return not_found(pvmw);
 221                                 return true;
 222                         }
 223                         if (!pmd_present(pmde)) {
 224                                 swp_entry_t entry;
 225
 226                                 if (!thp_migration_supported() ||
 227                                     !(pvmw->flags & PVMW_MIGRATION))
 228                                         return not_found(pvmw);
 229                                 entry = pmd_to_swp_entry(pmde);
 230                                 if (!is_migration_entry(entry) ||
 231                                     migration_entry_to_page(entry) != page)
 232                                         return not_found(pvmw);
 233                                 return true;
 234                         }
 235                         /* THP pmd was split under us: handle on pte level */
 236                         spin_unlock(pvmw->ptl);
 237                         pvmw->ptl = NULL;
 238                 } else if (!pmd_present(pmde)) {
 239                         /*
 240                          * If PVMW_SYNC, take and drop THP pmd lock so that we
 241                          * cannot return prematurely, while zap_huge_pmd() has
 242                          * cleared *pmd but not decremented compound_mapcount().
 243                          */
 244                         if ((pvmw->flags & PVMW_SYNC) &&
 245                             PageTransCompound(page)) {
 246                                 spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);
 247
 248                                 spin_unlock(ptl);
 249                         }
 250                         step_forward(pvmw, PMD_SIZE);
 251                         continue;
 252                 }
 253                 if (!map_pte(pvmw))
 254                         goto next_pte;
 255 this_pte:
 256                 if (check_pte(pvmw))
 257                         return true;
 258 next_pte:
 259                 do {
 260                         pvmw->address += PAGE_SIZE;
 261                         if (pvmw->address >= end)
 262                                 return not_found(pvmw);
 263                         /* Did we cross page table boundary? */
 264                         if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {
 265                                 if (pvmw->ptl) {
 266                                         spin_unlock(pvmw->ptl);
 267                                         pvmw->ptl = NULL;
 268                                 }
 269                                 pte_unmap(pvmw->pte);
 270                                 pvmw->pte = NULL;
 271                                 goto restart;
 272                         }
 273                         pvmw->pte++;
 274                         if ((pvmw->flags & PVMW_SYNC) && !pvmw->ptl) {
 275                                 pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
 276                                 spin_lock(pvmw->ptl);
 277                         }
 278                 } while (pte_none(*pvmw->pte));
 279
 280                 if (!pvmw->ptl) {
 281                         pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
 282                         spin_lock(pvmw->ptl);
 283                 }
 284                 goto this_pte;
 285         } while (pvmw->address < end);
 286
 287         return false;
 288 }
 289
 290 /**
 291  * page_mapped_in_vma - check whether a page is really mapped in a VMA
 292  * @page: the page to test
 293  * @vma: the VMA to test
 294  *
 295  * Returns 1 if the page is mapped into the page tables of the VMA, 0
 296  * if the page is not mapped into the page tables of this VMA.  Only
 297  * valid for normal file or anonymous VMAs.
 298  */
 299 int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
 300 {
 301         struct page_vma_mapped_walk pvmw = {
 302                 .page = page,
 303                 .vma = vma,
 304                 .flags = PVMW_SYNC,
 305         };
 306
 307         pvmw.address = vma_address(page, vma);
 308         if (pvmw.address == -EFAULT)
 309                 return 0;
 310         if (!page_vma_mapped_walk(&pvmw))
 311                 return 0;
 312         page_vma_mapped_walk_done(&pvmw);
 313         return 1;
 314 }