mm/pagewalk.c

   1 #include <linux/mm.h>
   2 #include <linux/highmem.h>
   3 #include <linux/sched.h>
   4 #include <linux/hugetlb.h>
   5
   6 static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
   7                           struct mm_walk *walk)
   8 {
   9         pte_t *pte;
  10         int err = 0;
  11
  12         pte = pte_offset_map(pmd, addr);
  13         for (;;) {
  14                 err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
  15                 if (err)
  16                        break;
  17                 addr += PAGE_SIZE;
  18                 if (addr == end)
  19                         break;
  20                 pte++;
  21         }
  22
  23         pte_unmap(pte);
  24         return err;
  25 }
  26
  27 static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
  28                           struct mm_walk *walk)
  29 {
  30         pmd_t *pmd;
  31         unsigned long next;
  32         int err = 0;
  33
  34         pmd = pmd_offset(pud, addr);
  35         do {
  36 again:
  37                 next = pmd_addr_end(addr, end);
  38                 if (pmd_none(*pmd) || !walk->vma) {
  39                         if (walk->pte_hole)
  40                                 err = walk->pte_hole(addr, next, walk);
  41                         if (err)
  42                                 break;
  43                         continue;
  44                 }
  45                 /*
  46                  * This implies that each ->pmd_entry() handler
  47                  * needs to know about pmd_trans_huge() pmds
  48                  */
  49                 if (walk->pmd_entry)
  50                         err = walk->pmd_entry(pmd, addr, next, walk);
  51                 if (err)
  52                         break;
  53
  54                 /*
  55                  * Check this here so we only break down trans_huge
  56                  * pages when we _need_ to
  57                  */
  58                 if (!walk->pte_entry)
  59                         continue;
  60
  61                 split_huge_page_pmd_mm(walk->mm, addr, pmd);
  62                 if (pmd_trans_unstable(pmd))
  63                         goto again;
  64                 err = walk_pte_range(pmd, addr, next, walk);
  65                 if (err)
  66                         break;
  67         } while (pmd++, addr = next, addr != end);
  68
  69         return err;
  70 }
  71
  72 static int walk_pud_range(pgd_t *pgd, unsigned long addr, unsigned long end,
  73                           struct mm_walk *walk)
  74 {
  75         pud_t *pud;
  76         unsigned long next;
  77         int err = 0;
  78
  79         pud = pud_offset(pgd, addr);
  80         do {
  81                 next = pud_addr_end(addr, end);
  82                 if (pud_none_or_clear_bad(pud)) {
  83                         if (walk->pte_hole)
  84                                 err = walk->pte_hole(addr, next, walk);
  85                         if (err)
  86                                 break;
  87                         continue;
  88                 }
  89                 if (walk->pmd_entry || walk->pte_entry)
  90                         err = walk_pmd_range(pud, addr, next, walk);
  91                 if (err)
  92                         break;
  93         } while (pud++, addr = next, addr != end);
  94
  95         return err;
  96 }
  97
  98 static int walk_pgd_range(unsigned long addr, unsigned long end,
  99                           struct mm_walk *walk)
 100 {
 101         pgd_t *pgd;
 102         unsigned long next;
 103         int err = 0;
 104
 105         pgd = pgd_offset(walk->mm, addr);
 106         do {
 107                 next = pgd_addr_end(addr, end);
 108                 if (pgd_none_or_clear_bad(pgd)) {
 109                         if (walk->pte_hole)
 110                                 err = walk->pte_hole(addr, next, walk);
 111                         if (err)
 112                                 break;
 113                         continue;
 114                 }
 115                 if (walk->pmd_entry || walk->pte_entry)
 116                         err = walk_pud_range(pgd, addr, next, walk);
 117                 if (err)
 118                         break;
 119         } while (pgd++, addr = next, addr != end);
 120
 121         return err;
 122 }
 123
 124 #ifdef CONFIG_HUGETLB_PAGE
 125 static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
 126                                        unsigned long end)
 127 {
 128         unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
 129         return boundary < end ? boundary : end;
 130 }
 131
 132 static int walk_hugetlb_range(unsigned long addr, unsigned long end,
 133                               struct mm_walk *walk)
 134 {
 135         struct vm_area_struct *vma = walk->vma;
 136         struct hstate *h = hstate_vma(vma);
 137         unsigned long next;
 138         unsigned long hmask = huge_page_mask(h);
 139         pte_t *pte;
 140         int err = 0;
 141
 142         do {
 143                 next = hugetlb_entry_end(h, addr, end);
 144                 pte = huge_pte_offset(walk->mm, addr & hmask);
 145                 if (pte && walk->hugetlb_entry)
 146                         err = walk->hugetlb_entry(pte, hmask, addr, next, walk);
 147                 if (err)
 148                         break;
 149         } while (addr = next, addr != end);
 150
 151         return err;
 152 }
 153
 154 #else /* CONFIG_HUGETLB_PAGE */
 155 static int walk_hugetlb_range(unsigned long addr, unsigned long end,
 156                               struct mm_walk *walk)
 157 {
 158         return 0;
 159 }
 160
 161 #endif /* CONFIG_HUGETLB_PAGE */
 162
 163 /*
 164  * Decide whether we really walk over the current vma on [@start, @end)
 165  * or skip it via the returned value. Return 0 if we do walk over the
 166  * current vma, and return 1 if we skip the vma. Negative values means
 167  * error, where we abort the current walk.
 168  */
 169 static int walk_page_test(unsigned long start, unsigned long end,
 170                         struct mm_walk *walk)
 171 {
 172         struct vm_area_struct *vma = walk->vma;
 173
 174         if (walk->test_walk)
 175                 return walk->test_walk(start, end, walk);
 176
 177         /*
 178          * vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP
 179          * range, so we don't walk over it as we do for normal vmas. However,
 180          * Some callers are interested in handling hole range and they don't
 181          * want to just ignore any single address range. Such users certainly
 182          * define their ->pte_hole() callbacks, so let's delegate them to handle
 183          * vma(VM_PFNMAP).
 184          */
 185         if (vma->vm_flags & VM_PFNMAP) {
 186                 int err = 1;
 187                 if (walk->pte_hole)
 188                         err = walk->pte_hole(start, end, walk);
 189                 return err ? err : 1;
 190         }
 191         return 0;
 192 }
 193
 194 static int __walk_page_range(unsigned long start, unsigned long end,
 195                         struct mm_walk *walk)
 196 {
 197         int err = 0;
 198         struct vm_area_struct *vma = walk->vma;
 199
 200         if (vma && is_vm_hugetlb_page(vma)) {
 201                 if (walk->hugetlb_entry)
 202                         err = walk_hugetlb_range(start, end, walk);
 203         } else
 204                 err = walk_pgd_range(start, end, walk);
 205
 206         return err;
 207 }
 208
 209 /**
 210  * walk_page_range - walk page table with caller specific callbacks
 211  *
 212  * Recursively walk the page table tree of the process represented by @walk->mm
 213  * within the virtual address range [@start, @end). During walking, we can do
 214  * some caller-specific works for each entry, by setting up pmd_entry(),
 215  * pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these
 216  * callbacks, the associated entries/pages are just ignored.
 217  * The return values of these callbacks are commonly defined like below:
 218  *  - 0  : succeeded to handle the current entry, and if you don't reach the
 219  *         end address yet, continue to walk.
 220  *  - >0 : succeeded to handle the current entry, and return to the caller
 221  *         with caller specific value.
 222  *  - <0 : failed to handle the current entry, and return to the caller
 223  *         with error code.
 224  *
 225  * Before starting to walk page table, some callers want to check whether
 226  * they really want to walk over the current vma, typically by checking
 227  * its vm_flags. walk_page_test() and @walk->test_walk() are used for this
 228  * purpose.
 229  *
 230  * struct mm_walk keeps current values of some common data like vma and pmd,
 231  * which are useful for the access from callbacks. If you want to pass some
 232  * caller-specific data to callbacks, @walk->private should be helpful.
 233  *
 234  * Locking:
 235  *   Callers of walk_page_range() and walk_page_vma() should hold
 236  *   @walk->mm->mmap_sem, because these function traverse vma list and/or
 237  *   access to vma's data.
 238  */
 239 int walk_page_range(unsigned long start, unsigned long end,
 240                     struct mm_walk *walk)
 241 {
 242         int err = 0;
 243         unsigned long next;
 244         struct vm_area_struct *vma;
 245
 246         if (start >= end)
 247                 return -EINVAL;
 248
 249         if (!walk->mm)
 250                 return -EINVAL;
 251
 252         VM_BUG_ON_MM(!rwsem_is_locked(&walk->mm->mmap_sem), walk->mm);
 253
 254         vma = find_vma(walk->mm, start);
 255         do {
 256                 if (!vma) { /* after the last vma */
 257                         walk->vma = NULL;
 258                         next = end;
 259                 } else if (start < vma->vm_start) { /* outside vma */
 260                         walk->vma = NULL;
 261                         next = min(end, vma->vm_start);
 262                 } else { /* inside vma */
 263                         walk->vma = vma;
 264                         next = min(end, vma->vm_end);
 265                         vma = vma->vm_next;
 266
 267                         err = walk_page_test(start, next, walk);
 268                         if (err > 0) {
 269                                 /*
 270                                  * positive return values are purely for
 271                                  * controlling the pagewalk, so should never
 272                                  * be passed to the callers.
 273                                  */
 274                                 err = 0;
 275                                 continue;
 276                         }
 277                         if (err < 0)
 278                                 break;
 279                 }
 280                 if (walk->vma || walk->pte_hole)
 281                         err = __walk_page_range(start, next, walk);
 282                 if (err)
 283                         break;
 284         } while (start = next, start < end);
 285         return err;
 286 }
 287
 288 int walk_page_vma(struct vm_area_struct *vma, struct mm_walk *walk)
 289 {
 290         int err;
 291
 292         if (!walk->mm)
 293                 return -EINVAL;
 294
 295         VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));
 296         VM_BUG_ON(!vma);
 297         walk->vma = vma;
 298         err = walk_page_test(vma->vm_start, vma->vm_end, walk);
 299         if (err > 0)
 300                 return 0;
 301         if (err < 0)
 302                 return err;
 303         return __walk_page_range(vma->vm_start, vma->vm_end, walk);
 304 }