mm/mincore.c

   1 /*
   2  *      linux/mm/mincore.c
   3  *
   4  * Copyright (C) 1994-2006  Linus Torvalds
   5  */
   6
   7 /*
   8  * The mincore() system call.
   9  */
  10 #include <linux/pagemap.h>
  11 #include <linux/gfp.h>
  12 #include <linux/mm.h>
  13 #include <linux/mman.h>
  14 #include <linux/syscalls.h>
  15 #include <linux/swap.h>
  16 #include <linux/swapops.h>
  17 #include <linux/hugetlb.h>
  18
  19 #include <asm/uaccess.h>
  20 #include <asm/pgtable.h>
  21
  22 static void mincore_hugetlb_page_range(struct vm_area_struct *vma,
  23                                 unsigned long addr, unsigned long end,
  24                                 unsigned char *vec)
  25 {
  26 #ifdef CONFIG_HUGETLB_PAGE
  27         struct hstate *h;
  28
  29         h = hstate_vma(vma);
  30         while (1) {
  31                 unsigned char present;
  32                 pte_t *ptep;
  33                 /*
  34                  * Huge pages are always in RAM for now, but
  35                  * theoretically it needs to be checked.
  36                  */
  37                 ptep = huge_pte_offset(current->mm,
  38                                        addr & huge_page_mask(h));
  39                 present = ptep && !huge_pte_none(huge_ptep_get(ptep));
  40                 while (1) {
  41                         *vec = present;
  42                         vec++;
  43                         addr += PAGE_SIZE;
  44                         if (addr == end)
  45                                 return;
  46                         /* check hugepage border */
  47                         if (!(addr & ~huge_page_mask(h)))
  48                                 break;
  49                 }
  50         }
  51 #else
  52         BUG();
  53 #endif
  54 }
  55
  56 /*
  57  * Later we can get more picky about what "in core" means precisely.
  58  * For now, simply check to see if the page is in the page cache,
  59  * and is up to date; i.e. that no page-in operation would be required
  60  * at this time if an application were to map and access this page.
  61  */
  62 static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
  63 {
  64         unsigned char present = 0;
  65         struct page *page;
  66
  67         /*
  68          * When tmpfs swaps out a page from a file, any process mapping that
  69          * file will not get a swp_entry_t in its pte, but rather it is like
  70          * any other file mapping (ie. marked !present and faulted in with
  71          * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
  72          */
  73         page = find_get_page(mapping, pgoff);
  74 #ifdef CONFIG_SWAP
  75         /* shmem/tmpfs may return swap: account for swapcache page too. */
  76         if (radix_tree_exceptional_entry(page)) {
  77                 swp_entry_t swap = radix_to_swp_entry(page);
  78                 page = find_get_page(swap_address_space(swap), swap.val);
  79         }
  80 #endif
  81         if (page) {
  82                 present = PageUptodate(page);
  83                 page_cache_release(page);
  84         }
  85
  86         return present;
  87 }
  88
  89 static void mincore_unmapped_range(struct vm_area_struct *vma,
  90                                 unsigned long addr, unsigned long end,
  91                                 unsigned char *vec)
  92 {
  93         unsigned long nr = (end - addr) >> PAGE_SHIFT;
  94         int i;
  95
  96         if (vma->vm_file) {
  97                 pgoff_t pgoff;
  98
  99                 pgoff = linear_page_index(vma, addr);
 100                 for (i = 0; i < nr; i++, pgoff++)
 101                         vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
 102         } else {
 103                 for (i = 0; i < nr; i++)
 104                         vec[i] = 0;
 105         }
 106 }
 107
 108 static void mincore_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 109                         unsigned long addr, unsigned long end,
 110                         unsigned char *vec)
 111 {
 112         unsigned long next;
 113         spinlock_t *ptl;
 114         pte_t *ptep;
 115
 116         ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 117         do {
 118                 pte_t pte = *ptep;
 119                 pgoff_t pgoff;
 120
 121                 next = addr + PAGE_SIZE;
 122                 if (pte_none(pte))
 123                         mincore_unmapped_range(vma, addr, next, vec);
 124                 else if (pte_present(pte))
 125                         *vec = 1;
 126                 else if (pte_file(pte)) {
 127                         pgoff = pte_to_pgoff(pte);
 128                         *vec = mincore_page(vma->vm_file->f_mapping, pgoff);
 129                 } else { /* pte is a swap entry */
 130                         swp_entry_t entry = pte_to_swp_entry(pte);
 131
 132                         if (is_migration_entry(entry)) {
 133                                 /* migration entries are always uptodate */
 134                                 *vec = 1;
 135                         } else {
 136 #ifdef CONFIG_SWAP
 137                                 pgoff = entry.val;
 138                                 *vec = mincore_page(swap_address_space(entry),
 139                                         pgoff);
 140 #else
 141                                 WARN_ON(1);
 142                                 *vec = 1;
 143 #endif
 144                         }
 145                 }
 146                 vec++;
 147         } while (ptep++, addr = next, addr != end);
 148         pte_unmap_unlock(ptep - 1, ptl);
 149 }
 150
 151 static void mincore_pmd_range(struct vm_area_struct *vma, pud_t *pud,
 152                         unsigned long addr, unsigned long end,
 153                         unsigned char *vec)
 154 {
 155         unsigned long next;
 156         pmd_t *pmd;
 157
 158         pmd = pmd_offset(pud, addr);
 159         do {
 160                 next = pmd_addr_end(addr, end);
 161                 if (pmd_trans_huge(*pmd)) {
 162                         if (mincore_huge_pmd(vma, pmd, addr, next, vec)) {
 163                                 vec += (next - addr) >> PAGE_SHIFT;
 164                                 continue;
 165                         }
 166                         /* fall through */
 167                 }
 168                 if (pmd_none_or_trans_huge_or_clear_bad(pmd))
 169                         mincore_unmapped_range(vma, addr, next, vec);
 170                 else
 171                         mincore_pte_range(vma, pmd, addr, next, vec);
 172                 vec += (next - addr) >> PAGE_SHIFT;
 173         } while (pmd++, addr = next, addr != end);
 174 }
 175
 176 static void mincore_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
 177                         unsigned long addr, unsigned long end,
 178                         unsigned char *vec)
 179 {
 180         unsigned long next;
 181         pud_t *pud;
 182
 183         pud = pud_offset(pgd, addr);
 184         do {
 185                 next = pud_addr_end(addr, end);
 186                 if (pud_none_or_clear_bad(pud))
 187                         mincore_unmapped_range(vma, addr, next, vec);
 188                 else
 189                         mincore_pmd_range(vma, pud, addr, next, vec);
 190                 vec += (next - addr) >> PAGE_SHIFT;
 191         } while (pud++, addr = next, addr != end);
 192 }
 193
 194 static void mincore_page_range(struct vm_area_struct *vma,
 195                         unsigned long addr, unsigned long end,
 196                         unsigned char *vec)
 197 {
 198         unsigned long next;
 199         pgd_t *pgd;
 200
 201         pgd = pgd_offset(vma->vm_mm, addr);
 202         do {
 203                 next = pgd_addr_end(addr, end);
 204                 if (pgd_none_or_clear_bad(pgd))
 205                         mincore_unmapped_range(vma, addr, next, vec);
 206                 else
 207                         mincore_pud_range(vma, pgd, addr, next, vec);
 208                 vec += (next - addr) >> PAGE_SHIFT;
 209         } while (pgd++, addr = next, addr != end);
 210 }
 211
 212 /*
 213  * Do a chunk of "sys_mincore()". We've already checked
 214  * all the arguments, we hold the mmap semaphore: we should
 215  * just return the amount of info we're asked for.
 216  */
 217 static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
 218 {
 219         struct vm_area_struct *vma;
 220         unsigned long end;
 221
 222         vma = find_vma(current->mm, addr);
 223         if (!vma || addr < vma->vm_start)
 224                 return -ENOMEM;
 225
 226         end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
 227
 228         if (is_vm_hugetlb_page(vma))
 229                 mincore_hugetlb_page_range(vma, addr, end, vec);
 230         else
 231                 mincore_page_range(vma, addr, end, vec);
 232
 233         return (end - addr) >> PAGE_SHIFT;
 234 }
 235
 236 /*
 237  * The mincore(2) system call.
 238  *
 239  * mincore() returns the memory residency status of the pages in the
 240  * current process's address space specified by [addr, addr + len).
 241  * The status is returned in a vector of bytes.  The least significant
 242  * bit of each byte is 1 if the referenced page is in memory, otherwise
 243  * it is zero.
 244  *
 245  * Because the status of a page can change after mincore() checks it
 246  * but before it returns to the application, the returned vector may
 247  * contain stale information.  Only locked pages are guaranteed to
 248  * remain in memory.
 249  *
 250  * return values:
 251  *  zero    - success
 252  *  -EFAULT - vec points to an illegal address
 253  *  -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE
 254  *  -ENOMEM - Addresses in the range [addr, addr + len] are
 255  *              invalid for the address space of this process, or
 256  *              specify one or more pages which are not currently
 257  *              mapped
 258  *  -EAGAIN - A kernel resource was temporarily unavailable.
 259  */
 260 SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
 261                 unsigned char __user *, vec)
 262 {
 263         long retval;
 264         unsigned long pages;
 265         unsigned char *tmp;
 266
 267         /* Check the start address: needs to be page-aligned.. */
 268         if (start & ~PAGE_CACHE_MASK)
 269                 return -EINVAL;
 270
 271         /* ..and we need to be passed a valid user-space range */
 272         if (!access_ok(VERIFY_READ, (void __user *) start, len))
 273                 return -ENOMEM;
 274
 275         /* This also avoids any overflows on PAGE_CACHE_ALIGN */
 276         pages = len >> PAGE_SHIFT;
 277         pages += (len & ~PAGE_MASK) != 0;
 278
 279         if (!access_ok(VERIFY_WRITE, vec, pages))
 280                 return -EFAULT;
 281
 282         tmp = (void *) __get_free_page(GFP_USER);
 283         if (!tmp)
 284                 return -EAGAIN;
 285
 286         retval = 0;
 287         while (pages) {
 288                 /*
 289                  * Do at most PAGE_SIZE entries per iteration, due to
 290                  * the temporary buffer size.
 291                  */
 292                 down_read(&current->mm->mmap_sem);
 293                 retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
 294                 up_read(&current->mm->mmap_sem);
 295
 296                 if (retval <= 0)
 297                         break;
 298                 if (copy_to_user(vec, tmp, retval)) {
 299                         retval = -EFAULT;
 300                         break;
 301                 }
 302                 pages -= retval;
 303                 vec += retval;
 304                 start += retval << PAGE_SHIFT;
 305                 retval = 0;
 306         }
 307         free_page((unsigned long) tmp);
 308         return retval;
 309 }