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/slab.h>
  11 #include <linux/pagemap.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
  18 #include <asm/uaccess.h>
  19 #include <asm/pgtable.h>
  20
  21 /*
  22  * Later we can get more picky about what "in core" means precisely.
  23  * For now, simply check to see if the page is in the page cache,
  24  * and is up to date; i.e. that no page-in operation would be required
  25  * at this time if an application were to map and access this page.
  26  */
  27 static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
  28 {
  29         unsigned char present = 0;
  30         struct page *page;
  31
  32         /*
  33          * When tmpfs swaps out a page from a file, any process mapping that
  34          * file will not get a swp_entry_t in its pte, but rather it is like
  35          * any other file mapping (ie. marked !present and faulted in with
  36          * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
  37          *
  38          * However when tmpfs moves the page from pagecache and into swapcache,
  39          * it is still in core, but the find_get_page below won't find it.
  40          * No big deal, but make a note of it.
  41          */
  42         page = find_get_page(mapping, pgoff);
  43         if (page) {
  44                 present = PageUptodate(page);
  45                 page_cache_release(page);
  46         }
  47
  48         return present;
  49 }
  50
  51 /*
  52  * Do a chunk of "sys_mincore()". We've already checked
  53  * all the arguments, we hold the mmap semaphore: we should
  54  * just return the amount of info we're asked for.
  55  */
  56 static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages)
  57 {
  58         pgd_t *pgd;
  59         pud_t *pud;
  60         pmd_t *pmd;
  61         pte_t *ptep;
  62         spinlock_t *ptl;
  63         unsigned long nr;
  64         int i;
  65         pgoff_t pgoff;
  66         struct vm_area_struct *vma = find_vma(current->mm, addr);
  67
  68         /*
  69          * find_vma() didn't find anything above us, or we're
  70          * in an unmapped hole in the address space: ENOMEM.
  71          */
  72         if (!vma || addr < vma->vm_start)
  73                 return -ENOMEM;
  74
  75         /*
  76          * Calculate how many pages there are left in the last level of the
  77          * PTE array for our address.
  78          */
  79         nr = PTRS_PER_PTE - ((addr >> PAGE_SHIFT) & (PTRS_PER_PTE-1));
  80
  81         /*
  82          * Don't overrun this vma
  83          */
  84         nr = min(nr, (vma->vm_end - addr) >> PAGE_SHIFT);
  85
  86         /*
  87          * Don't return more than the caller asked for
  88          */
  89         nr = min(nr, pages);
  90
  91         pgd = pgd_offset(vma->vm_mm, addr);
  92         if (pgd_none_or_clear_bad(pgd))
  93                 goto none_mapped;
  94         pud = pud_offset(pgd, addr);
  95         if (pud_none_or_clear_bad(pud))
  96                 goto none_mapped;
  97         pmd = pmd_offset(pud, addr);
  98         if (pmd_none_or_clear_bad(pmd))
  99                 goto none_mapped;
 100
 101         ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 102         for (i = 0; i < nr; i++, ptep++, addr += PAGE_SIZE) {
 103                 unsigned char present;
 104                 pte_t pte = *ptep;
 105
 106                 if (pte_present(pte)) {
 107                         present = 1;
 108
 109                 } else if (pte_none(pte)) {
 110                         if (vma->vm_file) {
 111                                 pgoff = linear_page_index(vma, addr);
 112                                 present = mincore_page(vma->vm_file->f_mapping,
 113                                                         pgoff);
 114                         } else
 115                                 present = 0;
 116
 117                 } else if (pte_file(pte)) {
 118                         pgoff = pte_to_pgoff(pte);
 119                         present = mincore_page(vma->vm_file->f_mapping, pgoff);
 120
 121                 } else { /* pte is a swap entry */
 122                         swp_entry_t entry = pte_to_swp_entry(pte);
 123                         if (is_migration_entry(entry)) {
 124                                 /* migration entries are always uptodate */
 125                                 present = 1;
 126                         } else {
 127 #ifdef CONFIG_SWAP
 128                                 pgoff = entry.val;
 129                                 present = mincore_page(&swapper_space, pgoff);
 130 #else
 131                                 WARN_ON(1);
 132                                 present = 1;
 133 #endif
 134                         }
 135                 }
 136
 137                 vec[i] = present;
 138         }
 139         pte_unmap_unlock(ptep-1, ptl);
 140
 141         return nr;
 142
 143 none_mapped:
 144         if (vma->vm_file) {
 145                 pgoff = linear_page_index(vma, addr);
 146                 for (i = 0; i < nr; i++, pgoff++)
 147                         vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
 148         } else {
 149                 for (i = 0; i < nr; i++)
 150                         vec[i] = 0;
 151         }
 152
 153         return nr;
 154 }
 155
 156 /*
 157  * The mincore(2) system call.
 158  *
 159  * mincore() returns the memory residency status of the pages in the
 160  * current process's address space specified by [addr, addr + len).
 161  * The status is returned in a vector of bytes.  The least significant
 162  * bit of each byte is 1 if the referenced page is in memory, otherwise
 163  * it is zero.
 164  *
 165  * Because the status of a page can change after mincore() checks it
 166  * but before it returns to the application, the returned vector may
 167  * contain stale information.  Only locked pages are guaranteed to
 168  * remain in memory.
 169  *
 170  * return values:
 171  *  zero    - success
 172  *  -EFAULT - vec points to an illegal address
 173  *  -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE
 174  *  -ENOMEM - Addresses in the range [addr, addr + len] are
 175  *              invalid for the address space of this process, or
 176  *              specify one or more pages which are not currently
 177  *              mapped
 178  *  -EAGAIN - A kernel resource was temporarily unavailable.
 179  */
 180 asmlinkage long sys_mincore(unsigned long start, size_t len,
 181         unsigned char __user * vec)
 182 {
 183         long retval;
 184         unsigned long pages;
 185         unsigned char *tmp;
 186
 187         /* Check the start address: needs to be page-aligned.. */
 188         if (start & ~PAGE_CACHE_MASK)
 189                 return -EINVAL;
 190
 191         /* ..and we need to be passed a valid user-space range */
 192         if (!access_ok(VERIFY_READ, (void __user *) start, len))
 193                 return -ENOMEM;
 194
 195         /* This also avoids any overflows on PAGE_CACHE_ALIGN */
 196         pages = len >> PAGE_SHIFT;
 197         pages += (len & ~PAGE_MASK) != 0;
 198
 199         if (!access_ok(VERIFY_WRITE, vec, pages))
 200                 return -EFAULT;
 201
 202         tmp = (void *) __get_free_page(GFP_USER);
 203         if (!tmp)
 204                 return -EAGAIN;
 205
 206         retval = 0;
 207         while (pages) {
 208                 /*
 209                  * Do at most PAGE_SIZE entries per iteration, due to
 210                  * the temporary buffer size.
 211                  */
 212                 down_read(&current->mm->mmap_sem);
 213                 retval = do_mincore(start, tmp, min(pages, PAGE_SIZE));
 214                 up_read(&current->mm->mmap_sem);
 215
 216                 if (retval <= 0)
 217                         break;
 218                 if (copy_to_user(vec, tmp, retval)) {
 219                         retval = -EFAULT;
 220                         break;
 221                 }
 222                 pages -= retval;
 223                 vec += retval;
 224                 start += retval << PAGE_SHIFT;
 225                 retval = 0;
 226         }
 227         free_page((unsigned long) tmp);
 228         return retval;
 229 }