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 .nopage). 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         if (nr > pages)
  81                 nr = pages;
  82
  83         pgd = pgd_offset(vma->vm_mm, addr);
  84         if (pgd_none_or_clear_bad(pgd))
  85                 goto none_mapped;
  86         pud = pud_offset(pgd, addr);
  87         if (pud_none_or_clear_bad(pud))
  88                 goto none_mapped;
  89         pmd = pmd_offset(pud, addr);
  90         if (pmd_none_or_clear_bad(pmd))
  91                 goto none_mapped;
  92
  93         ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
  94         for (i = 0; i < nr; i++, ptep++, addr += PAGE_SIZE) {
  95                 unsigned char present;
  96                 pte_t pte = *ptep;
  97
  98                 if (pte_present(pte)) {
  99                         present = 1;
 100
 101                 } else if (pte_none(pte)) {
 102                         if (vma->vm_file) {
 103                                 pgoff = linear_page_index(vma, addr);
 104                                 present = mincore_page(vma->vm_file->f_mapping,
 105                                                         pgoff);
 106                         } else
 107                                 present = 0;
 108
 109                 } else if (pte_file(pte)) {
 110                         pgoff = pte_to_pgoff(pte);
 111                         present = mincore_page(vma->vm_file->f_mapping, pgoff);
 112
 113                 } else { /* pte is a swap entry */
 114                         swp_entry_t entry = pte_to_swp_entry(pte);
 115                         if (is_migration_entry(entry)) {
 116                                 /* migration entries are always uptodate */
 117                                 present = 1;
 118                         } else {
 119                                 pgoff = entry.val;
 120                                 present = mincore_page(&swapper_space, pgoff);
 121                         }
 122                 }
 123         }
 124         pte_unmap_unlock(ptep-1, ptl);
 125
 126         return nr;
 127
 128 none_mapped:
 129         if (vma->vm_file) {
 130                 pgoff = linear_page_index(vma, addr);
 131                 for (i = 0; i < nr; i++, pgoff++)
 132                         vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
 133         }
 134
 135         return nr;
 136 }
 137
 138 /*
 139  * The mincore(2) system call.
 140  *
 141  * mincore() returns the memory residency status of the pages in the
 142  * current process's address space specified by [addr, addr + len).
 143  * The status is returned in a vector of bytes.  The least significant
 144  * bit of each byte is 1 if the referenced page is in memory, otherwise
 145  * it is zero.
 146  *
 147  * Because the status of a page can change after mincore() checks it
 148  * but before it returns to the application, the returned vector may
 149  * contain stale information.  Only locked pages are guaranteed to
 150  * remain in memory.
 151  *
 152  * return values:
 153  *  zero    - success
 154  *  -EFAULT - vec points to an illegal address
 155  *  -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE
 156  *  -ENOMEM - Addresses in the range [addr, addr + len] are
 157  *              invalid for the address space of this process, or
 158  *              specify one or more pages which are not currently
 159  *              mapped
 160  *  -EAGAIN - A kernel resource was temporarily unavailable.
 161  */
 162 asmlinkage long sys_mincore(unsigned long start, size_t len,
 163         unsigned char __user * vec)
 164 {
 165         long retval;
 166         unsigned long pages;
 167         unsigned char *tmp;
 168
 169         /* Check the start address: needs to be page-aligned.. */
 170         if (start & ~PAGE_CACHE_MASK)
 171                 return -EINVAL;
 172
 173         /* ..and we need to be passed a valid user-space range */
 174         if (!access_ok(VERIFY_READ, (void __user *) start, len))
 175                 return -ENOMEM;
 176
 177         /* This also avoids any overflows on PAGE_CACHE_ALIGN */
 178         pages = len >> PAGE_SHIFT;
 179         pages += (len & ~PAGE_MASK) != 0;
 180
 181         if (!access_ok(VERIFY_WRITE, vec, pages))
 182                 return -EFAULT;
 183
 184         tmp = (void *) __get_free_page(GFP_USER);
 185         if (!tmp)
 186                 return -EAGAIN;
 187
 188         retval = 0;
 189         while (pages) {
 190                 /*
 191                  * Do at most PAGE_SIZE entries per iteration, due to
 192                  * the temporary buffer size.
 193                  */
 194                 down_read(&current->mm->mmap_sem);
 195                 retval = do_mincore(start, tmp, min(pages, PAGE_SIZE));
 196                 up_read(&current->mm->mmap_sem);
 197
 198                 if (retval <= 0)
 199                         break;
 200                 if (copy_to_user(vec, tmp, retval)) {
 201                         retval = -EFAULT;
 202                         break;
 203                 }
 204                 pages -= retval;
 205                 vec += retval;
 206                 start += retval << PAGE_SHIFT;
 207                 retval = 0;
 208         }
 209         free_page((unsigned long) tmp);
 210         return retval;
 211 }