LXR linux/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 */
  27static 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 */
  56static 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
 143none_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 */
 180asmlinkage 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}
 230