linux/mm/mincore.c
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   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
  22static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
  23                        unsigned long end, struct mm_walk *walk)
  24{
  25#ifdef CONFIG_HUGETLB_PAGE
  26        unsigned char present;
  27        unsigned char *vec = walk->private;
  28
  29        /*
  30         * Hugepages under user process are always in RAM and never
  31         * swapped out, but theoretically it needs to be checked.
  32         */
  33        present = pte && !huge_pte_none(huge_ptep_get(pte));
  34        for (; addr != end; vec++, addr += PAGE_SIZE)
  35                *vec = present;
  36        walk->private = vec;
  37#else
  38        BUG();
  39#endif
  40        return 0;
  41}
  42
  43/*
  44 * Later we can get more picky about what "in core" means precisely.
  45 * For now, simply check to see if the page is in the page cache,
  46 * and is up to date; i.e. that no page-in operation would be required
  47 * at this time if an application were to map and access this page.
  48 */
  49static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
  50{
  51        unsigned char present = 0;
  52        struct page *page;
  53
  54        /*
  55         * When tmpfs swaps out a page from a file, any process mapping that
  56         * file will not get a swp_entry_t in its pte, but rather it is like
  57         * any other file mapping (ie. marked !present and faulted in with
  58         * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
  59         */
  60#ifdef CONFIG_SWAP
  61        if (shmem_mapping(mapping)) {
  62                page = find_get_entry(mapping, pgoff);
  63                /*
  64                 * shmem/tmpfs may return swap: account for swapcache
  65                 * page too.
  66                 */
  67                if (radix_tree_exceptional_entry(page)) {
  68                        swp_entry_t swp = radix_to_swp_entry(page);
  69                        page = find_get_page(swap_address_space(swp),
  70                                             swp_offset(swp));
  71                }
  72        } else
  73                page = find_get_page(mapping, pgoff);
  74#else
  75        page = find_get_page(mapping, pgoff);
  76#endif
  77        if (page) {
  78                present = PageUptodate(page);
  79                put_page(page);
  80        }
  81
  82        return present;
  83}
  84
  85static int __mincore_unmapped_range(unsigned long addr, unsigned long end,
  86                                struct vm_area_struct *vma, unsigned char *vec)
  87{
  88        unsigned long nr = (end - addr) >> PAGE_SHIFT;
  89        int i;
  90
  91        if (vma->vm_file) {
  92                pgoff_t pgoff;
  93
  94                pgoff = linear_page_index(vma, addr);
  95                for (i = 0; i < nr; i++, pgoff++)
  96                        vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
  97        } else {
  98                for (i = 0; i < nr; i++)
  99                        vec[i] = 0;
 100        }
 101        return nr;
 102}
 103
 104static int mincore_unmapped_range(unsigned long addr, unsigned long end,
 105                                   struct mm_walk *walk)
 106{
 107        walk->private += __mincore_unmapped_range(addr, end,
 108                                                  walk->vma, walk->private);
 109        return 0;
 110}
 111
 112static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 113                        struct mm_walk *walk)
 114{
 115        spinlock_t *ptl;
 116        struct vm_area_struct *vma = walk->vma;
 117        pte_t *ptep;
 118        unsigned char *vec = walk->private;
 119        int nr = (end - addr) >> PAGE_SHIFT;
 120
 121        ptl = pmd_trans_huge_lock(pmd, vma);
 122        if (ptl) {
 123                memset(vec, 1, nr);
 124                spin_unlock(ptl);
 125                goto out;
 126        }
 127
 128        if (pmd_trans_unstable(pmd)) {
 129                __mincore_unmapped_range(addr, end, vma, vec);
 130                goto out;
 131        }
 132
 133        ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
 134        for (; addr != end; ptep++, addr += PAGE_SIZE) {
 135                pte_t pte = *ptep;
 136
 137                if (pte_none(pte))
 138                        __mincore_unmapped_range(addr, addr + PAGE_SIZE,
 139                                                 vma, vec);
 140                else if (pte_present(pte))
 141                        *vec = 1;
 142                else { /* pte is a swap entry */
 143                        swp_entry_t entry = pte_to_swp_entry(pte);
 144
 145                        if (non_swap_entry(entry)) {
 146                                /*
 147                                 * migration or hwpoison entries are always
 148                                 * uptodate
 149                                 */
 150                                *vec = 1;
 151                        } else {
 152#ifdef CONFIG_SWAP
 153                                *vec = mincore_page(swap_address_space(entry),
 154                                                    swp_offset(entry));
 155#else
 156                                WARN_ON(1);
 157                                *vec = 1;
 158#endif
 159                        }
 160                }
 161                vec++;
 162        }
 163        pte_unmap_unlock(ptep - 1, ptl);
 164out:
 165        walk->private += nr;
 166        cond_resched();
 167        return 0;
 168}
 169
 170/*
 171 * Do a chunk of "sys_mincore()". We've already checked
 172 * all the arguments, we hold the mmap semaphore: we should
 173 * just return the amount of info we're asked for.
 174 */
 175static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
 176{
 177        struct vm_area_struct *vma;
 178        unsigned long end;
 179        int err;
 180        struct mm_walk mincore_walk = {
 181                .pmd_entry = mincore_pte_range,
 182                .pte_hole = mincore_unmapped_range,
 183                .hugetlb_entry = mincore_hugetlb,
 184                .private = vec,
 185        };
 186
 187        vma = find_vma(current->mm, addr);
 188        if (!vma || addr < vma->vm_start)
 189                return -ENOMEM;
 190        mincore_walk.mm = vma->vm_mm;
 191        end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
 192        err = walk_page_range(addr, end, &mincore_walk);
 193        if (err < 0)
 194                return err;
 195        return (end - addr) >> PAGE_SHIFT;
 196}
 197
 198/*
 199 * The mincore(2) system call.
 200 *
 201 * mincore() returns the memory residency status of the pages in the
 202 * current process's address space specified by [addr, addr + len).
 203 * The status is returned in a vector of bytes.  The least significant
 204 * bit of each byte is 1 if the referenced page is in memory, otherwise
 205 * it is zero.
 206 *
 207 * Because the status of a page can change after mincore() checks it
 208 * but before it returns to the application, the returned vector may
 209 * contain stale information.  Only locked pages are guaranteed to
 210 * remain in memory.
 211 *
 212 * return values:
 213 *  zero    - success
 214 *  -EFAULT - vec points to an illegal address
 215 *  -EINVAL - addr is not a multiple of PAGE_SIZE
 216 *  -ENOMEM - Addresses in the range [addr, addr + len] are
 217 *              invalid for the address space of this process, or
 218 *              specify one or more pages which are not currently
 219 *              mapped
 220 *  -EAGAIN - A kernel resource was temporarily unavailable.
 221 */
 222SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
 223                unsigned char __user *, vec)
 224{
 225        long retval;
 226        unsigned long pages;
 227        unsigned char *tmp;
 228
 229        /* Check the start address: needs to be page-aligned.. */
 230        if (start & ~PAGE_MASK)
 231                return -EINVAL;
 232
 233        /* ..and we need to be passed a valid user-space range */
 234        if (!access_ok(VERIFY_READ, (void __user *) start, len))
 235                return -ENOMEM;
 236
 237        /* This also avoids any overflows on PAGE_ALIGN */
 238        pages = len >> PAGE_SHIFT;
 239        pages += (offset_in_page(len)) != 0;
 240
 241        if (!access_ok(VERIFY_WRITE, vec, pages))
 242                return -EFAULT;
 243
 244        tmp = (void *) __get_free_page(GFP_USER);
 245        if (!tmp)
 246                return -EAGAIN;
 247
 248        retval = 0;
 249        while (pages) {
 250                /*
 251                 * Do at most PAGE_SIZE entries per iteration, due to
 252                 * the temporary buffer size.
 253                 */
 254                down_read(&current->mm->mmap_sem);
 255                retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
 256                up_read(&current->mm->mmap_sem);
 257
 258                if (retval <= 0)
 259                        break;
 260                if (copy_to_user(vec, tmp, retval)) {
 261                        retval = -EFAULT;
 262                        break;
 263                }
 264                pages -= retval;
 265                vec += retval;
 266                start += retval << PAGE_SHIFT;
 267                retval = 0;
 268        }
 269        free_page((unsigned long) tmp);
 270        return retval;
 271}
 272