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/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), swp.val);
  70                }
  71        } else
  72                page = find_get_page(mapping, pgoff);
  73#else
  74        page = find_get_page(mapping, pgoff);
  75#endif
  76        if (page) {
  77                present = PageUptodate(page);
  78                put_page(page);
  79        }
  80
  81        return present;
  82}
  83
  84static int __mincore_unmapped_range(unsigned long addr, unsigned long end,
  85                                struct vm_area_struct *vma, unsigned char *vec)
  86{
  87        unsigned long nr = (end - addr) >> PAGE_SHIFT;
  88        int i;
  89
  90        if (vma->vm_file) {
  91                pgoff_t pgoff;
  92
  93                pgoff = linear_page_index(vma, addr);
  94                for (i = 0; i < nr; i++, pgoff++)
  95                        vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
  96        } else {
  97                for (i = 0; i < nr; i++)
  98                        vec[i] = 0;
  99        }
 100        return nr;
 101}
 102
 103static int mincore_unmapped_range(unsigned long addr, unsigned long end,
 104                                   struct mm_walk *walk)
 105{
 106        walk->private += __mincore_unmapped_range(addr, end,
 107                                                  walk->vma, walk->private);
 108        return 0;
 109}
 110
 111static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 112                        struct mm_walk *walk)
 113{
 114        spinlock_t *ptl;
 115        struct vm_area_struct *vma = walk->vma;
 116        pte_t *ptep;
 117        unsigned char *vec = walk->private;
 118        int nr = (end - addr) >> PAGE_SHIFT;
 119
 120        ptl = pmd_trans_huge_lock(pmd, vma);
 121        if (ptl) {
 122                memset(vec, 1, nr);
 123                spin_unlock(ptl);
 124                goto out;
 125        }
 126
 127        if (pmd_trans_unstable(pmd)) {
 128                __mincore_unmapped_range(addr, end, vma, vec);
 129                goto out;
 130        }
 131
 132        ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
 133        for (; addr != end; ptep++, addr += PAGE_SIZE) {
 134                pte_t pte = *ptep;
 135
 136                if (pte_none(pte))
 137                        __mincore_unmapped_range(addr, addr + PAGE_SIZE,
 138                                                 vma, vec);
 139                else if (pte_present(pte))
 140                        *vec = 1;
 141                else { /* pte is a swap entry */
 142                        swp_entry_t entry = pte_to_swp_entry(pte);
 143
 144                        if (non_swap_entry(entry)) {
 145                                /*
 146                                 * migration or hwpoison entries are always
 147                                 * uptodate
 148                                 */
 149                                *vec = 1;
 150                        } else {
 151#ifdef CONFIG_SWAP
 152                                *vec = mincore_page(swap_address_space(entry),
 153                                        entry.val);
 154#else
 155                                WARN_ON(1);
 156                                *vec = 1;
 157#endif
 158                        }
 159                }
 160                vec++;
 161        }
 162        pte_unmap_unlock(ptep - 1, ptl);
 163out:
 164        walk->private += nr;
 165        cond_resched();
 166        return 0;
 167}
 168
 169/*
 170 * Do a chunk of "sys_mincore()". We've already checked
 171 * all the arguments, we hold the mmap semaphore: we should
 172 * just return the amount of info we're asked for.
 173 */
 174static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
 175{
 176        struct vm_area_struct *vma;
 177        unsigned long end;
 178        int err;
 179        struct mm_walk mincore_walk = {
 180                .pmd_entry = mincore_pte_range,
 181                .pte_hole = mincore_unmapped_range,
 182                .hugetlb_entry = mincore_hugetlb,
 183                .private = vec,
 184        };
 185
 186        vma = find_vma(current->mm, addr);
 187        if (!vma || addr < vma->vm_start)
 188                return -ENOMEM;
 189        mincore_walk.mm = vma->vm_mm;
 190        end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
 191        err = walk_page_range(addr, end, &mincore_walk);
 192        if (err < 0)
 193                return err;
 194        return (end - addr) >> PAGE_SHIFT;
 195}
 196
 197/*
 198 * The mincore(2) system call.
 199 *
 200 * mincore() returns the memory residency status of the pages in the
 201 * current process's address space specified by [addr, addr + len).
 202 * The status is returned in a vector of bytes.  The least significant
 203 * bit of each byte is 1 if the referenced page is in memory, otherwise
 204 * it is zero.
 205 *
 206 * Because the status of a page can change after mincore() checks it
 207 * but before it returns to the application, the returned vector may
 208 * contain stale information.  Only locked pages are guaranteed to
 209 * remain in memory.
 210 *
 211 * return values:
 212 *  zero    - success
 213 *  -EFAULT - vec points to an illegal address
 214 *  -EINVAL - addr is not a multiple of PAGE_SIZE
 215 *  -ENOMEM - Addresses in the range [addr, addr + len] are
 216 *              invalid for the address space of this process, or
 217 *              specify one or more pages which are not currently
 218 *              mapped
 219 *  -EAGAIN - A kernel resource was temporarily unavailable.
 220 */
 221SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
 222                unsigned char __user *, vec)
 223{
 224        long retval;
 225        unsigned long pages;
 226        unsigned char *tmp;
 227
 228        /* Check the start address: needs to be page-aligned.. */
 229        if (start & ~PAGE_MASK)
 230                return -EINVAL;
 231
 232        /* ..and we need to be passed a valid user-space range */
 233        if (!access_ok(VERIFY_READ, (void __user *) start, len))
 234                return -ENOMEM;
 235
 236        /* This also avoids any overflows on PAGE_ALIGN */
 237        pages = len >> PAGE_SHIFT;
 238        pages += (offset_in_page(len)) != 0;
 239
 240        if (!access_ok(VERIFY_WRITE, vec, pages))
 241                return -EFAULT;
 242
 243        tmp = (void *) __get_free_page(GFP_USER);
 244        if (!tmp)
 245                return -EAGAIN;
 246
 247        retval = 0;
 248        while (pages) {
 249                /*
 250                 * Do at most PAGE_SIZE entries per iteration, due to
 251                 * the temporary buffer size.
 252                 */
 253                down_read(&current->mm->mmap_sem);
 254                retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
 255                up_read(&current->mm->mmap_sem);
 256
 257                if (retval <= 0)
 258                        break;
 259                if (copy_to_user(vec, tmp, retval)) {
 260                        retval = -EFAULT;
 261                        break;
 262                }
 263                pages -= retval;
 264                vec += retval;
 265                start += retval << PAGE_SHIFT;
 266                retval = 0;
 267        }
 268        free_page((unsigned long) tmp);
 269        return retval;
 270}
 271