LXR linux/mm/mincore.c

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 *      linux/mm/mincore.c
   4 *
   5 * Copyright (C) 1994-2006  Linus Torvalds
   6 */
   7
   8/*
   9 * The mincore() system call.
  10 */
  11#include <linux/pagemap.h>
  12#include <linux/gfp.h>
  13#include <linux/pagewalk.h>
  14#include <linux/mman.h>
  15#include <linux/syscalls.h>
  16#include <linux/swap.h>
  17#include <linux/swapops.h>
  18#include <linux/shmem_fs.h>
  19#include <linux/hugetlb.h>
  20#include <linux/pgtable.h>
  21
  22#include <linux/uaccess.h>
  23#include "swap.h"
  24
  25static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
  26                        unsigned long end, struct mm_walk *walk)
  27{
  28#ifdef CONFIG_HUGETLB_PAGE
  29        unsigned char present;
  30        unsigned char *vec = walk->private;
  31
  32        /*
  33         * Hugepages under user process are always in RAM and never
  34         * swapped out, but theoretically it needs to be checked.
  35         */
  36        present = pte && !huge_pte_none(huge_ptep_get(pte));
  37        for (; addr != end; vec++, addr += PAGE_SIZE)
  38                *vec = present;
  39        walk->private = vec;
  40#else
  41        BUG();
  42#endif
  43        return 0;
  44}
  45
  46/*
  47 * Later we can get more picky about what "in core" means precisely.
  48 * For now, simply check to see if the page is in the page cache,
  49 * and is up to date; i.e. that no page-in operation would be required
  50 * at this time if an application were to map and access this page.
  51 */
  52static unsigned char mincore_page(struct address_space *mapping, pgoff_t index)
  53{
  54        unsigned char present = 0;
  55        struct page *page;
  56
  57        /*
  58         * When tmpfs swaps out a page from a file, any process mapping that
  59         * file will not get a swp_entry_t in its pte, but rather it is like
  60         * any other file mapping (ie. marked !present and faulted in with
  61         * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
  62         */
  63        page = find_get_incore_page(mapping, index);
  64        if (page) {
  65                present = PageUptodate(page);
  66                put_page(page);
  67        }
  68
  69        return present;
  70}
  71
  72static int __mincore_unmapped_range(unsigned long addr, unsigned long end,
  73                                struct vm_area_struct *vma, unsigned char *vec)
  74{
  75        unsigned long nr = (end - addr) >> PAGE_SHIFT;
  76        int i;
  77
  78        if (vma->vm_file) {
  79                pgoff_t pgoff;
  80
  81                pgoff = linear_page_index(vma, addr);
  82                for (i = 0; i < nr; i++, pgoff++)
  83                        vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
  84        } else {
  85                for (i = 0; i < nr; i++)
  86                        vec[i] = 0;
  87        }
  88        return nr;
  89}
  90
  91static int mincore_unmapped_range(unsigned long addr, unsigned long end,
  92                                   __always_unused int depth,
  93                                   struct mm_walk *walk)
  94{
  95        walk->private += __mincore_unmapped_range(addr, end,
  96                                                  walk->vma, walk->private);
  97        return 0;
  98}
  99
 100static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 101                        struct mm_walk *walk)
 102{
 103        spinlock_t *ptl;
 104        struct vm_area_struct *vma = walk->vma;
 105        pte_t *ptep;
 106        unsigned char *vec = walk->private;
 107        int nr = (end - addr) >> PAGE_SHIFT;
 108
 109        ptl = pmd_trans_huge_lock(pmd, vma);
 110        if (ptl) {
 111                memset(vec, 1, nr);
 112                spin_unlock(ptl);
 113                goto out;
 114        }
 115
 116        if (pmd_trans_unstable(pmd)) {
 117                __mincore_unmapped_range(addr, end, vma, vec);
 118                goto out;
 119        }
 120
 121        ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
 122        for (; addr != end; ptep++, addr += PAGE_SIZE) {
 123                pte_t pte = *ptep;
 124
 125                /* We need to do cache lookup too for pte markers */
 126                if (pte_none_mostly(pte))
 127                        __mincore_unmapped_range(addr, addr + PAGE_SIZE,
 128                                                 vma, vec);
 129                else if (pte_present(pte))
 130                        *vec = 1;
 131                else { /* pte is a swap entry */
 132                        swp_entry_t entry = pte_to_swp_entry(pte);
 133
 134                        if (non_swap_entry(entry)) {
 135                                /*
 136                                 * migration or hwpoison entries are always
 137                                 * uptodate
 138                                 */
 139                                *vec = 1;
 140                        } else {
 141#ifdef CONFIG_SWAP
 142                                *vec = mincore_page(swap_address_space(entry),
 143                                                    swp_offset(entry));
 144#else
 145                                WARN_ON(1);
 146                                *vec = 1;
 147#endif
 148                        }
 149                }
 150                vec++;
 151        }
 152        pte_unmap_unlock(ptep - 1, ptl);
 153out:
 154        walk->private += nr;
 155        cond_resched();
 156        return 0;
 157}
 158
 159static inline bool can_do_mincore(struct vm_area_struct *vma)
 160{
 161        if (vma_is_anonymous(vma))
 162                return true;
 163        if (!vma->vm_file)
 164                return false;
 165        /*
 166         * Reveal pagecache information only for non-anonymous mappings that
 167         * correspond to the files the calling process could (if tried) open
 168         * for writing; otherwise we'd be including shared non-exclusive
 169         * mappings, which opens a side channel.
 170         */
 171        return inode_owner_or_capable(&init_user_ns,
 172                                      file_inode(vma->vm_file)) ||
 173               file_permission(vma->vm_file, MAY_WRITE) == 0;
 174}
 175
 176static const struct mm_walk_ops mincore_walk_ops = {
 177        .pmd_entry              = mincore_pte_range,
 178        .pte_hole               = mincore_unmapped_range,
 179        .hugetlb_entry          = mincore_hugetlb,
 180};
 181
 182/*
 183 * Do a chunk of "sys_mincore()". We've already checked
 184 * all the arguments, we hold the mmap semaphore: we should
 185 * just return the amount of info we're asked for.
 186 */
 187static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
 188{
 189        struct vm_area_struct *vma;
 190        unsigned long end;
 191        int err;
 192
 193        vma = find_vma(current->mm, addr);
 194        if (!vma || addr < vma->vm_start)
 195                return -ENOMEM;
 196        end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
 197        if (!can_do_mincore(vma)) {
 198                unsigned long pages = DIV_ROUND_UP(end - addr, PAGE_SIZE);
 199                memset(vec, 1, pages);
 200                return pages;
 201        }
 202        err = walk_page_range(vma->vm_mm, addr, end, &mincore_walk_ops, vec);
 203        if (err < 0)
 204                return err;
 205        return (end - addr) >> PAGE_SHIFT;
 206}
 207
 208/*
 209 * The mincore(2) system call.
 210 *
 211 * mincore() returns the memory residency status of the pages in the
 212 * current process's address space specified by [addr, addr + len).
 213 * The status is returned in a vector of bytes.  The least significant
 214 * bit of each byte is 1 if the referenced page is in memory, otherwise
 215 * it is zero.
 216 *
 217 * Because the status of a page can change after mincore() checks it
 218 * but before it returns to the application, the returned vector may
 219 * contain stale information.  Only locked pages are guaranteed to
 220 * remain in memory.
 221 *
 222 * return values:
 223 *  zero    - success
 224 *  -EFAULT - vec points to an illegal address
 225 *  -EINVAL - addr is not a multiple of PAGE_SIZE
 226 *  -ENOMEM - Addresses in the range [addr, addr + len] are
 227 *              invalid for the address space of this process, or
 228 *              specify one or more pages which are not currently
 229 *              mapped
 230 *  -EAGAIN - A kernel resource was temporarily unavailable.
 231 */
 232SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
 233                unsigned char __user *, vec)
 234{
 235        long retval;
 236        unsigned long pages;
 237        unsigned char *tmp;
 238
 239        start = untagged_addr(start);
 240
 241        /* Check the start address: needs to be page-aligned.. */
 242        if (start & ~PAGE_MASK)
 243                return -EINVAL;
 244
 245        /* ..and we need to be passed a valid user-space range */
 246        if (!access_ok((void __user *) start, len))
 247                return -ENOMEM;
 248
 249        /* This also avoids any overflows on PAGE_ALIGN */
 250        pages = len >> PAGE_SHIFT;
 251        pages += (offset_in_page(len)) != 0;
 252
 253        if (!access_ok(vec, pages))
 254                return -EFAULT;
 255
 256        tmp = (void *) __get_free_page(GFP_USER);
 257        if (!tmp)
 258                return -EAGAIN;
 259
 260        retval = 0;
 261        while (pages) {
 262                /*
 263                 * Do at most PAGE_SIZE entries per iteration, due to
 264                 * the temporary buffer size.
 265                 */
 266                mmap_read_lock(current->mm);
 267                retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
 268                mmap_read_unlock(current->mm);
 269
 270                if (retval <= 0)
 271                        break;
 272                if (copy_to_user(vec, tmp, retval)) {
 273                        retval = -EFAULT;
 274                        break;
 275                }
 276                pages -= retval;
 277                vec += retval;
 278                start += retval << PAGE_SHIFT;
 279                retval = 0;
 280        }
 281        free_page((unsigned long) tmp);
 282        return retval;
 283}
 284