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 <linux/uaccess.h>
  20 #include <asm/pgtable.h>
  21
  22 static 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  */
  49 static 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
  85 static 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
 104 static 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
 112 static 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);
 164 out:
 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  */
 175 static 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  */
 222 SYSCALL_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 }