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

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