Root/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
22/*
23 * Later we can get more picky about what "in core" means precisely.
24 * For now, simply check to see if the page is in the page cache,
25 * and is up to date; i.e. that no page-in operation would be required
26 * at this time if an application were to map and access this page.
27 */
28static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
29{
30    unsigned char present = 0;
31    struct page *page;
32
33    /*
34     * When tmpfs swaps out a page from a file, any process mapping that
35     * file will not get a swp_entry_t in its pte, but rather it is like
36     * any other file mapping (ie. marked !present and faulted in with
37     * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
38     *
39     * However when tmpfs moves the page from pagecache and into swapcache,
40     * it is still in core, but the find_get_page below won't find it.
41     * No big deal, but make a note of it.
42     */
43    page = find_get_page(mapping, pgoff);
44    if (page) {
45        present = PageUptodate(page);
46        page_cache_release(page);
47    }
48
49    return present;
50}
51
52/*
53 * Do a chunk of "sys_mincore()". We've already checked
54 * all the arguments, we hold the mmap semaphore: we should
55 * just return the amount of info we're asked for.
56 */
57static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages)
58{
59    pgd_t *pgd;
60    pud_t *pud;
61    pmd_t *pmd;
62    pte_t *ptep;
63    spinlock_t *ptl;
64    unsigned long nr;
65    int i;
66    pgoff_t pgoff;
67    struct vm_area_struct *vma = find_vma(current->mm, addr);
68
69    /*
70     * find_vma() didn't find anything above us, or we're
71     * in an unmapped hole in the address space: ENOMEM.
72     */
73    if (!vma || addr < vma->vm_start)
74        return -ENOMEM;
75
76#ifdef CONFIG_HUGETLB_PAGE
77    if (is_vm_hugetlb_page(vma)) {
78        struct hstate *h;
79        unsigned long nr_huge;
80        unsigned char present;
81
82        i = 0;
83        nr = min(pages, (vma->vm_end - addr) >> PAGE_SHIFT);
84        h = hstate_vma(vma);
85        nr_huge = ((addr + pages * PAGE_SIZE - 1) >> huge_page_shift(h))
86              - (addr >> huge_page_shift(h)) + 1;
87        nr_huge = min(nr_huge,
88                  (vma->vm_end - addr) >> huge_page_shift(h));
89        while (1) {
90            /* hugepage always in RAM for now,
91             * but generally it needs to be check */
92            ptep = huge_pte_offset(current->mm,
93                           addr & huge_page_mask(h));
94            present = !!(ptep &&
95                     !huge_pte_none(huge_ptep_get(ptep)));
96            while (1) {
97                vec[i++] = present;
98                addr += PAGE_SIZE;
99                /* reach buffer limit */
100                if (i == nr)
101                    return nr;
102                /* check hugepage border */
103                if (!((addr & ~huge_page_mask(h))
104                      >> PAGE_SHIFT))
105                    break;
106            }
107        }
108        return nr;
109    }
110#endif
111
112    /*
113     * Calculate how many pages there are left in the last level of the
114     * PTE array for our address.
115     */
116    nr = PTRS_PER_PTE - ((addr >> PAGE_SHIFT) & (PTRS_PER_PTE-1));
117
118    /*
119     * Don't overrun this vma
120     */
121    nr = min(nr, (vma->vm_end - addr) >> PAGE_SHIFT);
122
123    /*
124     * Don't return more than the caller asked for
125     */
126    nr = min(nr, pages);
127
128    pgd = pgd_offset(vma->vm_mm, addr);
129    if (pgd_none_or_clear_bad(pgd))
130        goto none_mapped;
131    pud = pud_offset(pgd, addr);
132    if (pud_none_or_clear_bad(pud))
133        goto none_mapped;
134    pmd = pmd_offset(pud, addr);
135    if (pmd_none_or_clear_bad(pmd))
136        goto none_mapped;
137
138    ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
139    for (i = 0; i < nr; i++, ptep++, addr += PAGE_SIZE) {
140        unsigned char present;
141        pte_t pte = *ptep;
142
143        if (pte_present(pte)) {
144            present = 1;
145
146        } else if (pte_none(pte)) {
147            if (vma->vm_file) {
148                pgoff = linear_page_index(vma, addr);
149                present = mincore_page(vma->vm_file->f_mapping,
150                            pgoff);
151            } else
152                present = 0;
153
154        } else if (pte_file(pte)) {
155            pgoff = pte_to_pgoff(pte);
156            present = mincore_page(vma->vm_file->f_mapping, pgoff);
157
158        } else { /* pte is a swap entry */
159            swp_entry_t entry = pte_to_swp_entry(pte);
160            if (is_migration_entry(entry)) {
161                /* migration entries are always uptodate */
162                present = 1;
163            } else {
164#ifdef CONFIG_SWAP
165                pgoff = entry.val;
166                present = mincore_page(&swapper_space, pgoff);
167#else
168                WARN_ON(1);
169                present = 1;
170#endif
171            }
172        }
173
174        vec[i] = present;
175    }
176    pte_unmap_unlock(ptep-1, ptl);
177
178    return nr;
179
180none_mapped:
181    if (vma->vm_file) {
182        pgoff = linear_page_index(vma, addr);
183        for (i = 0; i < nr; i++, pgoff++)
184            vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
185    } else {
186        for (i = 0; i < nr; i++)
187            vec[i] = 0;
188    }
189
190    return nr;
191}
192
193/*
194 * The mincore(2) system call.
195 *
196 * mincore() returns the memory residency status of the pages in the
197 * current process's address space specified by [addr, addr + len).
198 * The status is returned in a vector of bytes. The least significant
199 * bit of each byte is 1 if the referenced page is in memory, otherwise
200 * it is zero.
201 *
202 * Because the status of a page can change after mincore() checks it
203 * but before it returns to the application, the returned vector may
204 * contain stale information. Only locked pages are guaranteed to
205 * remain in memory.
206 *
207 * return values:
208 * zero - success
209 * -EFAULT - vec points to an illegal address
210 * -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE
211 * -ENOMEM - Addresses in the range [addr, addr + len] are
212 * invalid for the address space of this process, or
213 * specify one or more pages which are not currently
214 * mapped
215 * -EAGAIN - A kernel resource was temporarily unavailable.
216 */
217SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
218        unsigned char __user *, vec)
219{
220    long retval;
221    unsigned long pages;
222    unsigned char *tmp;
223
224    /* Check the start address: needs to be page-aligned.. */
225     if (start & ~PAGE_CACHE_MASK)
226        return -EINVAL;
227
228    /* ..and we need to be passed a valid user-space range */
229    if (!access_ok(VERIFY_READ, (void __user *) start, len))
230        return -ENOMEM;
231
232    /* This also avoids any overflows on PAGE_CACHE_ALIGN */
233    pages = len >> PAGE_SHIFT;
234    pages += (len & ~PAGE_MASK) != 0;
235
236    if (!access_ok(VERIFY_WRITE, vec, pages))
237        return -EFAULT;
238
239    tmp = (void *) __get_free_page(GFP_USER);
240    if (!tmp)
241        return -EAGAIN;
242
243    retval = 0;
244    while (pages) {
245        /*
246         * Do at most PAGE_SIZE entries per iteration, due to
247         * the temporary buffer size.
248         */
249        down_read(&current->mm->mmap_sem);
250        retval = do_mincore(start, tmp, min(pages, PAGE_SIZE));
251        up_read(&current->mm->mmap_sem);
252
253        if (retval <= 0)
254            break;
255        if (copy_to_user(vec, tmp, retval)) {
256            retval = -EFAULT;
257            break;
258        }
259        pages -= retval;
260        vec += retval;
261        start += retval << PAGE_SHIFT;
262        retval = 0;
263    }
264    free_page((unsigned long) tmp);
265    return retval;
266}
267

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