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
22static void mincore_hugetlb_page_range(struct vm_area_struct *vma,
23                unsigned long addr, unsigned long end,
24                unsigned char *vec)
25{
26#ifdef CONFIG_HUGETLB_PAGE
27    struct hstate *h;
28
29    h = hstate_vma(vma);
30    while (1) {
31        unsigned char present;
32        pte_t *ptep;
33        /*
34         * Huge pages are always in RAM for now, but
35         * theoretically it needs to be checked.
36         */
37        ptep = huge_pte_offset(current->mm,
38                       addr & huge_page_mask(h));
39        present = ptep && !huge_pte_none(huge_ptep_get(ptep));
40        while (1) {
41            *vec = present;
42            vec++;
43            addr += PAGE_SIZE;
44            if (addr == end)
45                return;
46            /* check hugepage border */
47            if (!(addr & ~huge_page_mask(h)))
48                break;
49        }
50    }
51#else
52    BUG();
53#endif
54}
55
56/*
57 * Later we can get more picky about what "in core" means precisely.
58 * For now, simply check to see if the page is in the page cache,
59 * and is up to date; i.e. that no page-in operation would be required
60 * at this time if an application were to map and access this page.
61 */
62static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
63{
64    unsigned char present = 0;
65    struct page *page;
66
67    /*
68     * When tmpfs swaps out a page from a file, any process mapping that
69     * file will not get a swp_entry_t in its pte, but rather it is like
70     * any other file mapping (ie. marked !present and faulted in with
71     * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
72     *
73     * However when tmpfs moves the page from pagecache and into swapcache,
74     * it is still in core, but the find_get_page below won't find it.
75     * No big deal, but make a note of it.
76     */
77    page = find_get_page(mapping, pgoff);
78    if (page) {
79        present = PageUptodate(page);
80        page_cache_release(page);
81    }
82
83    return present;
84}
85
86static void mincore_unmapped_range(struct vm_area_struct *vma,
87                unsigned long addr, unsigned long end,
88                unsigned char *vec)
89{
90    unsigned long nr = (end - addr) >> PAGE_SHIFT;
91    int i;
92
93    if (vma->vm_file) {
94        pgoff_t pgoff;
95
96        pgoff = linear_page_index(vma, addr);
97        for (i = 0; i < nr; i++, pgoff++)
98            vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
99    } else {
100        for (i = 0; i < nr; i++)
101            vec[i] = 0;
102    }
103}
104
105static void mincore_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
106            unsigned long addr, unsigned long end,
107            unsigned char *vec)
108{
109    unsigned long next;
110    spinlock_t *ptl;
111    pte_t *ptep;
112
113    ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
114    do {
115        pte_t pte = *ptep;
116        pgoff_t pgoff;
117
118        next = addr + PAGE_SIZE;
119        if (pte_none(pte))
120            mincore_unmapped_range(vma, addr, next, vec);
121        else if (pte_present(pte))
122            *vec = 1;
123        else if (pte_file(pte)) {
124            pgoff = pte_to_pgoff(pte);
125            *vec = mincore_page(vma->vm_file->f_mapping, pgoff);
126        } else { /* pte is a swap entry */
127            swp_entry_t entry = pte_to_swp_entry(pte);
128
129            if (is_migration_entry(entry)) {
130                /* migration entries are always uptodate */
131                *vec = 1;
132            } else {
133#ifdef CONFIG_SWAP
134                pgoff = entry.val;
135                *vec = mincore_page(&swapper_space, pgoff);
136#else
137                WARN_ON(1);
138                *vec = 1;
139#endif
140            }
141        }
142        vec++;
143    } while (ptep++, addr = next, addr != end);
144    pte_unmap_unlock(ptep - 1, ptl);
145}
146
147static void mincore_pmd_range(struct vm_area_struct *vma, pud_t *pud,
148            unsigned long addr, unsigned long end,
149            unsigned char *vec)
150{
151    unsigned long next;
152    pmd_t *pmd;
153
154    pmd = pmd_offset(pud, addr);
155    do {
156        next = pmd_addr_end(addr, end);
157        if (pmd_none_or_clear_bad(pmd))
158            mincore_unmapped_range(vma, addr, next, vec);
159        else
160            mincore_pte_range(vma, pmd, addr, next, vec);
161        vec += (next - addr) >> PAGE_SHIFT;
162    } while (pmd++, addr = next, addr != end);
163}
164
165static void mincore_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
166            unsigned long addr, unsigned long end,
167            unsigned char *vec)
168{
169    unsigned long next;
170    pud_t *pud;
171
172    pud = pud_offset(pgd, addr);
173    do {
174        next = pud_addr_end(addr, end);
175        if (pud_none_or_clear_bad(pud))
176            mincore_unmapped_range(vma, addr, next, vec);
177        else
178            mincore_pmd_range(vma, pud, addr, next, vec);
179        vec += (next - addr) >> PAGE_SHIFT;
180    } while (pud++, addr = next, addr != end);
181}
182
183static void mincore_page_range(struct vm_area_struct *vma,
184            unsigned long addr, unsigned long end,
185            unsigned char *vec)
186{
187    unsigned long next;
188    pgd_t *pgd;
189
190    pgd = pgd_offset(vma->vm_mm, addr);
191    do {
192        next = pgd_addr_end(addr, end);
193        if (pgd_none_or_clear_bad(pgd))
194            mincore_unmapped_range(vma, addr, next, vec);
195        else
196            mincore_pud_range(vma, pgd, addr, next, vec);
197        vec += (next - addr) >> PAGE_SHIFT;
198    } while (pgd++, addr = next, addr != end);
199}
200
201/*
202 * Do a chunk of "sys_mincore()". We've already checked
203 * all the arguments, we hold the mmap semaphore: we should
204 * just return the amount of info we're asked for.
205 */
206static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
207{
208    struct vm_area_struct *vma;
209    unsigned long end;
210
211    vma = find_vma(current->mm, addr);
212    if (!vma || addr < vma->vm_start)
213        return -ENOMEM;
214
215    end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
216
217    if (is_vm_hugetlb_page(vma)) {
218        mincore_hugetlb_page_range(vma, addr, end, vec);
219        return (end - addr) >> PAGE_SHIFT;
220    }
221
222    end = pmd_addr_end(addr, end);
223
224    if (is_vm_hugetlb_page(vma))
225        mincore_hugetlb_page_range(vma, addr, end, vec);
226    else
227        mincore_page_range(vma, addr, end, vec);
228
229    return (end - addr) >> PAGE_SHIFT;
230}
231
232/*
233 * The mincore(2) system call.
234 *
235 * mincore() returns the memory residency status of the pages in the
236 * current process's address space specified by [addr, addr + len).
237 * The status is returned in a vector of bytes. The least significant
238 * bit of each byte is 1 if the referenced page is in memory, otherwise
239 * it is zero.
240 *
241 * Because the status of a page can change after mincore() checks it
242 * but before it returns to the application, the returned vector may
243 * contain stale information. Only locked pages are guaranteed to
244 * remain in memory.
245 *
246 * return values:
247 * zero - success
248 * -EFAULT - vec points to an illegal address
249 * -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE
250 * -ENOMEM - Addresses in the range [addr, addr + len] are
251 * invalid for the address space of this process, or
252 * specify one or more pages which are not currently
253 * mapped
254 * -EAGAIN - A kernel resource was temporarily unavailable.
255 */
256SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
257        unsigned char __user *, vec)
258{
259    long retval;
260    unsigned long pages;
261    unsigned char *tmp;
262
263    /* Check the start address: needs to be page-aligned.. */
264     if (start & ~PAGE_CACHE_MASK)
265        return -EINVAL;
266
267    /* ..and we need to be passed a valid user-space range */
268    if (!access_ok(VERIFY_READ, (void __user *) start, len))
269        return -ENOMEM;
270
271    /* This also avoids any overflows on PAGE_CACHE_ALIGN */
272    pages = len >> PAGE_SHIFT;
273    pages += (len & ~PAGE_MASK) != 0;
274
275    if (!access_ok(VERIFY_WRITE, vec, pages))
276        return -EFAULT;
277
278    tmp = (void *) __get_free_page(GFP_USER);
279    if (!tmp)
280        return -EAGAIN;
281
282    retval = 0;
283    while (pages) {
284        /*
285         * Do at most PAGE_SIZE entries per iteration, due to
286         * the temporary buffer size.
287         */
288        down_read(&current->mm->mmap_sem);
289        retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
290        up_read(&current->mm->mmap_sem);
291
292        if (retval <= 0)
293            break;
294        if (copy_to_user(vec, tmp, retval)) {
295            retval = -EFAULT;
296            break;
297        }
298        pages -= retval;
299        vec += retval;
300        start += retval << PAGE_SHIFT;
301        retval = 0;
302    }
303    free_page((unsigned long) tmp);
304    return retval;
305}
306

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