Root/mm/fremap.c

1/*
2 * linux/mm/fremap.c
3 *
4 * Explicit pagetable population and nonlinear (random) mappings support.
5 *
6 * started by Ingo Molnar, Copyright (C) 2002, 2003
7 */
8#include <linux/export.h>
9#include <linux/backing-dev.h>
10#include <linux/mm.h>
11#include <linux/swap.h>
12#include <linux/file.h>
13#include <linux/mman.h>
14#include <linux/pagemap.h>
15#include <linux/swapops.h>
16#include <linux/rmap.h>
17#include <linux/syscalls.h>
18#include <linux/mmu_notifier.h>
19
20#include <asm/mmu_context.h>
21#include <asm/cacheflush.h>
22#include <asm/tlbflush.h>
23
24#include "internal.h"
25
26static int mm_counter(struct page *page)
27{
28    return PageAnon(page) ? MM_ANONPAGES : MM_FILEPAGES;
29}
30
31static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
32            unsigned long addr, pte_t *ptep)
33{
34    pte_t pte = *ptep;
35    struct page *page;
36    swp_entry_t entry;
37
38    if (pte_present(pte)) {
39        flush_cache_page(vma, addr, pte_pfn(pte));
40        pte = ptep_clear_flush(vma, addr, ptep);
41        page = vm_normal_page(vma, addr, pte);
42        if (page) {
43            if (pte_dirty(pte))
44                set_page_dirty(page);
45            update_hiwater_rss(mm);
46            dec_mm_counter(mm, mm_counter(page));
47            page_remove_rmap(page);
48            page_cache_release(page);
49        }
50    } else { /* zap_pte() is not called when pte_none() */
51        if (!pte_file(pte)) {
52            update_hiwater_rss(mm);
53            entry = pte_to_swp_entry(pte);
54            if (non_swap_entry(entry)) {
55                if (is_migration_entry(entry)) {
56                    page = migration_entry_to_page(entry);
57                    dec_mm_counter(mm, mm_counter(page));
58                }
59            } else {
60                free_swap_and_cache(entry);
61                dec_mm_counter(mm, MM_SWAPENTS);
62            }
63        }
64        pte_clear_not_present_full(mm, addr, ptep, 0);
65    }
66}
67
68/*
69 * Install a file pte to a given virtual memory address, release any
70 * previously existing mapping.
71 */
72static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
73        unsigned long addr, unsigned long pgoff, pgprot_t prot)
74{
75    int err = -ENOMEM;
76    pte_t *pte, ptfile;
77    spinlock_t *ptl;
78
79    pte = get_locked_pte(mm, addr, &ptl);
80    if (!pte)
81        goto out;
82
83    ptfile = pgoff_to_pte(pgoff);
84
85    if (!pte_none(*pte))
86        zap_pte(mm, vma, addr, pte);
87
88    set_pte_at(mm, addr, pte, pte_file_mksoft_dirty(ptfile));
89    /*
90     * We don't need to run update_mmu_cache() here because the "file pte"
91     * being installed by install_file_pte() is not a real pte - it's a
92     * non-present entry (like a swap entry), noting what file offset should
93     * be mapped there when there's a fault (in a non-linear vma where
94     * that's not obvious).
95     */
96    pte_unmap_unlock(pte, ptl);
97    err = 0;
98out:
99    return err;
100}
101
102int generic_file_remap_pages(struct vm_area_struct *vma, unsigned long addr,
103                 unsigned long size, pgoff_t pgoff)
104{
105    struct mm_struct *mm = vma->vm_mm;
106    int err;
107
108    do {
109        err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
110        if (err)
111            return err;
112
113        size -= PAGE_SIZE;
114        addr += PAGE_SIZE;
115        pgoff++;
116    } while (size);
117
118    return 0;
119}
120EXPORT_SYMBOL(generic_file_remap_pages);
121
122/**
123 * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
124 * @start: start of the remapped virtual memory range
125 * @size: size of the remapped virtual memory range
126 * @prot: new protection bits of the range (see NOTE)
127 * @pgoff: to-be-mapped page of the backing store file
128 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
129 *
130 * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
131 * (shared backing store file).
132 *
133 * This syscall works purely via pagetables, so it's the most efficient
134 * way to map the same (large) file into a given virtual window. Unlike
135 * mmap()/mremap() it does not create any new vmas. The new mappings are
136 * also safe across swapout.
137 *
138 * NOTE: the @prot parameter right now is ignored (but must be zero),
139 * and the vma's default protection is used. Arbitrary protections
140 * might be implemented in the future.
141 */
142SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
143        unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
144{
145    struct mm_struct *mm = current->mm;
146    struct address_space *mapping;
147    struct vm_area_struct *vma;
148    int err = -EINVAL;
149    int has_write_lock = 0;
150    vm_flags_t vm_flags = 0;
151
152    pr_warn_once("%s (%d) uses deprecated remap_file_pages() syscall. "
153            "See Documentation/vm/remap_file_pages.txt.\n",
154            current->comm, current->pid);
155
156    if (prot)
157        return err;
158    /*
159     * Sanitize the syscall parameters:
160     */
161    start = start & PAGE_MASK;
162    size = size & PAGE_MASK;
163
164    /* Does the address range wrap, or is the span zero-sized? */
165    if (start + size <= start)
166        return err;
167
168    /* Does pgoff wrap? */
169    if (pgoff + (size >> PAGE_SHIFT) < pgoff)
170        return err;
171
172    /* Can we represent this offset inside this architecture's pte's? */
173#if PTE_FILE_MAX_BITS < BITS_PER_LONG
174    if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
175        return err;
176#endif
177
178    /* We need down_write() to change vma->vm_flags. */
179    down_read(&mm->mmap_sem);
180 retry:
181    vma = find_vma(mm, start);
182
183    /*
184     * Make sure the vma is shared, that it supports prefaulting,
185     * and that the remapped range is valid and fully within
186     * the single existing vma.
187     */
188    if (!vma || !(vma->vm_flags & VM_SHARED))
189        goto out;
190
191    if (!vma->vm_ops || !vma->vm_ops->remap_pages)
192        goto out;
193
194    if (start < vma->vm_start || start + size > vma->vm_end)
195        goto out;
196
197    /* Must set VM_NONLINEAR before any pages are populated. */
198    if (!(vma->vm_flags & VM_NONLINEAR)) {
199        /*
200         * vm_private_data is used as a swapout cursor
201         * in a VM_NONLINEAR vma.
202         */
203        if (vma->vm_private_data)
204            goto out;
205
206        /* Don't need a nonlinear mapping, exit success */
207        if (pgoff == linear_page_index(vma, start)) {
208            err = 0;
209            goto out;
210        }
211
212        if (!has_write_lock) {
213get_write_lock:
214            up_read(&mm->mmap_sem);
215            down_write(&mm->mmap_sem);
216            has_write_lock = 1;
217            goto retry;
218        }
219        mapping = vma->vm_file->f_mapping;
220        /*
221         * page_mkclean doesn't work on nonlinear vmas, so if
222         * dirty pages need to be accounted, emulate with linear
223         * vmas.
224         */
225        if (mapping_cap_account_dirty(mapping)) {
226            unsigned long addr;
227            struct file *file = get_file(vma->vm_file);
228            /* mmap_region may free vma; grab the info now */
229            vm_flags = vma->vm_flags;
230
231            addr = mmap_region(file, start, size, vm_flags, pgoff);
232            fput(file);
233            if (IS_ERR_VALUE(addr)) {
234                err = addr;
235            } else {
236                BUG_ON(addr != start);
237                err = 0;
238            }
239            goto out_freed;
240        }
241        mutex_lock(&mapping->i_mmap_mutex);
242        flush_dcache_mmap_lock(mapping);
243        vma->vm_flags |= VM_NONLINEAR;
244        vma_interval_tree_remove(vma, &mapping->i_mmap);
245        vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
246        flush_dcache_mmap_unlock(mapping);
247        mutex_unlock(&mapping->i_mmap_mutex);
248    }
249
250    if (vma->vm_flags & VM_LOCKED) {
251        /*
252         * drop PG_Mlocked flag for over-mapped range
253         */
254        if (!has_write_lock)
255            goto get_write_lock;
256        vm_flags = vma->vm_flags;
257        munlock_vma_pages_range(vma, start, start + size);
258        vma->vm_flags = vm_flags;
259    }
260
261    mmu_notifier_invalidate_range_start(mm, start, start + size);
262    err = vma->vm_ops->remap_pages(vma, start, size, pgoff);
263    mmu_notifier_invalidate_range_end(mm, start, start + size);
264
265    /*
266     * We can't clear VM_NONLINEAR because we'd have to do
267     * it after ->populate completes, and that would prevent
268     * downgrading the lock. (Locks can't be upgraded).
269     */
270
271out:
272    if (vma)
273        vm_flags = vma->vm_flags;
274out_freed:
275    if (likely(!has_write_lock))
276        up_read(&mm->mmap_sem);
277    else
278        up_write(&mm->mmap_sem);
279    if (!err && ((vm_flags & VM_LOCKED) || !(flags & MAP_NONBLOCK)))
280        mm_populate(start, size);
281
282    return err;
283}
284

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