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

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