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 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
84int generic_file_remap_pages(struct vm_area_struct *vma, unsigned long addr,
85                 unsigned long size, pgoff_t pgoff)
86{
87    struct mm_struct *mm = vma->vm_mm;
88    int err;
89
90    do {
91        err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
92        if (err)
93            return err;
94
95        size -= PAGE_SIZE;
96        addr += PAGE_SIZE;
97        pgoff++;
98    } while (size);
99
100    return 0;
101}
102EXPORT_SYMBOL(generic_file_remap_pages);
103
104/**
105 * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
106 * @start: start of the remapped virtual memory range
107 * @size: size of the remapped virtual memory range
108 * @prot: new protection bits of the range (see NOTE)
109 * @pgoff: to-be-mapped page of the backing store file
110 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
111 *
112 * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
113 * (shared backing store file).
114 *
115 * This syscall works purely via pagetables, so it's the most efficient
116 * way to map the same (large) file into a given virtual window. Unlike
117 * mmap()/mremap() it does not create any new vmas. The new mappings are
118 * also safe across swapout.
119 *
120 * NOTE: the @prot parameter right now is ignored (but must be zero),
121 * and the vma's default protection is used. Arbitrary protections
122 * might be implemented in the future.
123 */
124SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
125        unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
126{
127    struct mm_struct *mm = current->mm;
128    struct address_space *mapping;
129    struct vm_area_struct *vma;
130    int err = -EINVAL;
131    int has_write_lock = 0;
132    vm_flags_t vm_flags = 0;
133
134    if (prot)
135        return err;
136    /*
137     * Sanitize the syscall parameters:
138     */
139    start = start & PAGE_MASK;
140    size = size & PAGE_MASK;
141
142    /* Does the address range wrap, or is the span zero-sized? */
143    if (start + size <= start)
144        return err;
145
146    /* Does pgoff wrap? */
147    if (pgoff + (size >> PAGE_SHIFT) < pgoff)
148        return err;
149
150    /* Can we represent this offset inside this architecture's pte's? */
151#if PTE_FILE_MAX_BITS < BITS_PER_LONG
152    if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
153        return err;
154#endif
155
156    /* We need down_write() to change vma->vm_flags. */
157    down_read(&mm->mmap_sem);
158 retry:
159    vma = find_vma(mm, start);
160
161    /*
162     * Make sure the vma is shared, that it supports prefaulting,
163     * and that the remapped range is valid and fully within
164     * the single existing vma.
165     */
166    if (!vma || !(vma->vm_flags & VM_SHARED))
167        goto out;
168
169    if (!vma->vm_ops || !vma->vm_ops->remap_pages)
170        goto out;
171
172    if (start < vma->vm_start || start + size > vma->vm_end)
173        goto out;
174
175    /* Must set VM_NONLINEAR before any pages are populated. */
176    if (!(vma->vm_flags & VM_NONLINEAR)) {
177        /*
178         * vm_private_data is used as a swapout cursor
179         * in a VM_NONLINEAR vma.
180         */
181        if (vma->vm_private_data)
182            goto out;
183
184        /* Don't need a nonlinear mapping, exit success */
185        if (pgoff == linear_page_index(vma, start)) {
186            err = 0;
187            goto out;
188        }
189
190        if (!has_write_lock) {
191get_write_lock:
192            up_read(&mm->mmap_sem);
193            down_write(&mm->mmap_sem);
194            has_write_lock = 1;
195            goto retry;
196        }
197        mapping = vma->vm_file->f_mapping;
198        /*
199         * page_mkclean doesn't work on nonlinear vmas, so if
200         * dirty pages need to be accounted, emulate with linear
201         * vmas.
202         */
203        if (mapping_cap_account_dirty(mapping)) {
204            unsigned long addr;
205            struct file *file = get_file(vma->vm_file);
206
207            addr = mmap_region(file, start, size,
208                    vma->vm_flags, pgoff);
209            fput(file);
210            if (IS_ERR_VALUE(addr)) {
211                err = addr;
212            } else {
213                BUG_ON(addr != start);
214                err = 0;
215            }
216            goto out;
217        }
218        mutex_lock(&mapping->i_mmap_mutex);
219        flush_dcache_mmap_lock(mapping);
220        vma->vm_flags |= VM_NONLINEAR;
221        vma_interval_tree_remove(vma, &mapping->i_mmap);
222        vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
223        flush_dcache_mmap_unlock(mapping);
224        mutex_unlock(&mapping->i_mmap_mutex);
225    }
226
227    if (vma->vm_flags & VM_LOCKED) {
228        /*
229         * drop PG_Mlocked flag for over-mapped range
230         */
231        if (!has_write_lock)
232            goto get_write_lock;
233        vm_flags = vma->vm_flags;
234        munlock_vma_pages_range(vma, start, start + size);
235        vma->vm_flags = vm_flags;
236    }
237
238    mmu_notifier_invalidate_range_start(mm, start, start + size);
239    err = vma->vm_ops->remap_pages(vma, start, size, pgoff);
240    mmu_notifier_invalidate_range_end(mm, start, start + size);
241
242    /*
243     * We can't clear VM_NONLINEAR because we'd have to do
244     * it after ->populate completes, and that would prevent
245     * downgrading the lock. (Locks can't be upgraded).
246     */
247
248out:
249    if (vma)
250        vm_flags = vma->vm_flags;
251    if (likely(!has_write_lock))
252        up_read(&mm->mmap_sem);
253    else
254        up_write(&mm->mmap_sem);
255    if (!err && ((vm_flags & VM_LOCKED) || !(flags & MAP_NONBLOCK)))
256        mm_populate(start, size);
257
258    return err;
259}
260

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