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, ptfile;
61    spinlock_t *ptl;
62
63    pte = get_locked_pte(mm, addr, &ptl);
64    if (!pte)
65        goto out;
66
67    ptfile = pgoff_to_pte(pgoff);
68
69    if (!pte_none(*pte)) {
70        if (pte_present(*pte) && pte_soft_dirty(*pte))
71            pte_file_mksoft_dirty(ptfile);
72        zap_pte(mm, vma, addr, pte);
73    }
74
75    set_pte_at(mm, addr, pte, ptfile);
76    /*
77     * We don't need to run update_mmu_cache() here because the "file pte"
78     * being installed by install_file_pte() is not a real pte - it's a
79     * non-present entry (like a swap entry), noting what file offset should
80     * be mapped there when there's a fault (in a non-linear vma where
81     * that's not obvious).
82     */
83    pte_unmap_unlock(pte, ptl);
84    err = 0;
85out:
86    return err;
87}
88
89int generic_file_remap_pages(struct vm_area_struct *vma, unsigned long addr,
90                 unsigned long size, pgoff_t pgoff)
91{
92    struct mm_struct *mm = vma->vm_mm;
93    int err;
94
95    do {
96        err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
97        if (err)
98            return err;
99
100        size -= PAGE_SIZE;
101        addr += PAGE_SIZE;
102        pgoff++;
103    } while (size);
104
105    return 0;
106}
107EXPORT_SYMBOL(generic_file_remap_pages);
108
109/**
110 * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
111 * @start: start of the remapped virtual memory range
112 * @size: size of the remapped virtual memory range
113 * @prot: new protection bits of the range (see NOTE)
114 * @pgoff: to-be-mapped page of the backing store file
115 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
116 *
117 * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
118 * (shared backing store file).
119 *
120 * This syscall works purely via pagetables, so it's the most efficient
121 * way to map the same (large) file into a given virtual window. Unlike
122 * mmap()/mremap() it does not create any new vmas. The new mappings are
123 * also safe across swapout.
124 *
125 * NOTE: the @prot parameter right now is ignored (but must be zero),
126 * and the vma's default protection is used. Arbitrary protections
127 * might be implemented in the future.
128 */
129SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
130        unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
131{
132    struct mm_struct *mm = current->mm;
133    struct address_space *mapping;
134    struct vm_area_struct *vma;
135    int err = -EINVAL;
136    int has_write_lock = 0;
137    vm_flags_t vm_flags = 0;
138
139    if (prot)
140        return err;
141    /*
142     * Sanitize the syscall parameters:
143     */
144    start = start & PAGE_MASK;
145    size = size & PAGE_MASK;
146
147    /* Does the address range wrap, or is the span zero-sized? */
148    if (start + size <= start)
149        return err;
150
151    /* Does pgoff wrap? */
152    if (pgoff + (size >> PAGE_SHIFT) < pgoff)
153        return err;
154
155    /* Can we represent this offset inside this architecture's pte's? */
156#if PTE_FILE_MAX_BITS < BITS_PER_LONG
157    if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
158        return err;
159#endif
160
161    /* We need down_write() to change vma->vm_flags. */
162    down_read(&mm->mmap_sem);
163 retry:
164    vma = find_vma(mm, start);
165
166    /*
167     * Make sure the vma is shared, that it supports prefaulting,
168     * and that the remapped range is valid and fully within
169     * the single existing vma.
170     */
171    if (!vma || !(vma->vm_flags & VM_SHARED))
172        goto out;
173
174    if (!vma->vm_ops || !vma->vm_ops->remap_pages)
175        goto out;
176
177    if (start < vma->vm_start || start + size > vma->vm_end)
178        goto out;
179
180    /* Must set VM_NONLINEAR before any pages are populated. */
181    if (!(vma->vm_flags & VM_NONLINEAR)) {
182        /*
183         * vm_private_data is used as a swapout cursor
184         * in a VM_NONLINEAR vma.
185         */
186        if (vma->vm_private_data)
187            goto out;
188
189        /* Don't need a nonlinear mapping, exit success */
190        if (pgoff == linear_page_index(vma, start)) {
191            err = 0;
192            goto out;
193        }
194
195        if (!has_write_lock) {
196get_write_lock:
197            up_read(&mm->mmap_sem);
198            down_write(&mm->mmap_sem);
199            has_write_lock = 1;
200            goto retry;
201        }
202        mapping = vma->vm_file->f_mapping;
203        /*
204         * page_mkclean doesn't work on nonlinear vmas, so if
205         * dirty pages need to be accounted, emulate with linear
206         * vmas.
207         */
208        if (mapping_cap_account_dirty(mapping)) {
209            unsigned long addr;
210            struct file *file = get_file(vma->vm_file);
211
212            addr = mmap_region(file, start, size,
213                    vma->vm_flags, pgoff);
214            fput(file);
215            if (IS_ERR_VALUE(addr)) {
216                err = addr;
217            } else {
218                BUG_ON(addr != start);
219                err = 0;
220            }
221            goto out;
222        }
223        mutex_lock(&mapping->i_mmap_mutex);
224        flush_dcache_mmap_lock(mapping);
225        vma->vm_flags |= VM_NONLINEAR;
226        vma_interval_tree_remove(vma, &mapping->i_mmap);
227        vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
228        flush_dcache_mmap_unlock(mapping);
229        mutex_unlock(&mapping->i_mmap_mutex);
230    }
231
232    if (vma->vm_flags & VM_LOCKED) {
233        /*
234         * drop PG_Mlocked flag for over-mapped range
235         */
236        if (!has_write_lock)
237            goto get_write_lock;
238        vm_flags = vma->vm_flags;
239        munlock_vma_pages_range(vma, start, start + size);
240        vma->vm_flags = vm_flags;
241    }
242
243    mmu_notifier_invalidate_range_start(mm, start, start + size);
244    err = vma->vm_ops->remap_pages(vma, start, size, pgoff);
245    mmu_notifier_invalidate_range_end(mm, start, start + size);
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 (vma)
255        vm_flags = vma->vm_flags;
256    if (likely(!has_write_lock))
257        up_read(&mm->mmap_sem);
258    else
259        up_write(&mm->mmap_sem);
260    if (!err && ((vm_flags & VM_LOCKED) || !(flags & MAP_NONBLOCK)))
261        mm_populate(start, size);
262
263    return err;
264}
265

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