tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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
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 /* Does pgoff wrap? */
146 if (pgoff + (size >> PAGE_SHIFT) < pgoff)
147 return err;
148
149 /* Can we represent this offset inside this architecture's pte's? */
150#if PTE_FILE_MAX_BITS < BITS_PER_LONG
151 if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
152 return err;
153#endif
154
155 /* We need down_write() to change vma->vm_flags. */
156 down_read(&mm->mmap_sem);
157 retry:
158 vma = find_vma(mm, start);
159
160 /*
161 * Make sure the vma is shared, that it supports prefaulting,
162 * and that the remapped range is valid and fully within
163 * the single existing vma. vm_private_data is used as a
164 * swapout cursor in a VM_NONLINEAR vma.
165 */
166 if (!vma || !(vma->vm_flags & VM_SHARED))
167 goto out;
168
169 if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))
170 goto out;
171
172 if (!vma->vm_ops || !vma->vm_ops->remap_pages)
173 goto out;
174
175 if (start < vma->vm_start || start + size > vma->vm_end)
176 goto out;
177
178 /* Must set VM_NONLINEAR before any pages are populated. */
179 if (!(vma->vm_flags & VM_NONLINEAR)) {
180 /* Don't need a nonlinear mapping, exit success */
181 if (pgoff == linear_page_index(vma, start)) {
182 err = 0;
183 goto out;
184 }
185
186 if (!has_write_lock) {
187 up_read(&mm->mmap_sem);
188 down_write(&mm->mmap_sem);
189 has_write_lock = 1;
190 goto retry;
191 }
192 mapping = vma->vm_file->f_mapping;
193 /*
194 * page_mkclean doesn't work on nonlinear vmas, so if
195 * dirty pages need to be accounted, emulate with linear
196 * vmas.
197 */
198 if (mapping_cap_account_dirty(mapping)) {
199 unsigned long addr;
200 struct file *file = get_file(vma->vm_file);
201
202 flags &= MAP_NONBLOCK;
203 addr = mmap_region(file, start, size,
204 flags, vma->vm_flags, pgoff);
205 fput(file);
206 if (IS_ERR_VALUE(addr)) {
207 err = addr;
208 } else {
209 BUG_ON(addr != start);
210 err = 0;
211 }
212 goto out;
213 }
214 mutex_lock(&mapping->i_mmap_mutex);
215 flush_dcache_mmap_lock(mapping);
216 vma->vm_flags |= VM_NONLINEAR;
217 vma_interval_tree_remove(vma, &mapping->i_mmap);
218 vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
219 flush_dcache_mmap_unlock(mapping);
220 mutex_unlock(&mapping->i_mmap_mutex);
221 }
222
223 if (vma->vm_flags & VM_LOCKED) {
224 /*
225 * drop PG_Mlocked flag for over-mapped range
226 */
227 vm_flags_t saved_flags = vma->vm_flags;
228 munlock_vma_pages_range(vma, start, start + size);
229 vma->vm_flags = saved_flags;
230 }
231
232 mmu_notifier_invalidate_range_start(mm, start, start + size);
233 err = vma->vm_ops->remap_pages(vma, start, size, pgoff);
234 mmu_notifier_invalidate_range_end(mm, start, start + size);
235 if (!err && !(flags & MAP_NONBLOCK)) {
236 if (vma->vm_flags & VM_LOCKED) {
237 /*
238 * might be mapping previously unmapped range of file
239 */
240 mlock_vma_pages_range(vma, start, start + size);
241 } else {
242 if (unlikely(has_write_lock)) {
243 downgrade_write(&mm->mmap_sem);
244 has_write_lock = 0;
245 }
246 make_pages_present(start, start+size);
247 }
248 }
249
250 /*
251 * We can't clear VM_NONLINEAR because we'd have to do
252 * it after ->populate completes, and that would prevent
253 * downgrading the lock. (Locks can't be upgraded).
254 */
255
256out:
257 if (likely(!has_write_lock))
258 up_read(&mm->mmap_sem);
259 else
260 up_write(&mm->mmap_sem);
261
262 return err;
263}