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