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1 | /* |
2 | * linux/mm/mmu_notifier.c |
3 | * |
4 | * Copyright (C) 2008 Qumranet, Inc. |
5 | * Copyright (C) 2008 SGI |
6 | * Christoph Lameter <clameter@sgi.com> |
7 | * |
8 | * This work is licensed under the terms of the GNU GPL, version 2. See |
9 | * the COPYING file in the top-level directory. |
10 | */ |
11 | |
12 | #include <linux/rculist.h> |
13 | #include <linux/mmu_notifier.h> |
14 | #include <linux/export.h> |
15 | #include <linux/mm.h> |
16 | #include <linux/err.h> |
17 | #include <linux/srcu.h> |
18 | #include <linux/rcupdate.h> |
19 | #include <linux/sched.h> |
20 | #include <linux/slab.h> |
21 | |
22 | /* global SRCU for all MMs */ |
23 | static struct srcu_struct srcu; |
24 | |
25 | /* |
26 | * This function can't run concurrently against mmu_notifier_register |
27 | * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap |
28 | * runs with mm_users == 0. Other tasks may still invoke mmu notifiers |
29 | * in parallel despite there being no task using this mm any more, |
30 | * through the vmas outside of the exit_mmap context, such as with |
31 | * vmtruncate. This serializes against mmu_notifier_unregister with |
32 | * the mmu_notifier_mm->lock in addition to SRCU and it serializes |
33 | * against the other mmu notifiers with SRCU. struct mmu_notifier_mm |
34 | * can't go away from under us as exit_mmap holds an mm_count pin |
35 | * itself. |
36 | */ |
37 | void __mmu_notifier_release(struct mm_struct *mm) |
38 | { |
39 | struct mmu_notifier *mn; |
40 | int id; |
41 | |
42 | /* |
43 | * SRCU here will block mmu_notifier_unregister until |
44 | * ->release returns. |
45 | */ |
46 | id = srcu_read_lock(&srcu); |
47 | hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) |
48 | /* |
49 | * If ->release runs before mmu_notifier_unregister it must be |
50 | * handled, as it's the only way for the driver to flush all |
51 | * existing sptes and stop the driver from establishing any more |
52 | * sptes before all the pages in the mm are freed. |
53 | */ |
54 | if (mn->ops->release) |
55 | mn->ops->release(mn, mm); |
56 | srcu_read_unlock(&srcu, id); |
57 | |
58 | spin_lock(&mm->mmu_notifier_mm->lock); |
59 | while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) { |
60 | mn = hlist_entry(mm->mmu_notifier_mm->list.first, |
61 | struct mmu_notifier, |
62 | hlist); |
63 | /* |
64 | * We arrived before mmu_notifier_unregister so |
65 | * mmu_notifier_unregister will do nothing other than to wait |
66 | * for ->release to finish and for mmu_notifier_unregister to |
67 | * return. |
68 | */ |
69 | hlist_del_init_rcu(&mn->hlist); |
70 | } |
71 | spin_unlock(&mm->mmu_notifier_mm->lock); |
72 | |
73 | /* |
74 | * synchronize_srcu here prevents mmu_notifier_release from returning to |
75 | * exit_mmap (which would proceed with freeing all pages in the mm) |
76 | * until the ->release method returns, if it was invoked by |
77 | * mmu_notifier_unregister. |
78 | * |
79 | * The mmu_notifier_mm can't go away from under us because one mm_count |
80 | * is held by exit_mmap. |
81 | */ |
82 | synchronize_srcu(&srcu); |
83 | } |
84 | |
85 | /* |
86 | * If no young bitflag is supported by the hardware, ->clear_flush_young can |
87 | * unmap the address and return 1 or 0 depending if the mapping previously |
88 | * existed or not. |
89 | */ |
90 | int __mmu_notifier_clear_flush_young(struct mm_struct *mm, |
91 | unsigned long address) |
92 | { |
93 | struct mmu_notifier *mn; |
94 | int young = 0, id; |
95 | |
96 | id = srcu_read_lock(&srcu); |
97 | hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) { |
98 | if (mn->ops->clear_flush_young) |
99 | young |= mn->ops->clear_flush_young(mn, mm, address); |
100 | } |
101 | srcu_read_unlock(&srcu, id); |
102 | |
103 | return young; |
104 | } |
105 | |
106 | int __mmu_notifier_test_young(struct mm_struct *mm, |
107 | unsigned long address) |
108 | { |
109 | struct mmu_notifier *mn; |
110 | int young = 0, id; |
111 | |
112 | id = srcu_read_lock(&srcu); |
113 | hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) { |
114 | if (mn->ops->test_young) { |
115 | young = mn->ops->test_young(mn, mm, address); |
116 | if (young) |
117 | break; |
118 | } |
119 | } |
120 | srcu_read_unlock(&srcu, id); |
121 | |
122 | return young; |
123 | } |
124 | |
125 | void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address, |
126 | pte_t pte) |
127 | { |
128 | struct mmu_notifier *mn; |
129 | int id; |
130 | |
131 | id = srcu_read_lock(&srcu); |
132 | hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) { |
133 | if (mn->ops->change_pte) |
134 | mn->ops->change_pte(mn, mm, address, pte); |
135 | } |
136 | srcu_read_unlock(&srcu, id); |
137 | } |
138 | |
139 | void __mmu_notifier_invalidate_page(struct mm_struct *mm, |
140 | unsigned long address) |
141 | { |
142 | struct mmu_notifier *mn; |
143 | int id; |
144 | |
145 | id = srcu_read_lock(&srcu); |
146 | hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) { |
147 | if (mn->ops->invalidate_page) |
148 | mn->ops->invalidate_page(mn, mm, address); |
149 | } |
150 | srcu_read_unlock(&srcu, id); |
151 | } |
152 | |
153 | void __mmu_notifier_invalidate_range_start(struct mm_struct *mm, |
154 | unsigned long start, unsigned long end) |
155 | { |
156 | struct mmu_notifier *mn; |
157 | int id; |
158 | |
159 | id = srcu_read_lock(&srcu); |
160 | hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) { |
161 | if (mn->ops->invalidate_range_start) |
162 | mn->ops->invalidate_range_start(mn, mm, start, end); |
163 | } |
164 | srcu_read_unlock(&srcu, id); |
165 | } |
166 | EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start); |
167 | |
168 | void __mmu_notifier_invalidate_range_end(struct mm_struct *mm, |
169 | unsigned long start, unsigned long end) |
170 | { |
171 | struct mmu_notifier *mn; |
172 | int id; |
173 | |
174 | id = srcu_read_lock(&srcu); |
175 | hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) { |
176 | if (mn->ops->invalidate_range_end) |
177 | mn->ops->invalidate_range_end(mn, mm, start, end); |
178 | } |
179 | srcu_read_unlock(&srcu, id); |
180 | } |
181 | EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end); |
182 | |
183 | static int do_mmu_notifier_register(struct mmu_notifier *mn, |
184 | struct mm_struct *mm, |
185 | int take_mmap_sem) |
186 | { |
187 | struct mmu_notifier_mm *mmu_notifier_mm; |
188 | int ret; |
189 | |
190 | BUG_ON(atomic_read(&mm->mm_users) <= 0); |
191 | |
192 | /* |
193 | * Verify that mmu_notifier_init() already run and the global srcu is |
194 | * initialized. |
195 | */ |
196 | BUG_ON(!srcu.per_cpu_ref); |
197 | |
198 | ret = -ENOMEM; |
199 | mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL); |
200 | if (unlikely(!mmu_notifier_mm)) |
201 | goto out; |
202 | |
203 | if (take_mmap_sem) |
204 | down_write(&mm->mmap_sem); |
205 | ret = mm_take_all_locks(mm); |
206 | if (unlikely(ret)) |
207 | goto out_clean; |
208 | |
209 | if (!mm_has_notifiers(mm)) { |
210 | INIT_HLIST_HEAD(&mmu_notifier_mm->list); |
211 | spin_lock_init(&mmu_notifier_mm->lock); |
212 | |
213 | mm->mmu_notifier_mm = mmu_notifier_mm; |
214 | mmu_notifier_mm = NULL; |
215 | } |
216 | atomic_inc(&mm->mm_count); |
217 | |
218 | /* |
219 | * Serialize the update against mmu_notifier_unregister. A |
220 | * side note: mmu_notifier_release can't run concurrently with |
221 | * us because we hold the mm_users pin (either implicitly as |
222 | * current->mm or explicitly with get_task_mm() or similar). |
223 | * We can't race against any other mmu notifier method either |
224 | * thanks to mm_take_all_locks(). |
225 | */ |
226 | spin_lock(&mm->mmu_notifier_mm->lock); |
227 | hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list); |
228 | spin_unlock(&mm->mmu_notifier_mm->lock); |
229 | |
230 | mm_drop_all_locks(mm); |
231 | out_clean: |
232 | if (take_mmap_sem) |
233 | up_write(&mm->mmap_sem); |
234 | kfree(mmu_notifier_mm); |
235 | out: |
236 | BUG_ON(atomic_read(&mm->mm_users) <= 0); |
237 | return ret; |
238 | } |
239 | |
240 | /* |
241 | * Must not hold mmap_sem nor any other VM related lock when calling |
242 | * this registration function. Must also ensure mm_users can't go down |
243 | * to zero while this runs to avoid races with mmu_notifier_release, |
244 | * so mm has to be current->mm or the mm should be pinned safely such |
245 | * as with get_task_mm(). If the mm is not current->mm, the mm_users |
246 | * pin should be released by calling mmput after mmu_notifier_register |
247 | * returns. mmu_notifier_unregister must be always called to |
248 | * unregister the notifier. mm_count is automatically pinned to allow |
249 | * mmu_notifier_unregister to safely run at any time later, before or |
250 | * after exit_mmap. ->release will always be called before exit_mmap |
251 | * frees the pages. |
252 | */ |
253 | int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm) |
254 | { |
255 | return do_mmu_notifier_register(mn, mm, 1); |
256 | } |
257 | EXPORT_SYMBOL_GPL(mmu_notifier_register); |
258 | |
259 | /* |
260 | * Same as mmu_notifier_register but here the caller must hold the |
261 | * mmap_sem in write mode. |
262 | */ |
263 | int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm) |
264 | { |
265 | return do_mmu_notifier_register(mn, mm, 0); |
266 | } |
267 | EXPORT_SYMBOL_GPL(__mmu_notifier_register); |
268 | |
269 | /* this is called after the last mmu_notifier_unregister() returned */ |
270 | void __mmu_notifier_mm_destroy(struct mm_struct *mm) |
271 | { |
272 | BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list)); |
273 | kfree(mm->mmu_notifier_mm); |
274 | mm->mmu_notifier_mm = LIST_POISON1; /* debug */ |
275 | } |
276 | |
277 | /* |
278 | * This releases the mm_count pin automatically and frees the mm |
279 | * structure if it was the last user of it. It serializes against |
280 | * running mmu notifiers with SRCU and against mmu_notifier_unregister |
281 | * with the unregister lock + SRCU. All sptes must be dropped before |
282 | * calling mmu_notifier_unregister. ->release or any other notifier |
283 | * method may be invoked concurrently with mmu_notifier_unregister, |
284 | * and only after mmu_notifier_unregister returned we're guaranteed |
285 | * that ->release or any other method can't run anymore. |
286 | */ |
287 | void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm) |
288 | { |
289 | BUG_ON(atomic_read(&mm->mm_count) <= 0); |
290 | |
291 | if (!hlist_unhashed(&mn->hlist)) { |
292 | /* |
293 | * SRCU here will force exit_mmap to wait for ->release to |
294 | * finish before freeing the pages. |
295 | */ |
296 | int id; |
297 | |
298 | id = srcu_read_lock(&srcu); |
299 | /* |
300 | * exit_mmap will block in mmu_notifier_release to guarantee |
301 | * that ->release is called before freeing the pages. |
302 | */ |
303 | if (mn->ops->release) |
304 | mn->ops->release(mn, mm); |
305 | srcu_read_unlock(&srcu, id); |
306 | |
307 | spin_lock(&mm->mmu_notifier_mm->lock); |
308 | /* |
309 | * Can not use list_del_rcu() since __mmu_notifier_release |
310 | * can delete it before we hold the lock. |
311 | */ |
312 | hlist_del_init_rcu(&mn->hlist); |
313 | spin_unlock(&mm->mmu_notifier_mm->lock); |
314 | } |
315 | |
316 | /* |
317 | * Wait for any running method to finish, of course including |
318 | * ->release if it was run by mmu_notifier_release instead of us. |
319 | */ |
320 | synchronize_srcu(&srcu); |
321 | |
322 | BUG_ON(atomic_read(&mm->mm_count) <= 0); |
323 | |
324 | mmdrop(mm); |
325 | } |
326 | EXPORT_SYMBOL_GPL(mmu_notifier_unregister); |
327 | |
328 | static int __init mmu_notifier_init(void) |
329 | { |
330 | return init_srcu_struct(&srcu); |
331 | } |
332 | |
333 | module_init(mmu_notifier_init); |
334 |
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