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