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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);
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