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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_invalidate_page(struct mm_struct *mm,
103 unsigned long address)
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->invalidate_page)
111 mn->ops->invalidate_page(mn, mm, address);
112 }
113 rcu_read_unlock();
114 }
115
116 void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
117 unsigned long start, unsigned long end)
118 {
119 struct mmu_notifier *mn;
120 struct hlist_node *n;
121
122 rcu_read_lock();
123 hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
124 if (mn->ops->invalidate_range_start)
125 mn->ops->invalidate_range_start(mn, mm, start, end);
126 }
127 rcu_read_unlock();
128 }
129
130 void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
131 unsigned long start, unsigned long end)
132 {
133 struct mmu_notifier *mn;
134 struct hlist_node *n;
135
136 rcu_read_lock();
137 hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
138 if (mn->ops->invalidate_range_end)
139 mn->ops->invalidate_range_end(mn, mm, start, end);
140 }
141 rcu_read_unlock();
142 }
143
144 static int do_mmu_notifier_register(struct mmu_notifier *mn,
145 struct mm_struct *mm,
146 int take_mmap_sem)
147 {
148 struct mmu_notifier_mm *mmu_notifier_mm;
149 int ret;
150
151 BUG_ON(atomic_read(&mm->mm_users) <= 0);
152
153 ret = -ENOMEM;
154 mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
155 if (unlikely(!mmu_notifier_mm))
156 goto out;
157
158 if (take_mmap_sem)
159 down_write(&mm->mmap_sem);
160 ret = mm_take_all_locks(mm);
161 if (unlikely(ret))
162 goto out_cleanup;
163
164 if (!mm_has_notifiers(mm)) {
165 INIT_HLIST_HEAD(&mmu_notifier_mm->list);
166 spin_lock_init(&mmu_notifier_mm->lock);
167 mm->mmu_notifier_mm = mmu_notifier_mm;
168 mmu_notifier_mm = NULL;
169 }
170 atomic_inc(&mm->mm_count);
171
172 /*
173 * Serialize the update against mmu_notifier_unregister. A
174 * side note: mmu_notifier_release can't run concurrently with
175 * us because we hold the mm_users pin (either implicitly as
176 * current->mm or explicitly with get_task_mm() or similar).
177 * We can't race against any other mmu notifier method either
178 * thanks to mm_take_all_locks().
179 */
180 spin_lock(&mm->mmu_notifier_mm->lock);
181 hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
182 spin_unlock(&mm->mmu_notifier_mm->lock);
183
184 mm_drop_all_locks(mm);
185 out_cleanup:
186 if (take_mmap_sem)
187 up_write(&mm->mmap_sem);
188 /* kfree() does nothing if mmu_notifier_mm is NULL */
189 kfree(mmu_notifier_mm);
190 out:
191 BUG_ON(atomic_read(&mm->mm_users) <= 0);
192 return ret;
193 }
194
195 /*
196 * Must not hold mmap_sem nor any other VM related lock when calling
197 * this registration function. Must also ensure mm_users can't go down
198 * to zero while this runs to avoid races with mmu_notifier_release,
199 * so mm has to be current->mm or the mm should be pinned safely such
200 * as with get_task_mm(). If the mm is not current->mm, the mm_users
201 * pin should be released by calling mmput after mmu_notifier_register
202 * returns. mmu_notifier_unregister must be always called to
203 * unregister the notifier. mm_count is automatically pinned to allow
204 * mmu_notifier_unregister to safely run at any time later, before or
205 * after exit_mmap. ->release will always be called before exit_mmap
206 * frees the pages.
207 */
208 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
209 {
210 return do_mmu_notifier_register(mn, mm, 1);
211 }
212 EXPORT_SYMBOL_GPL(mmu_notifier_register);
213
214 /*
215 * Same as mmu_notifier_register but here the caller must hold the
216 * mmap_sem in write mode.
217 */
218 int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
219 {
220 return do_mmu_notifier_register(mn, mm, 0);
221 }
222 EXPORT_SYMBOL_GPL(__mmu_notifier_register);
223
224 /* this is called after the last mmu_notifier_unregister() returned */
225 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
226 {
227 BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
228 kfree(mm->mmu_notifier_mm);
229 mm->mmu_notifier_mm = LIST_POISON1; /* debug */
230 }
231
232 /*
233 * This releases the mm_count pin automatically and frees the mm
234 * structure if it was the last user of it. It serializes against
235 * running mmu notifiers with RCU and against mmu_notifier_unregister
236 * with the unregister lock + RCU. All sptes must be dropped before
237 * calling mmu_notifier_unregister. ->release or any other notifier
238 * method may be invoked concurrently with mmu_notifier_unregister,
239 * and only after mmu_notifier_unregister returned we're guaranteed
240 * that ->release or any other method can't run anymore.
241 */
242 void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
243 {
244 BUG_ON(atomic_read(&mm->mm_count) <= 0);
245
246 spin_lock(&mm->mmu_notifier_mm->lock);
247 if (!hlist_unhashed(&mn->hlist)) {
248 hlist_del_rcu(&mn->hlist);
249
250 /*
251 * RCU here will force exit_mmap to wait ->release to finish
252 * before freeing the pages.
253 */
254 rcu_read_lock();
255 spin_unlock(&mm->mmu_notifier_mm->lock);
256 /*
257 * exit_mmap will block in mmu_notifier_release to
258 * guarantee ->release is called before freeing the
259 * pages.
260 */
261 if (mn->ops->release)
262 mn->ops->release(mn, mm);
263 rcu_read_unlock();
264 } else
265 spin_unlock(&mm->mmu_notifier_mm->lock);
266
267 /*
268 * Wait any running method to finish, of course including
269 * ->release if it was run by mmu_notifier_relase instead of us.
270 */
271 synchronize_rcu();
272
273 BUG_ON(atomic_read(&mm->mm_count) <= 0);
274
275 mmdrop(mm);
276 }
277 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);