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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 <cl@linux.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/sched/mm.h>
21#include <linux/slab.h>
22
23/* global SRCU for all MMs */
24DEFINE_STATIC_SRCU(srcu);
25
26/*
27 * This function allows mmu_notifier::release callback to delay a call to
28 * a function that will free appropriate resources. The function must be
29 * quick and must not block.
30 */
31void mmu_notifier_call_srcu(struct rcu_head *rcu,
32 void (*func)(struct rcu_head *rcu))
33{
34 call_srcu(&srcu, rcu, func);
35}
36EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu);
37
38void mmu_notifier_synchronize(void)
39{
40 /* Wait for any running method to finish. */
41 srcu_barrier(&srcu);
42}
43EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
44
45/*
46 * This function can't run concurrently against mmu_notifier_register
47 * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
48 * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
49 * in parallel despite there being no task using this mm any more,
50 * through the vmas outside of the exit_mmap context, such as with
51 * vmtruncate. This serializes against mmu_notifier_unregister with
52 * the mmu_notifier_mm->lock in addition to SRCU and it serializes
53 * against the other mmu notifiers with SRCU. struct mmu_notifier_mm
54 * can't go away from under us as exit_mmap holds an mm_count pin
55 * itself.
56 */
57void __mmu_notifier_release(struct mm_struct *mm)
58{
59 struct mmu_notifier *mn;
60 int id;
61
62 /*
63 * SRCU here will block mmu_notifier_unregister until
64 * ->release returns.
65 */
66 id = srcu_read_lock(&srcu);
67 hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
68 /*
69 * If ->release runs before mmu_notifier_unregister it must be
70 * handled, as it's the only way for the driver to flush all
71 * existing sptes and stop the driver from establishing any more
72 * sptes before all the pages in the mm are freed.
73 */
74 if (mn->ops->release)
75 mn->ops->release(mn, mm);
76
77 spin_lock(&mm->mmu_notifier_mm->lock);
78 while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
79 mn = hlist_entry(mm->mmu_notifier_mm->list.first,
80 struct mmu_notifier,
81 hlist);
82 /*
83 * We arrived before mmu_notifier_unregister so
84 * mmu_notifier_unregister will do nothing other than to wait
85 * for ->release to finish and for mmu_notifier_unregister to
86 * return.
87 */
88 hlist_del_init_rcu(&mn->hlist);
89 }
90 spin_unlock(&mm->mmu_notifier_mm->lock);
91 srcu_read_unlock(&srcu, id);
92
93 /*
94 * synchronize_srcu here prevents mmu_notifier_release from returning to
95 * exit_mmap (which would proceed with freeing all pages in the mm)
96 * until the ->release method returns, if it was invoked by
97 * mmu_notifier_unregister.
98 *
99 * The mmu_notifier_mm can't go away from under us because one mm_count
100 * is held by exit_mmap.
101 */
102 synchronize_srcu(&srcu);
103}
104
105/*
106 * If no young bitflag is supported by the hardware, ->clear_flush_young can
107 * unmap the address and return 1 or 0 depending if the mapping previously
108 * existed or not.
109 */
110int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
111 unsigned long start,
112 unsigned long end)
113{
114 struct mmu_notifier *mn;
115 int young = 0, id;
116
117 id = srcu_read_lock(&srcu);
118 hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
119 if (mn->ops->clear_flush_young)
120 young |= mn->ops->clear_flush_young(mn, mm, start, end);
121 }
122 srcu_read_unlock(&srcu, id);
123
124 return young;
125}
126
127int __mmu_notifier_clear_young(struct mm_struct *mm,
128 unsigned long start,
129 unsigned long end)
130{
131 struct mmu_notifier *mn;
132 int young = 0, id;
133
134 id = srcu_read_lock(&srcu);
135 hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
136 if (mn->ops->clear_young)
137 young |= mn->ops->clear_young(mn, mm, start, end);
138 }
139 srcu_read_unlock(&srcu, id);
140
141 return young;
142}
143
144int __mmu_notifier_test_young(struct mm_struct *mm,
145 unsigned long address)
146{
147 struct mmu_notifier *mn;
148 int young = 0, id;
149
150 id = srcu_read_lock(&srcu);
151 hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
152 if (mn->ops->test_young) {
153 young = mn->ops->test_young(mn, mm, address);
154 if (young)
155 break;
156 }
157 }
158 srcu_read_unlock(&srcu, id);
159
160 return young;
161}
162
163void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
164 pte_t pte)
165{
166 struct mmu_notifier *mn;
167 int id;
168
169 id = srcu_read_lock(&srcu);
170 hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
171 if (mn->ops->change_pte)
172 mn->ops->change_pte(mn, mm, address, pte);
173 }
174 srcu_read_unlock(&srcu, id);
175}
176
177void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
178 unsigned long start, unsigned long end)
179{
180 struct mmu_notifier *mn;
181 int id;
182
183 id = srcu_read_lock(&srcu);
184 hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
185 if (mn->ops->invalidate_range_start)
186 mn->ops->invalidate_range_start(mn, mm, start, end);
187 }
188 srcu_read_unlock(&srcu, id);
189}
190EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
191
192void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
193 unsigned long start,
194 unsigned long end,
195 bool only_end)
196{
197 struct mmu_notifier *mn;
198 int id;
199
200 id = srcu_read_lock(&srcu);
201 hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
202 /*
203 * Call invalidate_range here too to avoid the need for the
204 * subsystem of having to register an invalidate_range_end
205 * call-back when there is invalidate_range already. Usually a
206 * subsystem registers either invalidate_range_start()/end() or
207 * invalidate_range(), so this will be no additional overhead
208 * (besides the pointer check).
209 *
210 * We skip call to invalidate_range() if we know it is safe ie
211 * call site use mmu_notifier_invalidate_range_only_end() which
212 * is safe to do when we know that a call to invalidate_range()
213 * already happen under page table lock.
214 */
215 if (!only_end && mn->ops->invalidate_range)
216 mn->ops->invalidate_range(mn, mm, start, end);
217 if (mn->ops->invalidate_range_end)
218 mn->ops->invalidate_range_end(mn, mm, start, end);
219 }
220 srcu_read_unlock(&srcu, id);
221}
222EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
223
224void __mmu_notifier_invalidate_range(struct mm_struct *mm,
225 unsigned long start, unsigned long end)
226{
227 struct mmu_notifier *mn;
228 int id;
229
230 id = srcu_read_lock(&srcu);
231 hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
232 if (mn->ops->invalidate_range)
233 mn->ops->invalidate_range(mn, mm, start, end);
234 }
235 srcu_read_unlock(&srcu, id);
236}
237EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
238
239/*
240 * Must be called while holding mm->mmap_sem for either read or write.
241 * The result is guaranteed to be valid until mm->mmap_sem is dropped.
242 */
243bool mm_has_blockable_invalidate_notifiers(struct mm_struct *mm)
244{
245 struct mmu_notifier *mn;
246 int id;
247 bool ret = false;
248
249 WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
250
251 if (!mm_has_notifiers(mm))
252 return ret;
253
254 id = srcu_read_lock(&srcu);
255 hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
256 if (!mn->ops->invalidate_range &&
257 !mn->ops->invalidate_range_start &&
258 !mn->ops->invalidate_range_end)
259 continue;
260
261 if (!(mn->ops->flags & MMU_INVALIDATE_DOES_NOT_BLOCK)) {
262 ret = true;
263 break;
264 }
265 }
266 srcu_read_unlock(&srcu, id);
267 return ret;
268}
269
270static int do_mmu_notifier_register(struct mmu_notifier *mn,
271 struct mm_struct *mm,
272 int take_mmap_sem)
273{
274 struct mmu_notifier_mm *mmu_notifier_mm;
275 int ret;
276
277 BUG_ON(atomic_read(&mm->mm_users) <= 0);
278
279 ret = -ENOMEM;
280 mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
281 if (unlikely(!mmu_notifier_mm))
282 goto out;
283
284 if (take_mmap_sem)
285 down_write(&mm->mmap_sem);
286 ret = mm_take_all_locks(mm);
287 if (unlikely(ret))
288 goto out_clean;
289
290 if (!mm_has_notifiers(mm)) {
291 INIT_HLIST_HEAD(&mmu_notifier_mm->list);
292 spin_lock_init(&mmu_notifier_mm->lock);
293
294 mm->mmu_notifier_mm = mmu_notifier_mm;
295 mmu_notifier_mm = NULL;
296 }
297 mmgrab(mm);
298
299 /*
300 * Serialize the update against mmu_notifier_unregister. A
301 * side note: mmu_notifier_release can't run concurrently with
302 * us because we hold the mm_users pin (either implicitly as
303 * current->mm or explicitly with get_task_mm() or similar).
304 * We can't race against any other mmu notifier method either
305 * thanks to mm_take_all_locks().
306 */
307 spin_lock(&mm->mmu_notifier_mm->lock);
308 hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
309 spin_unlock(&mm->mmu_notifier_mm->lock);
310
311 mm_drop_all_locks(mm);
312out_clean:
313 if (take_mmap_sem)
314 up_write(&mm->mmap_sem);
315 kfree(mmu_notifier_mm);
316out:
317 BUG_ON(atomic_read(&mm->mm_users) <= 0);
318 return ret;
319}
320
321/*
322 * Must not hold mmap_sem nor any other VM related lock when calling
323 * this registration function. Must also ensure mm_users can't go down
324 * to zero while this runs to avoid races with mmu_notifier_release,
325 * so mm has to be current->mm or the mm should be pinned safely such
326 * as with get_task_mm(). If the mm is not current->mm, the mm_users
327 * pin should be released by calling mmput after mmu_notifier_register
328 * returns. mmu_notifier_unregister must be always called to
329 * unregister the notifier. mm_count is automatically pinned to allow
330 * mmu_notifier_unregister to safely run at any time later, before or
331 * after exit_mmap. ->release will always be called before exit_mmap
332 * frees the pages.
333 */
334int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
335{
336 return do_mmu_notifier_register(mn, mm, 1);
337}
338EXPORT_SYMBOL_GPL(mmu_notifier_register);
339
340/*
341 * Same as mmu_notifier_register but here the caller must hold the
342 * mmap_sem in write mode.
343 */
344int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
345{
346 return do_mmu_notifier_register(mn, mm, 0);
347}
348EXPORT_SYMBOL_GPL(__mmu_notifier_register);
349
350/* this is called after the last mmu_notifier_unregister() returned */
351void __mmu_notifier_mm_destroy(struct mm_struct *mm)
352{
353 BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
354 kfree(mm->mmu_notifier_mm);
355 mm->mmu_notifier_mm = LIST_POISON1; /* debug */
356}
357
358/*
359 * This releases the mm_count pin automatically and frees the mm
360 * structure if it was the last user of it. It serializes against
361 * running mmu notifiers with SRCU and against mmu_notifier_unregister
362 * with the unregister lock + SRCU. All sptes must be dropped before
363 * calling mmu_notifier_unregister. ->release or any other notifier
364 * method may be invoked concurrently with mmu_notifier_unregister,
365 * and only after mmu_notifier_unregister returned we're guaranteed
366 * that ->release or any other method can't run anymore.
367 */
368void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
369{
370 BUG_ON(atomic_read(&mm->mm_count) <= 0);
371
372 if (!hlist_unhashed(&mn->hlist)) {
373 /*
374 * SRCU here will force exit_mmap to wait for ->release to
375 * finish before freeing the pages.
376 */
377 int id;
378
379 id = srcu_read_lock(&srcu);
380 /*
381 * exit_mmap will block in mmu_notifier_release to guarantee
382 * that ->release is called before freeing the pages.
383 */
384 if (mn->ops->release)
385 mn->ops->release(mn, mm);
386 srcu_read_unlock(&srcu, id);
387
388 spin_lock(&mm->mmu_notifier_mm->lock);
389 /*
390 * Can not use list_del_rcu() since __mmu_notifier_release
391 * can delete it before we hold the lock.
392 */
393 hlist_del_init_rcu(&mn->hlist);
394 spin_unlock(&mm->mmu_notifier_mm->lock);
395 }
396
397 /*
398 * Wait for any running method to finish, of course including
399 * ->release if it was run by mmu_notifier_release instead of us.
400 */
401 synchronize_srcu(&srcu);
402
403 BUG_ON(atomic_read(&mm->mm_count) <= 0);
404
405 mmdrop(mm);
406}
407EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
408
409/*
410 * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
411 */
412void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
413 struct mm_struct *mm)
414{
415 spin_lock(&mm->mmu_notifier_mm->lock);
416 /*
417 * Can not use list_del_rcu() since __mmu_notifier_release
418 * can delete it before we hold the lock.
419 */
420 hlist_del_init_rcu(&mn->hlist);
421 spin_unlock(&mm->mmu_notifier_mm->lock);
422
423 BUG_ON(atomic_read(&mm->mm_count) <= 0);
424 mmdrop(mm);
425}
426EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
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 */
23static 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 */
37void __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 */
90int __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
106int __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
125void __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
139void __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
153void __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}
166EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
167
168void __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}
181EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
182
183static 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);
231out_clean:
232 if (take_mmap_sem)
233 up_write(&mm->mmap_sem);
234 kfree(mmu_notifier_mm);
235out:
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 */
253int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
254{
255 return do_mmu_notifier_register(mn, mm, 1);
256}
257EXPORT_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 */
263int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
264{
265 return do_mmu_notifier_register(mn, mm, 0);
266}
267EXPORT_SYMBOL_GPL(__mmu_notifier_register);
268
269/* this is called after the last mmu_notifier_unregister() returned */
270void __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 */
287void 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}
326EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
327
328static int __init mmu_notifier_init(void)
329{
330 return init_srcu_struct(&srcu);
331}
332subsys_initcall(mmu_notifier_init);