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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 */
24 DEFINE_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 */
31 void mmu_notifier_call_srcu(struct rcu_head *rcu,
32 void (*func)(struct rcu_head *rcu))
33 {
34 call_srcu(&srcu, rcu, func);
35 }
36 EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu);
37
38 void mmu_notifier_synchronize(void)
39 {
40 /* Wait for any running method to finish. */
41 srcu_barrier(&srcu);
42 }
43 EXPORT_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 */
57 void __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 */
110 int __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
127 int __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
144 int __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
163 void __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
177 void __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 }
190 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
191
192 void __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 }
222 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
223
224 void __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 }
237 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
238
239 static int do_mmu_notifier_register(struct mmu_notifier *mn,
240 struct mm_struct *mm,
241 int take_mmap_sem)
242 {
243 struct mmu_notifier_mm *mmu_notifier_mm;
244 int ret;
245
246 BUG_ON(atomic_read(&mm->mm_users) <= 0);
247
248 ret = -ENOMEM;
249 mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
250 if (unlikely(!mmu_notifier_mm))
251 goto out;
252
253 if (take_mmap_sem)
254 down_write(&mm->mmap_sem);
255 ret = mm_take_all_locks(mm);
256 if (unlikely(ret))
257 goto out_clean;
258
259 if (!mm_has_notifiers(mm)) {
260 INIT_HLIST_HEAD(&mmu_notifier_mm->list);
261 spin_lock_init(&mmu_notifier_mm->lock);
262
263 mm->mmu_notifier_mm = mmu_notifier_mm;
264 mmu_notifier_mm = NULL;
265 }
266 mmgrab(mm);
267
268 /*
269 * Serialize the update against mmu_notifier_unregister. A
270 * side note: mmu_notifier_release can't run concurrently with
271 * us because we hold the mm_users pin (either implicitly as
272 * current->mm or explicitly with get_task_mm() or similar).
273 * We can't race against any other mmu notifier method either
274 * thanks to mm_take_all_locks().
275 */
276 spin_lock(&mm->mmu_notifier_mm->lock);
277 hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
278 spin_unlock(&mm->mmu_notifier_mm->lock);
279
280 mm_drop_all_locks(mm);
281 out_clean:
282 if (take_mmap_sem)
283 up_write(&mm->mmap_sem);
284 kfree(mmu_notifier_mm);
285 out:
286 BUG_ON(atomic_read(&mm->mm_users) <= 0);
287 return ret;
288 }
289
290 /*
291 * Must not hold mmap_sem nor any other VM related lock when calling
292 * this registration function. Must also ensure mm_users can't go down
293 * to zero while this runs to avoid races with mmu_notifier_release,
294 * so mm has to be current->mm or the mm should be pinned safely such
295 * as with get_task_mm(). If the mm is not current->mm, the mm_users
296 * pin should be released by calling mmput after mmu_notifier_register
297 * returns. mmu_notifier_unregister must be always called to
298 * unregister the notifier. mm_count is automatically pinned to allow
299 * mmu_notifier_unregister to safely run at any time later, before or
300 * after exit_mmap. ->release will always be called before exit_mmap
301 * frees the pages.
302 */
303 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
304 {
305 return do_mmu_notifier_register(mn, mm, 1);
306 }
307 EXPORT_SYMBOL_GPL(mmu_notifier_register);
308
309 /*
310 * Same as mmu_notifier_register but here the caller must hold the
311 * mmap_sem in write mode.
312 */
313 int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
314 {
315 return do_mmu_notifier_register(mn, mm, 0);
316 }
317 EXPORT_SYMBOL_GPL(__mmu_notifier_register);
318
319 /* this is called after the last mmu_notifier_unregister() returned */
320 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
321 {
322 BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
323 kfree(mm->mmu_notifier_mm);
324 mm->mmu_notifier_mm = LIST_POISON1; /* debug */
325 }
326
327 /*
328 * This releases the mm_count pin automatically and frees the mm
329 * structure if it was the last user of it. It serializes against
330 * running mmu notifiers with SRCU and against mmu_notifier_unregister
331 * with the unregister lock + SRCU. All sptes must be dropped before
332 * calling mmu_notifier_unregister. ->release or any other notifier
333 * method may be invoked concurrently with mmu_notifier_unregister,
334 * and only after mmu_notifier_unregister returned we're guaranteed
335 * that ->release or any other method can't run anymore.
336 */
337 void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
338 {
339 BUG_ON(atomic_read(&mm->mm_count) <= 0);
340
341 if (!hlist_unhashed(&mn->hlist)) {
342 /*
343 * SRCU here will force exit_mmap to wait for ->release to
344 * finish before freeing the pages.
345 */
346 int id;
347
348 id = srcu_read_lock(&srcu);
349 /*
350 * exit_mmap will block in mmu_notifier_release to guarantee
351 * that ->release is called before freeing the pages.
352 */
353 if (mn->ops->release)
354 mn->ops->release(mn, mm);
355 srcu_read_unlock(&srcu, id);
356
357 spin_lock(&mm->mmu_notifier_mm->lock);
358 /*
359 * Can not use list_del_rcu() since __mmu_notifier_release
360 * can delete it before we hold the lock.
361 */
362 hlist_del_init_rcu(&mn->hlist);
363 spin_unlock(&mm->mmu_notifier_mm->lock);
364 }
365
366 /*
367 * Wait for any running method to finish, of course including
368 * ->release if it was run by mmu_notifier_release instead of us.
369 */
370 synchronize_srcu(&srcu);
371
372 BUG_ON(atomic_read(&mm->mm_count) <= 0);
373
374 mmdrop(mm);
375 }
376 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
377
378 /*
379 * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
380 */
381 void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
382 struct mm_struct *mm)
383 {
384 spin_lock(&mm->mmu_notifier_mm->lock);
385 /*
386 * Can not use list_del_rcu() since __mmu_notifier_release
387 * can delete it before we hold the lock.
388 */
389 hlist_del_init_rcu(&mn->hlist);
390 spin_unlock(&mm->mmu_notifier_mm->lock);
391
392 BUG_ON(atomic_read(&mm->mm_count) <= 0);
393 mmdrop(mm);
394 }
395 EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);