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