xref: /openbmc/linux/mm/mmu_notifier.c (revision 615c36f5)
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/rcupdate.h>
18 #include <linux/sched.h>
19 #include <linux/slab.h>
20 
21 /*
22  * This function can't run concurrently against mmu_notifier_register
23  * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
24  * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
25  * in parallel despite there being no task using this mm any more,
26  * through the vmas outside of the exit_mmap context, such as with
27  * vmtruncate. This serializes against mmu_notifier_unregister with
28  * the mmu_notifier_mm->lock in addition to RCU and it serializes
29  * against the other mmu notifiers with RCU. struct mmu_notifier_mm
30  * can't go away from under us as exit_mmap holds an mm_count pin
31  * itself.
32  */
33 void __mmu_notifier_release(struct mm_struct *mm)
34 {
35 	struct mmu_notifier *mn;
36 
37 	spin_lock(&mm->mmu_notifier_mm->lock);
38 	while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
39 		mn = hlist_entry(mm->mmu_notifier_mm->list.first,
40 				 struct mmu_notifier,
41 				 hlist);
42 		/*
43 		 * We arrived before mmu_notifier_unregister so
44 		 * mmu_notifier_unregister will do nothing other than
45 		 * to wait ->release to finish and
46 		 * mmu_notifier_unregister to return.
47 		 */
48 		hlist_del_init_rcu(&mn->hlist);
49 		/*
50 		 * RCU here will block mmu_notifier_unregister until
51 		 * ->release returns.
52 		 */
53 		rcu_read_lock();
54 		spin_unlock(&mm->mmu_notifier_mm->lock);
55 		/*
56 		 * if ->release runs before mmu_notifier_unregister it
57 		 * must be handled as it's the only way for the driver
58 		 * to flush all existing sptes and stop the driver
59 		 * from establishing any more sptes before all the
60 		 * pages in the mm are freed.
61 		 */
62 		if (mn->ops->release)
63 			mn->ops->release(mn, mm);
64 		rcu_read_unlock();
65 		spin_lock(&mm->mmu_notifier_mm->lock);
66 	}
67 	spin_unlock(&mm->mmu_notifier_mm->lock);
68 
69 	/*
70 	 * synchronize_rcu here prevents mmu_notifier_release to
71 	 * return to exit_mmap (which would proceed freeing all pages
72 	 * in the mm) until the ->release method returns, if it was
73 	 * invoked by mmu_notifier_unregister.
74 	 *
75 	 * The mmu_notifier_mm can't go away from under us because one
76 	 * mm_count is hold by exit_mmap.
77 	 */
78 	synchronize_rcu();
79 }
80 
81 /*
82  * If no young bitflag is supported by the hardware, ->clear_flush_young can
83  * unmap the address and return 1 or 0 depending if the mapping previously
84  * existed or not.
85  */
86 int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
87 					unsigned long address)
88 {
89 	struct mmu_notifier *mn;
90 	struct hlist_node *n;
91 	int young = 0;
92 
93 	rcu_read_lock();
94 	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
95 		if (mn->ops->clear_flush_young)
96 			young |= mn->ops->clear_flush_young(mn, mm, address);
97 	}
98 	rcu_read_unlock();
99 
100 	return young;
101 }
102 
103 int __mmu_notifier_test_young(struct mm_struct *mm,
104 			      unsigned long address)
105 {
106 	struct mmu_notifier *mn;
107 	struct hlist_node *n;
108 	int young = 0;
109 
110 	rcu_read_lock();
111 	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
112 		if (mn->ops->test_young) {
113 			young = mn->ops->test_young(mn, mm, address);
114 			if (young)
115 				break;
116 		}
117 	}
118 	rcu_read_unlock();
119 
120 	return young;
121 }
122 
123 void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
124 			       pte_t pte)
125 {
126 	struct mmu_notifier *mn;
127 	struct hlist_node *n;
128 
129 	rcu_read_lock();
130 	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
131 		if (mn->ops->change_pte)
132 			mn->ops->change_pte(mn, mm, address, pte);
133 		/*
134 		 * Some drivers don't have change_pte,
135 		 * so we must call invalidate_page in that case.
136 		 */
137 		else if (mn->ops->invalidate_page)
138 			mn->ops->invalidate_page(mn, mm, address);
139 	}
140 	rcu_read_unlock();
141 }
142 
143 void __mmu_notifier_invalidate_page(struct mm_struct *mm,
144 					  unsigned long address)
145 {
146 	struct mmu_notifier *mn;
147 	struct hlist_node *n;
148 
149 	rcu_read_lock();
150 	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
151 		if (mn->ops->invalidate_page)
152 			mn->ops->invalidate_page(mn, mm, address);
153 	}
154 	rcu_read_unlock();
155 }
156 
157 void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
158 				  unsigned long start, unsigned long end)
159 {
160 	struct mmu_notifier *mn;
161 	struct hlist_node *n;
162 
163 	rcu_read_lock();
164 	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
165 		if (mn->ops->invalidate_range_start)
166 			mn->ops->invalidate_range_start(mn, mm, start, end);
167 	}
168 	rcu_read_unlock();
169 }
170 
171 void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
172 				  unsigned long start, unsigned long end)
173 {
174 	struct mmu_notifier *mn;
175 	struct hlist_node *n;
176 
177 	rcu_read_lock();
178 	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
179 		if (mn->ops->invalidate_range_end)
180 			mn->ops->invalidate_range_end(mn, mm, start, end);
181 	}
182 	rcu_read_unlock();
183 }
184 
185 static int do_mmu_notifier_register(struct mmu_notifier *mn,
186 				    struct mm_struct *mm,
187 				    int take_mmap_sem)
188 {
189 	struct mmu_notifier_mm *mmu_notifier_mm;
190 	int ret;
191 
192 	BUG_ON(atomic_read(&mm->mm_users) <= 0);
193 
194 	ret = -ENOMEM;
195 	mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
196 	if (unlikely(!mmu_notifier_mm))
197 		goto out;
198 
199 	if (take_mmap_sem)
200 		down_write(&mm->mmap_sem);
201 	ret = mm_take_all_locks(mm);
202 	if (unlikely(ret))
203 		goto out_cleanup;
204 
205 	if (!mm_has_notifiers(mm)) {
206 		INIT_HLIST_HEAD(&mmu_notifier_mm->list);
207 		spin_lock_init(&mmu_notifier_mm->lock);
208 		mm->mmu_notifier_mm = mmu_notifier_mm;
209 		mmu_notifier_mm = NULL;
210 	}
211 	atomic_inc(&mm->mm_count);
212 
213 	/*
214 	 * Serialize the update against mmu_notifier_unregister. A
215 	 * side note: mmu_notifier_release can't run concurrently with
216 	 * us because we hold the mm_users pin (either implicitly as
217 	 * current->mm or explicitly with get_task_mm() or similar).
218 	 * We can't race against any other mmu notifier method either
219 	 * thanks to mm_take_all_locks().
220 	 */
221 	spin_lock(&mm->mmu_notifier_mm->lock);
222 	hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
223 	spin_unlock(&mm->mmu_notifier_mm->lock);
224 
225 	mm_drop_all_locks(mm);
226 out_cleanup:
227 	if (take_mmap_sem)
228 		up_write(&mm->mmap_sem);
229 	/* kfree() does nothing if mmu_notifier_mm is NULL */
230 	kfree(mmu_notifier_mm);
231 out:
232 	BUG_ON(atomic_read(&mm->mm_users) <= 0);
233 	return ret;
234 }
235 
236 /*
237  * Must not hold mmap_sem nor any other VM related lock when calling
238  * this registration function. Must also ensure mm_users can't go down
239  * to zero while this runs to avoid races with mmu_notifier_release,
240  * so mm has to be current->mm or the mm should be pinned safely such
241  * as with get_task_mm(). If the mm is not current->mm, the mm_users
242  * pin should be released by calling mmput after mmu_notifier_register
243  * returns. mmu_notifier_unregister must be always called to
244  * unregister the notifier. mm_count is automatically pinned to allow
245  * mmu_notifier_unregister to safely run at any time later, before or
246  * after exit_mmap. ->release will always be called before exit_mmap
247  * frees the pages.
248  */
249 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
250 {
251 	return do_mmu_notifier_register(mn, mm, 1);
252 }
253 EXPORT_SYMBOL_GPL(mmu_notifier_register);
254 
255 /*
256  * Same as mmu_notifier_register but here the caller must hold the
257  * mmap_sem in write mode.
258  */
259 int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
260 {
261 	return do_mmu_notifier_register(mn, mm, 0);
262 }
263 EXPORT_SYMBOL_GPL(__mmu_notifier_register);
264 
265 /* this is called after the last mmu_notifier_unregister() returned */
266 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
267 {
268 	BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
269 	kfree(mm->mmu_notifier_mm);
270 	mm->mmu_notifier_mm = LIST_POISON1; /* debug */
271 }
272 
273 /*
274  * This releases the mm_count pin automatically and frees the mm
275  * structure if it was the last user of it. It serializes against
276  * running mmu notifiers with RCU and against mmu_notifier_unregister
277  * with the unregister lock + RCU. All sptes must be dropped before
278  * calling mmu_notifier_unregister. ->release or any other notifier
279  * method may be invoked concurrently with mmu_notifier_unregister,
280  * and only after mmu_notifier_unregister returned we're guaranteed
281  * that ->release or any other method can't run anymore.
282  */
283 void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
284 {
285 	BUG_ON(atomic_read(&mm->mm_count) <= 0);
286 
287 	spin_lock(&mm->mmu_notifier_mm->lock);
288 	if (!hlist_unhashed(&mn->hlist)) {
289 		hlist_del_rcu(&mn->hlist);
290 
291 		/*
292 		 * RCU here will force exit_mmap to wait ->release to finish
293 		 * before freeing the pages.
294 		 */
295 		rcu_read_lock();
296 		spin_unlock(&mm->mmu_notifier_mm->lock);
297 		/*
298 		 * exit_mmap will block in mmu_notifier_release to
299 		 * guarantee ->release is called before freeing the
300 		 * pages.
301 		 */
302 		if (mn->ops->release)
303 			mn->ops->release(mn, mm);
304 		rcu_read_unlock();
305 	} else
306 		spin_unlock(&mm->mmu_notifier_mm->lock);
307 
308 	/*
309 	 * Wait any running method to finish, of course including
310 	 * ->release if it was run by mmu_notifier_relase instead of us.
311 	 */
312 	synchronize_rcu();
313 
314 	BUG_ON(atomic_read(&mm->mm_count) <= 0);
315 
316 	mmdrop(mm);
317 }
318 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
319