summaryrefslogtreecommitdiffstats
path: root/mm/mmu_notifier.c
blob: 862b60822d9f8c4761448dee6165974da8405ecb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
/*
 *  linux/mm/mmu_notifier.c
 *
 *  Copyright (C) 2008  Qumranet, Inc.
 *  Copyright (C) 2008  SGI
 *             Christoph Lameter <clameter@sgi.com>
 *
 *  This work is licensed under the terms of the GNU GPL, version 2. See
 *  the COPYING file in the top-level directory.
 */

#include <linux/rculist.h>
#include <linux/mmu_notifier.h>
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/err.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/slab.h>

/*
 * This function can't run concurrently against mmu_notifier_register
 * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
 * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
 * in parallel despite there being no task using this mm any more,
 * through the vmas outside of the exit_mmap context, such as with
 * vmtruncate. This serializes against mmu_notifier_unregister with
 * the mmu_notifier_mm->lock in addition to RCU and it serializes
 * against the other mmu notifiers with RCU. struct mmu_notifier_mm
 * can't go away from under us as exit_mmap holds an mm_count pin
 * itself.
 */
void __mmu_notifier_release(struct mm_struct *mm)
{
	struct mmu_notifier *mn;
	struct hlist_node *n;

	/*
	 * RCU here will block mmu_notifier_unregister until
	 * ->release returns.
	 */
	rcu_read_lock();
	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist)
		/*
		 * if ->release runs before mmu_notifier_unregister it
		 * must be handled as it's the only way for the driver
		 * to flush all existing sptes and stop the driver
		 * from establishing any more sptes before all the
		 * pages in the mm are freed.
		 */
		if (mn->ops->release)
			mn->ops->release(mn, mm);
	rcu_read_unlock();

	spin_lock(&mm->mmu_notifier_mm->lock);
	while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
		mn = hlist_entry(mm->mmu_notifier_mm->list.first,
				 struct mmu_notifier,
				 hlist);
		/*
		 * We arrived before mmu_notifier_unregister so
		 * mmu_notifier_unregister will do nothing other than
		 * to wait ->release to finish and
		 * mmu_notifier_unregister to return.
		 */
		hlist_del_init_rcu(&mn->hlist);
	}
	spin_unlock(&mm->mmu_notifier_mm->lock);

	/*
	 * synchronize_rcu here prevents mmu_notifier_release to
	 * return to exit_mmap (which would proceed freeing all pages
	 * in the mm) until the ->release method returns, if it was
	 * invoked by mmu_notifier_unregister.
	 *
	 * The mmu_notifier_mm can't go away from under us because one
	 * mm_count is hold by exit_mmap.
	 */
	synchronize_rcu();
}

/*
 * If no young bitflag is supported by the hardware, ->clear_flush_young can
 * unmap the address and return 1 or 0 depending if the mapping previously
 * existed or not.
 */
int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
					unsigned long address)
{
	struct mmu_notifier *mn;
	struct hlist_node *n;
	int young = 0;

	rcu_read_lock();
	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
		if (mn->ops->clear_flush_young)
			young |= mn->ops->clear_flush_young(mn, mm, address);
	}
	rcu_read_unlock();

	return young;
}

int __mmu_notifier_test_young(struct mm_struct *mm,
			      unsigned long address)
{
	struct mmu_notifier *mn;
	struct hlist_node *n;
	int young = 0;

	rcu_read_lock();
	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
		if (mn->ops->test_young) {
			young = mn->ops->test_young(mn, mm, address);
			if (young)
				break;
		}
	}
	rcu_read_unlock();

	return young;
}

void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
			       pte_t pte)
{
	struct mmu_notifier *mn;
	struct hlist_node *n;

	rcu_read_lock();
	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
		if (mn->ops->change_pte)
			mn->ops->change_pte(mn, mm, address, pte);
		/*
		 * Some drivers don't have change_pte,
		 * so we must call invalidate_page in that case.
		 */
		else if (mn->ops->invalidate_page)
			mn->ops->invalidate_page(mn, mm, address);
	}
	rcu_read_unlock();
}

void __mmu_notifier_invalidate_page(struct mm_struct *mm,
					  unsigned long address)
{
	struct mmu_notifier *mn;
	struct hlist_node *n;

	rcu_read_lock();
	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
		if (mn->ops->invalidate_page)
			mn->ops->invalidate_page(mn, mm, address);
	}
	rcu_read_unlock();
}

void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
				  unsigned long start, unsigned long end)
{
	struct mmu_notifier *mn;
	struct hlist_node *n;

	rcu_read_lock();
	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
		if (mn->ops->invalidate_range_start)
			mn->ops->invalidate_range_start(mn, mm, start, end);
	}
	rcu_read_unlock();
}

void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
				  unsigned long start, unsigned long end)
{
	struct mmu_notifier *mn;
	struct hlist_node *n;

	rcu_read_lock();
	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
		if (mn->ops->invalidate_range_end)
			mn->ops->invalidate_range_end(mn, mm, start, end);
	}
	rcu_read_unlock();
}

static int do_mmu_notifier_register(struct mmu_notifier *mn,
				    struct mm_struct *mm,
				    int take_mmap_sem)
{
	struct mmu_notifier_mm *mmu_notifier_mm;
	int ret;

	BUG_ON(atomic_read(&mm->mm_users) <= 0);

	ret = -ENOMEM;
	mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
	if (unlikely(!mmu_notifier_mm))
		goto out;

	if (take_mmap_sem)
		down_write(&mm->mmap_sem);
	ret = mm_take_all_locks(mm);
	if (unlikely(ret))
		goto out_cleanup;

	if (!mm_has_notifiers(mm)) {
		INIT_HLIST_HEAD(&mmu_notifier_mm->list);
		spin_lock_init(&mmu_notifier_mm->lock);
		mm->mmu_notifier_mm = mmu_notifier_mm;
		mmu_notifier_mm = NULL;
	}
	atomic_inc(&mm->mm_count);

	/*
	 * Serialize the update against mmu_notifier_unregister. A
	 * side note: mmu_notifier_release can't run concurrently with
	 * us because we hold the mm_users pin (either implicitly as
	 * current->mm or explicitly with get_task_mm() or similar).
	 * We can't race against any other mmu notifier method either
	 * thanks to mm_take_all_locks().
	 */
	spin_lock(&mm->mmu_notifier_mm->lock);
	hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
	spin_unlock(&mm->mmu_notifier_mm->lock);

	mm_drop_all_locks(mm);
out_cleanup:
	if (take_mmap_sem)
		up_write(&mm->mmap_sem);
	/* kfree() does nothing if mmu_notifier_mm is NULL */
	kfree(mmu_notifier_mm);
out:
	BUG_ON(atomic_read(&mm->mm_users) <= 0);
	return ret;
}

/*
 * Must not hold mmap_sem nor any other VM related lock when calling
 * this registration function. Must also ensure mm_users can't go down
 * to zero while this runs to avoid races with mmu_notifier_release,
 * so mm has to be current->mm or the mm should be pinned safely such
 * as with get_task_mm(). If the mm is not current->mm, the mm_users
 * pin should be released by calling mmput after mmu_notifier_register
 * returns. mmu_notifier_unregister must be always called to
 * unregister the notifier. mm_count is automatically pinned to allow
 * mmu_notifier_unregister to safely run at any time later, before or
 * after exit_mmap. ->release will always be called before exit_mmap
 * frees the pages.
 */
int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
{
	return do_mmu_notifier_register(mn, mm, 1);
}
EXPORT_SYMBOL_GPL(mmu_notifier_register);

/*
 * Same as mmu_notifier_register but here the caller must hold the
 * mmap_sem in write mode.
 */
int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
{
	return do_mmu_notifier_register(mn, mm, 0);
}
EXPORT_SYMBOL_GPL(__mmu_notifier_register);

/* this is called after the last mmu_notifier_unregister() returned */
void __mmu_notifier_mm_destroy(struct mm_struct *mm)
{
	BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
	kfree(mm->mmu_notifier_mm);
	mm->mmu_notifier_mm = LIST_POISON1; /* debug */
}

/*
 * This releases the mm_count pin automatically and frees the mm
 * structure if it was the last user of it. It serializes against
 * running mmu notifiers with RCU and against mmu_notifier_unregister
 * with the unregister lock + RCU. All sptes must be dropped before
 * calling mmu_notifier_unregister. ->release or any other notifier
 * method may be invoked concurrently with mmu_notifier_unregister,
 * and only after mmu_notifier_unregister returned we're guaranteed
 * that ->release or any other method can't run anymore.
 */
void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
{
	BUG_ON(atomic_read(&mm->mm_count) <= 0);

	if (!hlist_unhashed(&mn->hlist)) {
		/*
		 * RCU here will force exit_mmap to wait ->release to finish
		 * before freeing the pages.
		 */
		rcu_read_lock();

		/*
		 * exit_mmap will block in mmu_notifier_release to
		 * guarantee ->release is called before freeing the
		 * pages.
		 */
		if (mn->ops->release)
			mn->ops->release(mn, mm);
		rcu_read_unlock();

		spin_lock(&mm->mmu_notifier_mm->lock);
		hlist_del_rcu(&mn->hlist);
		spin_unlock(&mm->mmu_notifier_mm->lock);
	}

	/*
	 * Wait any running method to finish, of course including
	 * ->release if it was run by mmu_notifier_relase instead of us.
	 */
	synchronize_rcu();

	BUG_ON(atomic_read(&mm->mm_count) <= 0);

	mmdrop(mm);
}
EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
OpenPOWER on IntegriCloud