Root/mm/mmu_notifier.c

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}
332
333module_init(mmu_notifier_init);
334

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