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/module.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 */
33void __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 */
86int __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
103void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
104                   pte_t pte)
105{
106    struct mmu_notifier *mn;
107    struct hlist_node *n;
108
109    rcu_read_lock();
110    hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
111        if (mn->ops->change_pte)
112            mn->ops->change_pte(mn, mm, address, pte);
113        /*
114         * Some drivers don't have change_pte,
115         * so we must call invalidate_page in that case.
116         */
117        else if (mn->ops->invalidate_page)
118            mn->ops->invalidate_page(mn, mm, address);
119    }
120    rcu_read_unlock();
121}
122
123void __mmu_notifier_invalidate_page(struct mm_struct *mm,
124                      unsigned long address)
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->invalidate_page)
132            mn->ops->invalidate_page(mn, mm, address);
133    }
134    rcu_read_unlock();
135}
136
137void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
138                  unsigned long start, unsigned long end)
139{
140    struct mmu_notifier *mn;
141    struct hlist_node *n;
142
143    rcu_read_lock();
144    hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
145        if (mn->ops->invalidate_range_start)
146            mn->ops->invalidate_range_start(mn, mm, start, end);
147    }
148    rcu_read_unlock();
149}
150
151void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
152                  unsigned long start, unsigned long end)
153{
154    struct mmu_notifier *mn;
155    struct hlist_node *n;
156
157    rcu_read_lock();
158    hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
159        if (mn->ops->invalidate_range_end)
160            mn->ops->invalidate_range_end(mn, mm, start, end);
161    }
162    rcu_read_unlock();
163}
164
165static int do_mmu_notifier_register(struct mmu_notifier *mn,
166                    struct mm_struct *mm,
167                    int take_mmap_sem)
168{
169    struct mmu_notifier_mm *mmu_notifier_mm;
170    int ret;
171
172    BUG_ON(atomic_read(&mm->mm_users) <= 0);
173
174    ret = -ENOMEM;
175    mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
176    if (unlikely(!mmu_notifier_mm))
177        goto out;
178
179    if (take_mmap_sem)
180        down_write(&mm->mmap_sem);
181    ret = mm_take_all_locks(mm);
182    if (unlikely(ret))
183        goto out_cleanup;
184
185    if (!mm_has_notifiers(mm)) {
186        INIT_HLIST_HEAD(&mmu_notifier_mm->list);
187        spin_lock_init(&mmu_notifier_mm->lock);
188        mm->mmu_notifier_mm = mmu_notifier_mm;
189        mmu_notifier_mm = NULL;
190    }
191    atomic_inc(&mm->mm_count);
192
193    /*
194     * Serialize the update against mmu_notifier_unregister. A
195     * side note: mmu_notifier_release can't run concurrently with
196     * us because we hold the mm_users pin (either implicitly as
197     * current->mm or explicitly with get_task_mm() or similar).
198     * We can't race against any other mmu notifier method either
199     * thanks to mm_take_all_locks().
200     */
201    spin_lock(&mm->mmu_notifier_mm->lock);
202    hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
203    spin_unlock(&mm->mmu_notifier_mm->lock);
204
205    mm_drop_all_locks(mm);
206out_cleanup:
207    if (take_mmap_sem)
208        up_write(&mm->mmap_sem);
209    /* kfree() does nothing if mmu_notifier_mm is NULL */
210    kfree(mmu_notifier_mm);
211out:
212    BUG_ON(atomic_read(&mm->mm_users) <= 0);
213    return ret;
214}
215
216/*
217 * Must not hold mmap_sem nor any other VM related lock when calling
218 * this registration function. Must also ensure mm_users can't go down
219 * to zero while this runs to avoid races with mmu_notifier_release,
220 * so mm has to be current->mm or the mm should be pinned safely such
221 * as with get_task_mm(). If the mm is not current->mm, the mm_users
222 * pin should be released by calling mmput after mmu_notifier_register
223 * returns. mmu_notifier_unregister must be always called to
224 * unregister the notifier. mm_count is automatically pinned to allow
225 * mmu_notifier_unregister to safely run at any time later, before or
226 * after exit_mmap. ->release will always be called before exit_mmap
227 * frees the pages.
228 */
229int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
230{
231    return do_mmu_notifier_register(mn, mm, 1);
232}
233EXPORT_SYMBOL_GPL(mmu_notifier_register);
234
235/*
236 * Same as mmu_notifier_register but here the caller must hold the
237 * mmap_sem in write mode.
238 */
239int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
240{
241    return do_mmu_notifier_register(mn, mm, 0);
242}
243EXPORT_SYMBOL_GPL(__mmu_notifier_register);
244
245/* this is called after the last mmu_notifier_unregister() returned */
246void __mmu_notifier_mm_destroy(struct mm_struct *mm)
247{
248    BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
249    kfree(mm->mmu_notifier_mm);
250    mm->mmu_notifier_mm = LIST_POISON1; /* debug */
251}
252
253/*
254 * This releases the mm_count pin automatically and frees the mm
255 * structure if it was the last user of it. It serializes against
256 * running mmu notifiers with RCU and against mmu_notifier_unregister
257 * with the unregister lock + RCU. All sptes must be dropped before
258 * calling mmu_notifier_unregister. ->release or any other notifier
259 * method may be invoked concurrently with mmu_notifier_unregister,
260 * and only after mmu_notifier_unregister returned we're guaranteed
261 * that ->release or any other method can't run anymore.
262 */
263void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
264{
265    BUG_ON(atomic_read(&mm->mm_count) <= 0);
266
267    spin_lock(&mm->mmu_notifier_mm->lock);
268    if (!hlist_unhashed(&mn->hlist)) {
269        hlist_del_rcu(&mn->hlist);
270
271        /*
272         * RCU here will force exit_mmap to wait ->release to finish
273         * before freeing the pages.
274         */
275        rcu_read_lock();
276        spin_unlock(&mm->mmu_notifier_mm->lock);
277        /*
278         * exit_mmap will block in mmu_notifier_release to
279         * guarantee ->release is called before freeing the
280         * pages.
281         */
282        if (mn->ops->release)
283            mn->ops->release(mn, mm);
284        rcu_read_unlock();
285    } else
286        spin_unlock(&mm->mmu_notifier_mm->lock);
287
288    /*
289     * Wait any running method to finish, of course including
290     * ->release if it was run by mmu_notifier_relase instead of us.
291     */
292    synchronize_rcu();
293
294    BUG_ON(atomic_read(&mm->mm_count) <= 0);
295
296    mmdrop(mm);
297}
298EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
299

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