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
103int __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
123void __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
143void __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
157void __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
171void __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
185static 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);
226out_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);
231out:
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 */
249int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
250{
251    return do_mmu_notifier_register(mn, mm, 1);
252}
253EXPORT_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 */
259int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
260{
261    return do_mmu_notifier_register(mn, mm, 0);
262}
263EXPORT_SYMBOL_GPL(__mmu_notifier_register);
264
265/* this is called after the last mmu_notifier_unregister() returned */
266void __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 */
283void 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}
318EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
319

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