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Linux/mm/mmu_notifier.c

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  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 */
 23 static struct srcu_struct srcu;
 24 
 25 /*
 26  * This function allows mmu_notifier::release callback to delay a call to
 27  * a function that will free appropriate resources. The function must be
 28  * quick and must not block.
 29  */
 30 void mmu_notifier_call_srcu(struct rcu_head *rcu,
 31                             void (*func)(struct rcu_head *rcu))
 32 {
 33         call_srcu(&srcu, rcu, func);
 34 }
 35 EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu);
 36 
 37 void mmu_notifier_synchronize(void)
 38 {
 39         /* Wait for any running method to finish. */
 40         srcu_barrier(&srcu);
 41 }
 42 EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
 43 
 44 /*
 45  * This function can't run concurrently against mmu_notifier_register
 46  * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
 47  * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
 48  * in parallel despite there being no task using this mm any more,
 49  * through the vmas outside of the exit_mmap context, such as with
 50  * vmtruncate. This serializes against mmu_notifier_unregister with
 51  * the mmu_notifier_mm->lock in addition to SRCU and it serializes
 52  * against the other mmu notifiers with SRCU. struct mmu_notifier_mm
 53  * can't go away from under us as exit_mmap holds an mm_count pin
 54  * itself.
 55  */
 56 void __mmu_notifier_release(struct mm_struct *mm)
 57 {
 58         struct mmu_notifier *mn;
 59         int id;
 60 
 61         /*
 62          * SRCU here will block mmu_notifier_unregister until
 63          * ->release returns.
 64          */
 65         id = srcu_read_lock(&srcu);
 66         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
 67                 /*
 68                  * If ->release runs before mmu_notifier_unregister it must be
 69                  * handled, as it's the only way for the driver to flush all
 70                  * existing sptes and stop the driver from establishing any more
 71                  * sptes before all the pages in the mm are freed.
 72                  */
 73                 if (mn->ops->release)
 74                         mn->ops->release(mn, mm);
 75 
 76         spin_lock(&mm->mmu_notifier_mm->lock);
 77         while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
 78                 mn = hlist_entry(mm->mmu_notifier_mm->list.first,
 79                                  struct mmu_notifier,
 80                                  hlist);
 81                 /*
 82                  * We arrived before mmu_notifier_unregister so
 83                  * mmu_notifier_unregister will do nothing other than to wait
 84                  * for ->release to finish and for mmu_notifier_unregister to
 85                  * return.
 86                  */
 87                 hlist_del_init_rcu(&mn->hlist);
 88         }
 89         spin_unlock(&mm->mmu_notifier_mm->lock);
 90         srcu_read_unlock(&srcu, id);
 91 
 92         /*
 93          * synchronize_srcu here prevents mmu_notifier_release from returning to
 94          * exit_mmap (which would proceed with freeing all pages in the mm)
 95          * until the ->release method returns, if it was invoked by
 96          * mmu_notifier_unregister.
 97          *
 98          * The mmu_notifier_mm can't go away from under us because one mm_count
 99          * is held by exit_mmap.
100          */
101         synchronize_srcu(&srcu);
102 }
103 
104 /*
105  * If no young bitflag is supported by the hardware, ->clear_flush_young can
106  * unmap the address and return 1 or 0 depending if the mapping previously
107  * existed or not.
108  */
109 int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
110                                         unsigned long start,
111                                         unsigned long end)
112 {
113         struct mmu_notifier *mn;
114         int young = 0, id;
115 
116         id = srcu_read_lock(&srcu);
117         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
118                 if (mn->ops->clear_flush_young)
119                         young |= mn->ops->clear_flush_young(mn, mm, start, end);
120         }
121         srcu_read_unlock(&srcu, id);
122 
123         return young;
124 }
125 
126 int __mmu_notifier_test_young(struct mm_struct *mm,
127                               unsigned long address)
128 {
129         struct mmu_notifier *mn;
130         int young = 0, id;
131 
132         id = srcu_read_lock(&srcu);
133         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
134                 if (mn->ops->test_young) {
135                         young = mn->ops->test_young(mn, mm, address);
136                         if (young)
137                                 break;
138                 }
139         }
140         srcu_read_unlock(&srcu, id);
141 
142         return young;
143 }
144 
145 void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
146                                pte_t pte)
147 {
148         struct mmu_notifier *mn;
149         int id;
150 
151         id = srcu_read_lock(&srcu);
152         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
153                 if (mn->ops->change_pte)
154                         mn->ops->change_pte(mn, mm, address, pte);
155         }
156         srcu_read_unlock(&srcu, id);
157 }
158 
159 void __mmu_notifier_invalidate_page(struct mm_struct *mm,
160                                           unsigned long address)
161 {
162         struct mmu_notifier *mn;
163         int id;
164 
165         id = srcu_read_lock(&srcu);
166         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
167                 if (mn->ops->invalidate_page)
168                         mn->ops->invalidate_page(mn, mm, address);
169         }
170         srcu_read_unlock(&srcu, id);
171 }
172 
173 void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
174                                   unsigned long start, unsigned long end)
175 {
176         struct mmu_notifier *mn;
177         int id;
178 
179         id = srcu_read_lock(&srcu);
180         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
181                 if (mn->ops->invalidate_range_start)
182                         mn->ops->invalidate_range_start(mn, mm, start, end);
183         }
184         srcu_read_unlock(&srcu, id);
185 }
186 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
187 
188 void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
189                                   unsigned long start, unsigned long end)
190 {
191         struct mmu_notifier *mn;
192         int id;
193 
194         id = srcu_read_lock(&srcu);
195         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
196                 /*
197                  * Call invalidate_range here too to avoid the need for the
198                  * subsystem of having to register an invalidate_range_end
199                  * call-back when there is invalidate_range already. Usually a
200                  * subsystem registers either invalidate_range_start()/end() or
201                  * invalidate_range(), so this will be no additional overhead
202                  * (besides the pointer check).
203                  */
204                 if (mn->ops->invalidate_range)
205                         mn->ops->invalidate_range(mn, mm, start, end);
206                 if (mn->ops->invalidate_range_end)
207                         mn->ops->invalidate_range_end(mn, mm, start, end);
208         }
209         srcu_read_unlock(&srcu, id);
210 }
211 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
212 
213 void __mmu_notifier_invalidate_range(struct mm_struct *mm,
214                                   unsigned long start, unsigned long end)
215 {
216         struct mmu_notifier *mn;
217         int id;
218 
219         id = srcu_read_lock(&srcu);
220         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
221                 if (mn->ops->invalidate_range)
222                         mn->ops->invalidate_range(mn, mm, start, end);
223         }
224         srcu_read_unlock(&srcu, id);
225 }
226 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
227 
228 static int do_mmu_notifier_register(struct mmu_notifier *mn,
229                                     struct mm_struct *mm,
230                                     int take_mmap_sem)
231 {
232         struct mmu_notifier_mm *mmu_notifier_mm;
233         int ret;
234 
235         BUG_ON(atomic_read(&mm->mm_users) <= 0);
236 
237         /*
238          * Verify that mmu_notifier_init() already run and the global srcu is
239          * initialized.
240          */
241         BUG_ON(!srcu.per_cpu_ref);
242 
243         ret = -ENOMEM;
244         mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
245         if (unlikely(!mmu_notifier_mm))
246                 goto out;
247 
248         if (take_mmap_sem)
249                 down_write(&mm->mmap_sem);
250         ret = mm_take_all_locks(mm);
251         if (unlikely(ret))
252                 goto out_clean;
253 
254         if (!mm_has_notifiers(mm)) {
255                 INIT_HLIST_HEAD(&mmu_notifier_mm->list);
256                 spin_lock_init(&mmu_notifier_mm->lock);
257 
258                 mm->mmu_notifier_mm = mmu_notifier_mm;
259                 mmu_notifier_mm = NULL;
260         }
261         atomic_inc(&mm->mm_count);
262 
263         /*
264          * Serialize the update against mmu_notifier_unregister. A
265          * side note: mmu_notifier_release can't run concurrently with
266          * us because we hold the mm_users pin (either implicitly as
267          * current->mm or explicitly with get_task_mm() or similar).
268          * We can't race against any other mmu notifier method either
269          * thanks to mm_take_all_locks().
270          */
271         spin_lock(&mm->mmu_notifier_mm->lock);
272         hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
273         spin_unlock(&mm->mmu_notifier_mm->lock);
274 
275         mm_drop_all_locks(mm);
276 out_clean:
277         if (take_mmap_sem)
278                 up_write(&mm->mmap_sem);
279         kfree(mmu_notifier_mm);
280 out:
281         BUG_ON(atomic_read(&mm->mm_users) <= 0);
282         return ret;
283 }
284 
285 /*
286  * Must not hold mmap_sem nor any other VM related lock when calling
287  * this registration function. Must also ensure mm_users can't go down
288  * to zero while this runs to avoid races with mmu_notifier_release,
289  * so mm has to be current->mm or the mm should be pinned safely such
290  * as with get_task_mm(). If the mm is not current->mm, the mm_users
291  * pin should be released by calling mmput after mmu_notifier_register
292  * returns. mmu_notifier_unregister must be always called to
293  * unregister the notifier. mm_count is automatically pinned to allow
294  * mmu_notifier_unregister to safely run at any time later, before or
295  * after exit_mmap. ->release will always be called before exit_mmap
296  * frees the pages.
297  */
298 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
299 {
300         return do_mmu_notifier_register(mn, mm, 1);
301 }
302 EXPORT_SYMBOL_GPL(mmu_notifier_register);
303 
304 /*
305  * Same as mmu_notifier_register but here the caller must hold the
306  * mmap_sem in write mode.
307  */
308 int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
309 {
310         return do_mmu_notifier_register(mn, mm, 0);
311 }
312 EXPORT_SYMBOL_GPL(__mmu_notifier_register);
313 
314 /* this is called after the last mmu_notifier_unregister() returned */
315 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
316 {
317         BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
318         kfree(mm->mmu_notifier_mm);
319         mm->mmu_notifier_mm = LIST_POISON1; /* debug */
320 }
321 
322 /*
323  * This releases the mm_count pin automatically and frees the mm
324  * structure if it was the last user of it. It serializes against
325  * running mmu notifiers with SRCU and against mmu_notifier_unregister
326  * with the unregister lock + SRCU. All sptes must be dropped before
327  * calling mmu_notifier_unregister. ->release or any other notifier
328  * method may be invoked concurrently with mmu_notifier_unregister,
329  * and only after mmu_notifier_unregister returned we're guaranteed
330  * that ->release or any other method can't run anymore.
331  */
332 void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
333 {
334         BUG_ON(atomic_read(&mm->mm_count) <= 0);
335 
336         if (!hlist_unhashed(&mn->hlist)) {
337                 /*
338                  * SRCU here will force exit_mmap to wait for ->release to
339                  * finish before freeing the pages.
340                  */
341                 int id;
342 
343                 id = srcu_read_lock(&srcu);
344                 /*
345                  * exit_mmap will block in mmu_notifier_release to guarantee
346                  * that ->release is called before freeing the pages.
347                  */
348                 if (mn->ops->release)
349                         mn->ops->release(mn, mm);
350                 srcu_read_unlock(&srcu, id);
351 
352                 spin_lock(&mm->mmu_notifier_mm->lock);
353                 /*
354                  * Can not use list_del_rcu() since __mmu_notifier_release
355                  * can delete it before we hold the lock.
356                  */
357                 hlist_del_init_rcu(&mn->hlist);
358                 spin_unlock(&mm->mmu_notifier_mm->lock);
359         }
360 
361         /*
362          * Wait for any running method to finish, of course including
363          * ->release if it was run by mmu_notifier_release instead of us.
364          */
365         synchronize_srcu(&srcu);
366 
367         BUG_ON(atomic_read(&mm->mm_count) <= 0);
368 
369         mmdrop(mm);
370 }
371 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
372 
373 /*
374  * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
375  */
376 void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
377                                         struct mm_struct *mm)
378 {
379         spin_lock(&mm->mmu_notifier_mm->lock);
380         /*
381          * Can not use list_del_rcu() since __mmu_notifier_release
382          * can delete it before we hold the lock.
383          */
384         hlist_del_init_rcu(&mn->hlist);
385         spin_unlock(&mm->mmu_notifier_mm->lock);
386 
387         BUG_ON(atomic_read(&mm->mm_count) <= 0);
388         mmdrop(mm);
389 }
390 EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
391 
392 static int __init mmu_notifier_init(void)
393 {
394         return init_srcu_struct(&srcu);
395 }
396 subsys_initcall(mmu_notifier_init);
397 

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