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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 <cl@linux.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/sched/mm.h>
 21 #include <linux/slab.h>
 22 
 23 /* global SRCU for all MMs */
 24 DEFINE_STATIC_SRCU(srcu);
 25 
 26 /*
 27  * This function allows mmu_notifier::release callback to delay a call to
 28  * a function that will free appropriate resources. The function must be
 29  * quick and must not block.
 30  */
 31 void mmu_notifier_call_srcu(struct rcu_head *rcu,
 32                             void (*func)(struct rcu_head *rcu))
 33 {
 34         call_srcu(&srcu, rcu, func);
 35 }
 36 EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu);
 37 
 38 void mmu_notifier_synchronize(void)
 39 {
 40         /* Wait for any running method to finish. */
 41         srcu_barrier(&srcu);
 42 }
 43 EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
 44 
 45 /*
 46  * This function can't run concurrently against mmu_notifier_register
 47  * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
 48  * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
 49  * in parallel despite there being no task using this mm any more,
 50  * through the vmas outside of the exit_mmap context, such as with
 51  * vmtruncate. This serializes against mmu_notifier_unregister with
 52  * the mmu_notifier_mm->lock in addition to SRCU and it serializes
 53  * against the other mmu notifiers with SRCU. struct mmu_notifier_mm
 54  * can't go away from under us as exit_mmap holds an mm_count pin
 55  * itself.
 56  */
 57 void __mmu_notifier_release(struct mm_struct *mm)
 58 {
 59         struct mmu_notifier *mn;
 60         int id;
 61 
 62         /*
 63          * SRCU here will block mmu_notifier_unregister until
 64          * ->release returns.
 65          */
 66         id = srcu_read_lock(&srcu);
 67         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
 68                 /*
 69                  * If ->release runs before mmu_notifier_unregister it must be
 70                  * handled, as it's the only way for the driver to flush all
 71                  * existing sptes and stop the driver from establishing any more
 72                  * sptes before all the pages in the mm are freed.
 73                  */
 74                 if (mn->ops->release)
 75                         mn->ops->release(mn, mm);
 76 
 77         spin_lock(&mm->mmu_notifier_mm->lock);
 78         while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
 79                 mn = hlist_entry(mm->mmu_notifier_mm->list.first,
 80                                  struct mmu_notifier,
 81                                  hlist);
 82                 /*
 83                  * We arrived before mmu_notifier_unregister so
 84                  * mmu_notifier_unregister will do nothing other than to wait
 85                  * for ->release to finish and for mmu_notifier_unregister to
 86                  * return.
 87                  */
 88                 hlist_del_init_rcu(&mn->hlist);
 89         }
 90         spin_unlock(&mm->mmu_notifier_mm->lock);
 91         srcu_read_unlock(&srcu, id);
 92 
 93         /*
 94          * synchronize_srcu here prevents mmu_notifier_release from returning to
 95          * exit_mmap (which would proceed with freeing all pages in the mm)
 96          * until the ->release method returns, if it was invoked by
 97          * mmu_notifier_unregister.
 98          *
 99          * The mmu_notifier_mm can't go away from under us because one mm_count
100          * is held by exit_mmap.
101          */
102         synchronize_srcu(&srcu);
103 }
104 
105 /*
106  * If no young bitflag is supported by the hardware, ->clear_flush_young can
107  * unmap the address and return 1 or 0 depending if the mapping previously
108  * existed or not.
109  */
110 int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
111                                         unsigned long start,
112                                         unsigned long end)
113 {
114         struct mmu_notifier *mn;
115         int young = 0, id;
116 
117         id = srcu_read_lock(&srcu);
118         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
119                 if (mn->ops->clear_flush_young)
120                         young |= mn->ops->clear_flush_young(mn, mm, start, end);
121         }
122         srcu_read_unlock(&srcu, id);
123 
124         return young;
125 }
126 
127 int __mmu_notifier_clear_young(struct mm_struct *mm,
128                                unsigned long start,
129                                unsigned long end)
130 {
131         struct mmu_notifier *mn;
132         int young = 0, id;
133 
134         id = srcu_read_lock(&srcu);
135         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
136                 if (mn->ops->clear_young)
137                         young |= mn->ops->clear_young(mn, mm, start, end);
138         }
139         srcu_read_unlock(&srcu, id);
140 
141         return young;
142 }
143 
144 int __mmu_notifier_test_young(struct mm_struct *mm,
145                               unsigned long address)
146 {
147         struct mmu_notifier *mn;
148         int young = 0, id;
149 
150         id = srcu_read_lock(&srcu);
151         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
152                 if (mn->ops->test_young) {
153                         young = mn->ops->test_young(mn, mm, address);
154                         if (young)
155                                 break;
156                 }
157         }
158         srcu_read_unlock(&srcu, id);
159 
160         return young;
161 }
162 
163 void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
164                                pte_t pte)
165 {
166         struct mmu_notifier *mn;
167         int id;
168 
169         id = srcu_read_lock(&srcu);
170         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
171                 if (mn->ops->change_pte)
172                         mn->ops->change_pte(mn, mm, address, pte);
173         }
174         srcu_read_unlock(&srcu, id);
175 }
176 
177 void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
178                                   unsigned long start, unsigned long end)
179 {
180         struct mmu_notifier *mn;
181         int id;
182 
183         id = srcu_read_lock(&srcu);
184         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
185                 if (mn->ops->invalidate_range_start)
186                         mn->ops->invalidate_range_start(mn, mm, start, end);
187         }
188         srcu_read_unlock(&srcu, id);
189 }
190 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
191 
192 void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
193                                          unsigned long start,
194                                          unsigned long end,
195                                          bool only_end)
196 {
197         struct mmu_notifier *mn;
198         int id;
199 
200         id = srcu_read_lock(&srcu);
201         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
202                 /*
203                  * Call invalidate_range here too to avoid the need for the
204                  * subsystem of having to register an invalidate_range_end
205                  * call-back when there is invalidate_range already. Usually a
206                  * subsystem registers either invalidate_range_start()/end() or
207                  * invalidate_range(), so this will be no additional overhead
208                  * (besides the pointer check).
209                  *
210                  * We skip call to invalidate_range() if we know it is safe ie
211                  * call site use mmu_notifier_invalidate_range_only_end() which
212                  * is safe to do when we know that a call to invalidate_range()
213                  * already happen under page table lock.
214                  */
215                 if (!only_end && mn->ops->invalidate_range)
216                         mn->ops->invalidate_range(mn, mm, start, end);
217                 if (mn->ops->invalidate_range_end)
218                         mn->ops->invalidate_range_end(mn, mm, start, end);
219         }
220         srcu_read_unlock(&srcu, id);
221 }
222 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
223 
224 void __mmu_notifier_invalidate_range(struct mm_struct *mm,
225                                   unsigned long start, unsigned long end)
226 {
227         struct mmu_notifier *mn;
228         int id;
229 
230         id = srcu_read_lock(&srcu);
231         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
232                 if (mn->ops->invalidate_range)
233                         mn->ops->invalidate_range(mn, mm, start, end);
234         }
235         srcu_read_unlock(&srcu, id);
236 }
237 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
238 
239 static int do_mmu_notifier_register(struct mmu_notifier *mn,
240                                     struct mm_struct *mm,
241                                     int take_mmap_sem)
242 {
243         struct mmu_notifier_mm *mmu_notifier_mm;
244         int ret;
245 
246         BUG_ON(atomic_read(&mm->mm_users) <= 0);
247 
248         ret = -ENOMEM;
249         mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
250         if (unlikely(!mmu_notifier_mm))
251                 goto out;
252 
253         if (take_mmap_sem)
254                 down_write(&mm->mmap_sem);
255         ret = mm_take_all_locks(mm);
256         if (unlikely(ret))
257                 goto out_clean;
258 
259         if (!mm_has_notifiers(mm)) {
260                 INIT_HLIST_HEAD(&mmu_notifier_mm->list);
261                 spin_lock_init(&mmu_notifier_mm->lock);
262 
263                 mm->mmu_notifier_mm = mmu_notifier_mm;
264                 mmu_notifier_mm = NULL;
265         }
266         mmgrab(mm);
267 
268         /*
269          * Serialize the update against mmu_notifier_unregister. A
270          * side note: mmu_notifier_release can't run concurrently with
271          * us because we hold the mm_users pin (either implicitly as
272          * current->mm or explicitly with get_task_mm() or similar).
273          * We can't race against any other mmu notifier method either
274          * thanks to mm_take_all_locks().
275          */
276         spin_lock(&mm->mmu_notifier_mm->lock);
277         hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
278         spin_unlock(&mm->mmu_notifier_mm->lock);
279 
280         mm_drop_all_locks(mm);
281 out_clean:
282         if (take_mmap_sem)
283                 up_write(&mm->mmap_sem);
284         kfree(mmu_notifier_mm);
285 out:
286         BUG_ON(atomic_read(&mm->mm_users) <= 0);
287         return ret;
288 }
289 
290 /*
291  * Must not hold mmap_sem nor any other VM related lock when calling
292  * this registration function. Must also ensure mm_users can't go down
293  * to zero while this runs to avoid races with mmu_notifier_release,
294  * so mm has to be current->mm or the mm should be pinned safely such
295  * as with get_task_mm(). If the mm is not current->mm, the mm_users
296  * pin should be released by calling mmput after mmu_notifier_register
297  * returns. mmu_notifier_unregister must be always called to
298  * unregister the notifier. mm_count is automatically pinned to allow
299  * mmu_notifier_unregister to safely run at any time later, before or
300  * after exit_mmap. ->release will always be called before exit_mmap
301  * frees the pages.
302  */
303 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
304 {
305         return do_mmu_notifier_register(mn, mm, 1);
306 }
307 EXPORT_SYMBOL_GPL(mmu_notifier_register);
308 
309 /*
310  * Same as mmu_notifier_register but here the caller must hold the
311  * mmap_sem in write mode.
312  */
313 int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
314 {
315         return do_mmu_notifier_register(mn, mm, 0);
316 }
317 EXPORT_SYMBOL_GPL(__mmu_notifier_register);
318 
319 /* this is called after the last mmu_notifier_unregister() returned */
320 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
321 {
322         BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
323         kfree(mm->mmu_notifier_mm);
324         mm->mmu_notifier_mm = LIST_POISON1; /* debug */
325 }
326 
327 /*
328  * This releases the mm_count pin automatically and frees the mm
329  * structure if it was the last user of it. It serializes against
330  * running mmu notifiers with SRCU and against mmu_notifier_unregister
331  * with the unregister lock + SRCU. All sptes must be dropped before
332  * calling mmu_notifier_unregister. ->release or any other notifier
333  * method may be invoked concurrently with mmu_notifier_unregister,
334  * and only after mmu_notifier_unregister returned we're guaranteed
335  * that ->release or any other method can't run anymore.
336  */
337 void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
338 {
339         BUG_ON(atomic_read(&mm->mm_count) <= 0);
340 
341         if (!hlist_unhashed(&mn->hlist)) {
342                 /*
343                  * SRCU here will force exit_mmap to wait for ->release to
344                  * finish before freeing the pages.
345                  */
346                 int id;
347 
348                 id = srcu_read_lock(&srcu);
349                 /*
350                  * exit_mmap will block in mmu_notifier_release to guarantee
351                  * that ->release is called before freeing the pages.
352                  */
353                 if (mn->ops->release)
354                         mn->ops->release(mn, mm);
355                 srcu_read_unlock(&srcu, id);
356 
357                 spin_lock(&mm->mmu_notifier_mm->lock);
358                 /*
359                  * Can not use list_del_rcu() since __mmu_notifier_release
360                  * can delete it before we hold the lock.
361                  */
362                 hlist_del_init_rcu(&mn->hlist);
363                 spin_unlock(&mm->mmu_notifier_mm->lock);
364         }
365 
366         /*
367          * Wait for any running method to finish, of course including
368          * ->release if it was run by mmu_notifier_release instead of us.
369          */
370         synchronize_srcu(&srcu);
371 
372         BUG_ON(atomic_read(&mm->mm_count) <= 0);
373 
374         mmdrop(mm);
375 }
376 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
377 
378 /*
379  * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
380  */
381 void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
382                                         struct mm_struct *mm)
383 {
384         spin_lock(&mm->mmu_notifier_mm->lock);
385         /*
386          * Can not use list_del_rcu() since __mmu_notifier_release
387          * can delete it before we hold the lock.
388          */
389         hlist_del_init_rcu(&mn->hlist);
390         spin_unlock(&mm->mmu_notifier_mm->lock);
391 
392         BUG_ON(atomic_read(&mm->mm_count) <= 0);
393         mmdrop(mm);
394 }
395 EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
396 

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