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Linux/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 <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/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_clear_young(struct mm_struct *mm,
127                                unsigned long start,
128                                unsigned long end)
129 {
130         struct mmu_notifier *mn;
131         int young = 0, id;
132 
133         id = srcu_read_lock(&srcu);
134         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
135                 if (mn->ops->clear_young)
136                         young |= mn->ops->clear_young(mn, mm, start, end);
137         }
138         srcu_read_unlock(&srcu, id);
139 
140         return young;
141 }
142 
143 int __mmu_notifier_test_young(struct mm_struct *mm,
144                               unsigned long address)
145 {
146         struct mmu_notifier *mn;
147         int young = 0, id;
148 
149         id = srcu_read_lock(&srcu);
150         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
151                 if (mn->ops->test_young) {
152                         young = mn->ops->test_young(mn, mm, address);
153                         if (young)
154                                 break;
155                 }
156         }
157         srcu_read_unlock(&srcu, id);
158 
159         return young;
160 }
161 
162 void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
163                                pte_t pte)
164 {
165         struct mmu_notifier *mn;
166         int id;
167 
168         id = srcu_read_lock(&srcu);
169         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
170                 if (mn->ops->change_pte)
171                         mn->ops->change_pte(mn, mm, address, pte);
172         }
173         srcu_read_unlock(&srcu, id);
174 }
175 
176 void __mmu_notifier_invalidate_page(struct mm_struct *mm,
177                                           unsigned long address)
178 {
179         struct mmu_notifier *mn;
180         int id;
181 
182         id = srcu_read_lock(&srcu);
183         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
184                 if (mn->ops->invalidate_page)
185                         mn->ops->invalidate_page(mn, mm, address);
186         }
187         srcu_read_unlock(&srcu, id);
188 }
189 
190 void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
191                                   unsigned long start, unsigned long end)
192 {
193         struct mmu_notifier *mn;
194         int id;
195 
196         id = srcu_read_lock(&srcu);
197         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
198                 if (mn->ops->invalidate_range_start)
199                         mn->ops->invalidate_range_start(mn, mm, start, end);
200         }
201         srcu_read_unlock(&srcu, id);
202 }
203 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
204 
205 void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
206                                   unsigned long start, unsigned long end)
207 {
208         struct mmu_notifier *mn;
209         int id;
210 
211         id = srcu_read_lock(&srcu);
212         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
213                 /*
214                  * Call invalidate_range here too to avoid the need for the
215                  * subsystem of having to register an invalidate_range_end
216                  * call-back when there is invalidate_range already. Usually a
217                  * subsystem registers either invalidate_range_start()/end() or
218                  * invalidate_range(), so this will be no additional overhead
219                  * (besides the pointer check).
220                  */
221                 if (mn->ops->invalidate_range)
222                         mn->ops->invalidate_range(mn, mm, start, end);
223                 if (mn->ops->invalidate_range_end)
224                         mn->ops->invalidate_range_end(mn, mm, start, end);
225         }
226         srcu_read_unlock(&srcu, id);
227 }
228 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
229 
230 void __mmu_notifier_invalidate_range(struct mm_struct *mm,
231                                   unsigned long start, unsigned long end)
232 {
233         struct mmu_notifier *mn;
234         int id;
235 
236         id = srcu_read_lock(&srcu);
237         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
238                 if (mn->ops->invalidate_range)
239                         mn->ops->invalidate_range(mn, mm, start, end);
240         }
241         srcu_read_unlock(&srcu, id);
242 }
243 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
244 
245 static int do_mmu_notifier_register(struct mmu_notifier *mn,
246                                     struct mm_struct *mm,
247                                     int take_mmap_sem)
248 {
249         struct mmu_notifier_mm *mmu_notifier_mm;
250         int ret;
251 
252         BUG_ON(atomic_read(&mm->mm_users) <= 0);
253 
254         /*
255          * Verify that mmu_notifier_init() already run and the global srcu is
256          * initialized.
257          */
258         BUG_ON(!srcu.per_cpu_ref);
259 
260         ret = -ENOMEM;
261         mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
262         if (unlikely(!mmu_notifier_mm))
263                 goto out;
264 
265         if (take_mmap_sem)
266                 down_write(&mm->mmap_sem);
267         ret = mm_take_all_locks(mm);
268         if (unlikely(ret))
269                 goto out_clean;
270 
271         if (!mm_has_notifiers(mm)) {
272                 INIT_HLIST_HEAD(&mmu_notifier_mm->list);
273                 spin_lock_init(&mmu_notifier_mm->lock);
274 
275                 mm->mmu_notifier_mm = mmu_notifier_mm;
276                 mmu_notifier_mm = NULL;
277         }
278         atomic_inc(&mm->mm_count);
279 
280         /*
281          * Serialize the update against mmu_notifier_unregister. A
282          * side note: mmu_notifier_release can't run concurrently with
283          * us because we hold the mm_users pin (either implicitly as
284          * current->mm or explicitly with get_task_mm() or similar).
285          * We can't race against any other mmu notifier method either
286          * thanks to mm_take_all_locks().
287          */
288         spin_lock(&mm->mmu_notifier_mm->lock);
289         hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
290         spin_unlock(&mm->mmu_notifier_mm->lock);
291 
292         mm_drop_all_locks(mm);
293 out_clean:
294         if (take_mmap_sem)
295                 up_write(&mm->mmap_sem);
296         kfree(mmu_notifier_mm);
297 out:
298         BUG_ON(atomic_read(&mm->mm_users) <= 0);
299         return ret;
300 }
301 
302 /*
303  * Must not hold mmap_sem nor any other VM related lock when calling
304  * this registration function. Must also ensure mm_users can't go down
305  * to zero while this runs to avoid races with mmu_notifier_release,
306  * so mm has to be current->mm or the mm should be pinned safely such
307  * as with get_task_mm(). If the mm is not current->mm, the mm_users
308  * pin should be released by calling mmput after mmu_notifier_register
309  * returns. mmu_notifier_unregister must be always called to
310  * unregister the notifier. mm_count is automatically pinned to allow
311  * mmu_notifier_unregister to safely run at any time later, before or
312  * after exit_mmap. ->release will always be called before exit_mmap
313  * frees the pages.
314  */
315 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
316 {
317         return do_mmu_notifier_register(mn, mm, 1);
318 }
319 EXPORT_SYMBOL_GPL(mmu_notifier_register);
320 
321 /*
322  * Same as mmu_notifier_register but here the caller must hold the
323  * mmap_sem in write mode.
324  */
325 int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
326 {
327         return do_mmu_notifier_register(mn, mm, 0);
328 }
329 EXPORT_SYMBOL_GPL(__mmu_notifier_register);
330 
331 /* this is called after the last mmu_notifier_unregister() returned */
332 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
333 {
334         BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
335         kfree(mm->mmu_notifier_mm);
336         mm->mmu_notifier_mm = LIST_POISON1; /* debug */
337 }
338 
339 /*
340  * This releases the mm_count pin automatically and frees the mm
341  * structure if it was the last user of it. It serializes against
342  * running mmu notifiers with SRCU and against mmu_notifier_unregister
343  * with the unregister lock + SRCU. All sptes must be dropped before
344  * calling mmu_notifier_unregister. ->release or any other notifier
345  * method may be invoked concurrently with mmu_notifier_unregister,
346  * and only after mmu_notifier_unregister returned we're guaranteed
347  * that ->release or any other method can't run anymore.
348  */
349 void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
350 {
351         BUG_ON(atomic_read(&mm->mm_count) <= 0);
352 
353         if (!hlist_unhashed(&mn->hlist)) {
354                 /*
355                  * SRCU here will force exit_mmap to wait for ->release to
356                  * finish before freeing the pages.
357                  */
358                 int id;
359 
360                 id = srcu_read_lock(&srcu);
361                 /*
362                  * exit_mmap will block in mmu_notifier_release to guarantee
363                  * that ->release is called before freeing the pages.
364                  */
365                 if (mn->ops->release)
366                         mn->ops->release(mn, mm);
367                 srcu_read_unlock(&srcu, id);
368 
369                 spin_lock(&mm->mmu_notifier_mm->lock);
370                 /*
371                  * Can not use list_del_rcu() since __mmu_notifier_release
372                  * can delete it before we hold the lock.
373                  */
374                 hlist_del_init_rcu(&mn->hlist);
375                 spin_unlock(&mm->mmu_notifier_mm->lock);
376         }
377 
378         /*
379          * Wait for any running method to finish, of course including
380          * ->release if it was run by mmu_notifier_release instead of us.
381          */
382         synchronize_srcu(&srcu);
383 
384         BUG_ON(atomic_read(&mm->mm_count) <= 0);
385 
386         mmdrop(mm);
387 }
388 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
389 
390 /*
391  * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
392  */
393 void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
394                                         struct mm_struct *mm)
395 {
396         spin_lock(&mm->mmu_notifier_mm->lock);
397         /*
398          * Can not use list_del_rcu() since __mmu_notifier_release
399          * can delete it before we hold the lock.
400          */
401         hlist_del_init_rcu(&mn->hlist);
402         spin_unlock(&mm->mmu_notifier_mm->lock);
403 
404         BUG_ON(atomic_read(&mm->mm_count) <= 0);
405         mmdrop(mm);
406 }
407 EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
408 
409 static int __init mmu_notifier_init(void)
410 {
411         return init_srcu_struct(&srcu);
412 }
413 subsys_initcall(mmu_notifier_init);
414 

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