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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 /*
 39  * This function can't run concurrently against mmu_notifier_register
 40  * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
 41  * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
 42  * in parallel despite there being no task using this mm any more,
 43  * through the vmas outside of the exit_mmap context, such as with
 44  * vmtruncate. This serializes against mmu_notifier_unregister with
 45  * the mmu_notifier_mm->lock in addition to SRCU and it serializes
 46  * against the other mmu notifiers with SRCU. struct mmu_notifier_mm
 47  * can't go away from under us as exit_mmap holds an mm_count pin
 48  * itself.
 49  */
 50 void __mmu_notifier_release(struct mm_struct *mm)
 51 {
 52         struct mmu_notifier *mn;
 53         int id;
 54 
 55         /*
 56          * SRCU here will block mmu_notifier_unregister until
 57          * ->release returns.
 58          */
 59         id = srcu_read_lock(&srcu);
 60         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
 61                 /*
 62                  * If ->release runs before mmu_notifier_unregister it must be
 63                  * handled, as it's the only way for the driver to flush all
 64                  * existing sptes and stop the driver from establishing any more
 65                  * sptes before all the pages in the mm are freed.
 66                  */
 67                 if (mn->ops->release)
 68                         mn->ops->release(mn, mm);
 69 
 70         spin_lock(&mm->mmu_notifier_mm->lock);
 71         while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
 72                 mn = hlist_entry(mm->mmu_notifier_mm->list.first,
 73                                  struct mmu_notifier,
 74                                  hlist);
 75                 /*
 76                  * We arrived before mmu_notifier_unregister so
 77                  * mmu_notifier_unregister will do nothing other than to wait
 78                  * for ->release to finish and for mmu_notifier_unregister to
 79                  * return.
 80                  */
 81                 hlist_del_init_rcu(&mn->hlist);
 82         }
 83         spin_unlock(&mm->mmu_notifier_mm->lock);
 84         srcu_read_unlock(&srcu, id);
 85 
 86         /*
 87          * synchronize_srcu here prevents mmu_notifier_release from returning to
 88          * exit_mmap (which would proceed with freeing all pages in the mm)
 89          * until the ->release method returns, if it was invoked by
 90          * mmu_notifier_unregister.
 91          *
 92          * The mmu_notifier_mm can't go away from under us because one mm_count
 93          * is held by exit_mmap.
 94          */
 95         synchronize_srcu(&srcu);
 96 }
 97 
 98 /*
 99  * If no young bitflag is supported by the hardware, ->clear_flush_young can
100  * unmap the address and return 1 or 0 depending if the mapping previously
101  * existed or not.
102  */
103 int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
104                                         unsigned long start,
105                                         unsigned long end)
106 {
107         struct mmu_notifier *mn;
108         int young = 0, id;
109 
110         id = srcu_read_lock(&srcu);
111         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
112                 if (mn->ops->clear_flush_young)
113                         young |= mn->ops->clear_flush_young(mn, mm, start, end);
114         }
115         srcu_read_unlock(&srcu, id);
116 
117         return young;
118 }
119 
120 int __mmu_notifier_clear_young(struct mm_struct *mm,
121                                unsigned long start,
122                                unsigned long end)
123 {
124         struct mmu_notifier *mn;
125         int young = 0, id;
126 
127         id = srcu_read_lock(&srcu);
128         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
129                 if (mn->ops->clear_young)
130                         young |= mn->ops->clear_young(mn, mm, start, end);
131         }
132         srcu_read_unlock(&srcu, id);
133 
134         return young;
135 }
136 
137 int __mmu_notifier_test_young(struct mm_struct *mm,
138                               unsigned long address)
139 {
140         struct mmu_notifier *mn;
141         int young = 0, id;
142 
143         id = srcu_read_lock(&srcu);
144         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
145                 if (mn->ops->test_young) {
146                         young = mn->ops->test_young(mn, mm, address);
147                         if (young)
148                                 break;
149                 }
150         }
151         srcu_read_unlock(&srcu, id);
152 
153         return young;
154 }
155 
156 void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
157                                pte_t pte)
158 {
159         struct mmu_notifier *mn;
160         int id;
161 
162         id = srcu_read_lock(&srcu);
163         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
164                 if (mn->ops->change_pte)
165                         mn->ops->change_pte(mn, mm, address, pte);
166         }
167         srcu_read_unlock(&srcu, id);
168 }
169 
170 int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
171 {
172         struct mmu_notifier *mn;
173         int ret = 0;
174         int id;
175 
176         id = srcu_read_lock(&srcu);
177         hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {
178                 if (mn->ops->invalidate_range_start) {
179                         int _ret = mn->ops->invalidate_range_start(mn, range);
180                         if (_ret) {
181                                 pr_info("%pS callback failed with %d in %sblockable context.\n",
182                                         mn->ops->invalidate_range_start, _ret,
183                                         !range->blockable ? "non-" : "");
184                                 ret = _ret;
185                         }
186                 }
187         }
188         srcu_read_unlock(&srcu, id);
189 
190         return ret;
191 }
192 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
193 
194 void __mmu_notifier_invalidate_range_end(struct mmu_notifier_range *range,
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, &range->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, range->mm,
217                                                   range->start,
218                                                   range->end);
219                 if (mn->ops->invalidate_range_end)
220                         mn->ops->invalidate_range_end(mn, range);
221         }
222         srcu_read_unlock(&srcu, id);
223 }
224 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
225 
226 void __mmu_notifier_invalidate_range(struct mm_struct *mm,
227                                   unsigned long start, unsigned long end)
228 {
229         struct mmu_notifier *mn;
230         int id;
231 
232         id = srcu_read_lock(&srcu);
233         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
234                 if (mn->ops->invalidate_range)
235                         mn->ops->invalidate_range(mn, mm, start, end);
236         }
237         srcu_read_unlock(&srcu, id);
238 }
239 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
240 
241 static int do_mmu_notifier_register(struct mmu_notifier *mn,
242                                     struct mm_struct *mm,
243                                     int take_mmap_sem)
244 {
245         struct mmu_notifier_mm *mmu_notifier_mm;
246         int ret;
247 
248         BUG_ON(atomic_read(&mm->mm_users) <= 0);
249 
250         ret = -ENOMEM;
251         mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
252         if (unlikely(!mmu_notifier_mm))
253                 goto out;
254 
255         if (take_mmap_sem)
256                 down_write(&mm->mmap_sem);
257         ret = mm_take_all_locks(mm);
258         if (unlikely(ret))
259                 goto out_clean;
260 
261         if (!mm_has_notifiers(mm)) {
262                 INIT_HLIST_HEAD(&mmu_notifier_mm->list);
263                 spin_lock_init(&mmu_notifier_mm->lock);
264 
265                 mm->mmu_notifier_mm = mmu_notifier_mm;
266                 mmu_notifier_mm = NULL;
267         }
268         mmgrab(mm);
269 
270         /*
271          * Serialize the update against mmu_notifier_unregister. A
272          * side note: mmu_notifier_release can't run concurrently with
273          * us because we hold the mm_users pin (either implicitly as
274          * current->mm or explicitly with get_task_mm() or similar).
275          * We can't race against any other mmu notifier method either
276          * thanks to mm_take_all_locks().
277          */
278         spin_lock(&mm->mmu_notifier_mm->lock);
279         hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
280         spin_unlock(&mm->mmu_notifier_mm->lock);
281 
282         mm_drop_all_locks(mm);
283 out_clean:
284         if (take_mmap_sem)
285                 up_write(&mm->mmap_sem);
286         kfree(mmu_notifier_mm);
287 out:
288         BUG_ON(atomic_read(&mm->mm_users) <= 0);
289         return ret;
290 }
291 
292 /*
293  * Must not hold mmap_sem nor any other VM related lock when calling
294  * this registration function. Must also ensure mm_users can't go down
295  * to zero while this runs to avoid races with mmu_notifier_release,
296  * so mm has to be current->mm or the mm should be pinned safely such
297  * as with get_task_mm(). If the mm is not current->mm, the mm_users
298  * pin should be released by calling mmput after mmu_notifier_register
299  * returns. mmu_notifier_unregister must be always called to
300  * unregister the notifier. mm_count is automatically pinned to allow
301  * mmu_notifier_unregister to safely run at any time later, before or
302  * after exit_mmap. ->release will always be called before exit_mmap
303  * frees the pages.
304  */
305 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
306 {
307         return do_mmu_notifier_register(mn, mm, 1);
308 }
309 EXPORT_SYMBOL_GPL(mmu_notifier_register);
310 
311 /*
312  * Same as mmu_notifier_register but here the caller must hold the
313  * mmap_sem in write mode.
314  */
315 int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
316 {
317         return do_mmu_notifier_register(mn, mm, 0);
318 }
319 EXPORT_SYMBOL_GPL(__mmu_notifier_register);
320 
321 /* this is called after the last mmu_notifier_unregister() returned */
322 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
323 {
324         BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
325         kfree(mm->mmu_notifier_mm);
326         mm->mmu_notifier_mm = LIST_POISON1; /* debug */
327 }
328 
329 /*
330  * This releases the mm_count pin automatically and frees the mm
331  * structure if it was the last user of it. It serializes against
332  * running mmu notifiers with SRCU and against mmu_notifier_unregister
333  * with the unregister lock + SRCU. All sptes must be dropped before
334  * calling mmu_notifier_unregister. ->release or any other notifier
335  * method may be invoked concurrently with mmu_notifier_unregister,
336  * and only after mmu_notifier_unregister returned we're guaranteed
337  * that ->release or any other method can't run anymore.
338  */
339 void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
340 {
341         BUG_ON(atomic_read(&mm->mm_count) <= 0);
342 
343         if (!hlist_unhashed(&mn->hlist)) {
344                 /*
345                  * SRCU here will force exit_mmap to wait for ->release to
346                  * finish before freeing the pages.
347                  */
348                 int id;
349 
350                 id = srcu_read_lock(&srcu);
351                 /*
352                  * exit_mmap will block in mmu_notifier_release to guarantee
353                  * that ->release is called before freeing the pages.
354                  */
355                 if (mn->ops->release)
356                         mn->ops->release(mn, mm);
357                 srcu_read_unlock(&srcu, id);
358 
359                 spin_lock(&mm->mmu_notifier_mm->lock);
360                 /*
361                  * Can not use list_del_rcu() since __mmu_notifier_release
362                  * can delete it before we hold the lock.
363                  */
364                 hlist_del_init_rcu(&mn->hlist);
365                 spin_unlock(&mm->mmu_notifier_mm->lock);
366         }
367 
368         /*
369          * Wait for any running method to finish, of course including
370          * ->release if it was run by mmu_notifier_release instead of us.
371          */
372         synchronize_srcu(&srcu);
373 
374         BUG_ON(atomic_read(&mm->mm_count) <= 0);
375 
376         mmdrop(mm);
377 }
378 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
379 
380 /*
381  * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
382  */
383 void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
384                                         struct mm_struct *mm)
385 {
386         spin_lock(&mm->mmu_notifier_mm->lock);
387         /*
388          * Can not use list_del_rcu() since __mmu_notifier_release
389          * can delete it before we hold the lock.
390          */
391         hlist_del_init_rcu(&mn->hlist);
392         spin_unlock(&mm->mmu_notifier_mm->lock);
393 
394         BUG_ON(atomic_read(&mm->mm_count) <= 0);
395         mmdrop(mm);
396 }
397 EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
398 

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