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

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