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 <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);