root/mm/mmu_notifier.c

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DEFINITIONS

This source file includes following definitions.
  1. __mmu_notifier_release
  2. __mmu_notifier_clear_flush_young
  3. __mmu_notifier_clear_young
  4. __mmu_notifier_test_young
  5. __mmu_notifier_change_pte
  6. __mmu_notifier_invalidate_range_start
  7. __mmu_notifier_invalidate_range_end
  8. __mmu_notifier_invalidate_range
  9. __mmu_notifier_register
  10. mmu_notifier_register
  11. find_get_mmu_notifier
  12. mmu_notifier_get_locked
  13. __mmu_notifier_mm_destroy
  14. mmu_notifier_unregister
  15. mmu_notifier_free_rcu
  16. mmu_notifier_put
  17. mmu_notifier_synchronize
  18. mmu_notifier_range_update_to_read_only

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  linux/mm/mmu_notifier.c
   4  *
   5  *  Copyright (C) 2008  Qumranet, Inc.
   6  *  Copyright (C) 2008  SGI
   7  *             Christoph Lameter <cl@linux.com>
   8  */
   9 
  10 #include <linux/rculist.h>
  11 #include <linux/mmu_notifier.h>
  12 #include <linux/export.h>
  13 #include <linux/mm.h>
  14 #include <linux/err.h>
  15 #include <linux/srcu.h>
  16 #include <linux/rcupdate.h>
  17 #include <linux/sched.h>
  18 #include <linux/sched/mm.h>
  19 #include <linux/slab.h>
  20 
  21 /* global SRCU for all MMs */
  22 DEFINE_STATIC_SRCU(srcu);
  23 
  24 #ifdef CONFIG_LOCKDEP
  25 struct lockdep_map __mmu_notifier_invalidate_range_start_map = {
  26         .name = "mmu_notifier_invalidate_range_start"
  27 };
  28 #endif
  29 
  30 /*
  31  * This function can't run concurrently against mmu_notifier_register
  32  * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
  33  * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
  34  * in parallel despite there being no task using this mm any more,
  35  * through the vmas outside of the exit_mmap context, such as with
  36  * vmtruncate. This serializes against mmu_notifier_unregister with
  37  * the mmu_notifier_mm->lock in addition to SRCU and it serializes
  38  * against the other mmu notifiers with SRCU. struct mmu_notifier_mm
  39  * can't go away from under us as exit_mmap holds an mm_count pin
  40  * itself.
  41  */
  42 void __mmu_notifier_release(struct mm_struct *mm)
  43 {
  44         struct mmu_notifier *mn;
  45         int id;
  46 
  47         /*
  48          * SRCU here will block mmu_notifier_unregister until
  49          * ->release returns.
  50          */
  51         id = srcu_read_lock(&srcu);
  52         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
  53                 /*
  54                  * If ->release runs before mmu_notifier_unregister it must be
  55                  * handled, as it's the only way for the driver to flush all
  56                  * existing sptes and stop the driver from establishing any more
  57                  * sptes before all the pages in the mm are freed.
  58                  */
  59                 if (mn->ops->release)
  60                         mn->ops->release(mn, mm);
  61 
  62         spin_lock(&mm->mmu_notifier_mm->lock);
  63         while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
  64                 mn = hlist_entry(mm->mmu_notifier_mm->list.first,
  65                                  struct mmu_notifier,
  66                                  hlist);
  67                 /*
  68                  * We arrived before mmu_notifier_unregister so
  69                  * mmu_notifier_unregister will do nothing other than to wait
  70                  * for ->release to finish and for mmu_notifier_unregister to
  71                  * return.
  72                  */
  73                 hlist_del_init_rcu(&mn->hlist);
  74         }
  75         spin_unlock(&mm->mmu_notifier_mm->lock);
  76         srcu_read_unlock(&srcu, id);
  77 
  78         /*
  79          * synchronize_srcu here prevents mmu_notifier_release from returning to
  80          * exit_mmap (which would proceed with freeing all pages in the mm)
  81          * until the ->release method returns, if it was invoked by
  82          * mmu_notifier_unregister.
  83          *
  84          * The mmu_notifier_mm can't go away from under us because one mm_count
  85          * is held by exit_mmap.
  86          */
  87         synchronize_srcu(&srcu);
  88 }
  89 
  90 /*
  91  * If no young bitflag is supported by the hardware, ->clear_flush_young can
  92  * unmap the address and return 1 or 0 depending if the mapping previously
  93  * existed or not.
  94  */
  95 int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
  96                                         unsigned long start,
  97                                         unsigned long end)
  98 {
  99         struct mmu_notifier *mn;
 100         int young = 0, id;
 101 
 102         id = srcu_read_lock(&srcu);
 103         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 104                 if (mn->ops->clear_flush_young)
 105                         young |= mn->ops->clear_flush_young(mn, mm, start, end);
 106         }
 107         srcu_read_unlock(&srcu, id);
 108 
 109         return young;
 110 }
 111 
 112 int __mmu_notifier_clear_young(struct mm_struct *mm,
 113                                unsigned long start,
 114                                unsigned long end)
 115 {
 116         struct mmu_notifier *mn;
 117         int young = 0, id;
 118 
 119         id = srcu_read_lock(&srcu);
 120         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 121                 if (mn->ops->clear_young)
 122                         young |= mn->ops->clear_young(mn, mm, start, end);
 123         }
 124         srcu_read_unlock(&srcu, id);
 125 
 126         return young;
 127 }
 128 
 129 int __mmu_notifier_test_young(struct mm_struct *mm,
 130                               unsigned long address)
 131 {
 132         struct mmu_notifier *mn;
 133         int young = 0, id;
 134 
 135         id = srcu_read_lock(&srcu);
 136         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 137                 if (mn->ops->test_young) {
 138                         young = mn->ops->test_young(mn, mm, address);
 139                         if (young)
 140                                 break;
 141                 }
 142         }
 143         srcu_read_unlock(&srcu, id);
 144 
 145         return young;
 146 }
 147 
 148 void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
 149                                pte_t pte)
 150 {
 151         struct mmu_notifier *mn;
 152         int id;
 153 
 154         id = srcu_read_lock(&srcu);
 155         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 156                 if (mn->ops->change_pte)
 157                         mn->ops->change_pte(mn, mm, address, pte);
 158         }
 159         srcu_read_unlock(&srcu, id);
 160 }
 161 
 162 int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
 163 {
 164         struct mmu_notifier *mn;
 165         int ret = 0;
 166         int id;
 167 
 168         id = srcu_read_lock(&srcu);
 169         hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {
 170                 if (mn->ops->invalidate_range_start) {
 171                         int _ret;
 172 
 173                         if (!mmu_notifier_range_blockable(range))
 174                                 non_block_start();
 175                         _ret = mn->ops->invalidate_range_start(mn, range);
 176                         if (!mmu_notifier_range_blockable(range))
 177                                 non_block_end();
 178                         if (_ret) {
 179                                 pr_info("%pS callback failed with %d in %sblockable context.\n",
 180                                         mn->ops->invalidate_range_start, _ret,
 181                                         !mmu_notifier_range_blockable(range) ? "non-" : "");
 182                                 WARN_ON(mmu_notifier_range_blockable(range) ||
 183                                         _ret != -EAGAIN);
 184                                 ret = _ret;
 185                         }
 186                 }
 187         }
 188         srcu_read_unlock(&srcu, id);
 189 
 190         return ret;
 191 }
 192 
 193 void __mmu_notifier_invalidate_range_end(struct mmu_notifier_range *range,
 194                                          bool only_end)
 195 {
 196         struct mmu_notifier *mn;
 197         int id;
 198 
 199         lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
 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                         if (!mmu_notifier_range_blockable(range))
 221                                 non_block_start();
 222                         mn->ops->invalidate_range_end(mn, range);
 223                         if (!mmu_notifier_range_blockable(range))
 224                                 non_block_end();
 225                 }
 226         }
 227         srcu_read_unlock(&srcu, id);
 228         lock_map_release(&__mmu_notifier_invalidate_range_start_map);
 229 }
 230 
 231 void __mmu_notifier_invalidate_range(struct mm_struct *mm,
 232                                   unsigned long start, unsigned long end)
 233 {
 234         struct mmu_notifier *mn;
 235         int id;
 236 
 237         id = srcu_read_lock(&srcu);
 238         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 239                 if (mn->ops->invalidate_range)
 240                         mn->ops->invalidate_range(mn, mm, start, end);
 241         }
 242         srcu_read_unlock(&srcu, id);
 243 }
 244 
 245 /*
 246  * Same as mmu_notifier_register but here the caller must hold the
 247  * mmap_sem in write mode.
 248  */
 249 int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 250 {
 251         struct mmu_notifier_mm *mmu_notifier_mm = NULL;
 252         int ret;
 253 
 254         lockdep_assert_held_write(&mm->mmap_sem);
 255         BUG_ON(atomic_read(&mm->mm_users) <= 0);
 256 
 257         if (IS_ENABLED(CONFIG_LOCKDEP)) {
 258                 fs_reclaim_acquire(GFP_KERNEL);
 259                 lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
 260                 lock_map_release(&__mmu_notifier_invalidate_range_start_map);
 261                 fs_reclaim_release(GFP_KERNEL);
 262         }
 263 
 264         mn->mm = mm;
 265         mn->users = 1;
 266 
 267         if (!mm->mmu_notifier_mm) {
 268                 /*
 269                  * kmalloc cannot be called under mm_take_all_locks(), but we
 270                  * know that mm->mmu_notifier_mm can't change while we hold
 271                  * the write side of the mmap_sem.
 272                  */
 273                 mmu_notifier_mm =
 274                         kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
 275                 if (!mmu_notifier_mm)
 276                         return -ENOMEM;
 277 
 278                 INIT_HLIST_HEAD(&mmu_notifier_mm->list);
 279                 spin_lock_init(&mmu_notifier_mm->lock);
 280         }
 281 
 282         ret = mm_take_all_locks(mm);
 283         if (unlikely(ret))
 284                 goto out_clean;
 285 
 286         /* Pairs with the mmdrop in mmu_notifier_unregister_* */
 287         mmgrab(mm);
 288 
 289         /*
 290          * Serialize the update against mmu_notifier_unregister. A
 291          * side note: mmu_notifier_release can't run concurrently with
 292          * us because we hold the mm_users pin (either implicitly as
 293          * current->mm or explicitly with get_task_mm() or similar).
 294          * We can't race against any other mmu notifier method either
 295          * thanks to mm_take_all_locks().
 296          */
 297         if (mmu_notifier_mm)
 298                 mm->mmu_notifier_mm = mmu_notifier_mm;
 299 
 300         spin_lock(&mm->mmu_notifier_mm->lock);
 301         hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier_mm->list);
 302         spin_unlock(&mm->mmu_notifier_mm->lock);
 303 
 304         mm_drop_all_locks(mm);
 305         BUG_ON(atomic_read(&mm->mm_users) <= 0);
 306         return 0;
 307 
 308 out_clean:
 309         kfree(mmu_notifier_mm);
 310         return ret;
 311 }
 312 EXPORT_SYMBOL_GPL(__mmu_notifier_register);
 313 
 314 /**
 315  * mmu_notifier_register - Register a notifier on a mm
 316  * @mn: The notifier to attach
 317  * @mm: The mm to attach the notifier to
 318  *
 319  * Must not hold mmap_sem nor any other VM related lock when calling
 320  * this registration function. Must also ensure mm_users can't go down
 321  * to zero while this runs to avoid races with mmu_notifier_release,
 322  * so mm has to be current->mm or the mm should be pinned safely such
 323  * as with get_task_mm(). If the mm is not current->mm, the mm_users
 324  * pin should be released by calling mmput after mmu_notifier_register
 325  * returns.
 326  *
 327  * mmu_notifier_unregister() or mmu_notifier_put() must be always called to
 328  * unregister the notifier.
 329  *
 330  * While the caller has a mmu_notifier get the mn->mm pointer will remain
 331  * valid, and can be converted to an active mm pointer via mmget_not_zero().
 332  */
 333 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 334 {
 335         int ret;
 336 
 337         down_write(&mm->mmap_sem);
 338         ret = __mmu_notifier_register(mn, mm);
 339         up_write(&mm->mmap_sem);
 340         return ret;
 341 }
 342 EXPORT_SYMBOL_GPL(mmu_notifier_register);
 343 
 344 static struct mmu_notifier *
 345 find_get_mmu_notifier(struct mm_struct *mm, const struct mmu_notifier_ops *ops)
 346 {
 347         struct mmu_notifier *mn;
 348 
 349         spin_lock(&mm->mmu_notifier_mm->lock);
 350         hlist_for_each_entry_rcu (mn, &mm->mmu_notifier_mm->list, hlist) {
 351                 if (mn->ops != ops)
 352                         continue;
 353 
 354                 if (likely(mn->users != UINT_MAX))
 355                         mn->users++;
 356                 else
 357                         mn = ERR_PTR(-EOVERFLOW);
 358                 spin_unlock(&mm->mmu_notifier_mm->lock);
 359                 return mn;
 360         }
 361         spin_unlock(&mm->mmu_notifier_mm->lock);
 362         return NULL;
 363 }
 364 
 365 /**
 366  * mmu_notifier_get_locked - Return the single struct mmu_notifier for
 367  *                           the mm & ops
 368  * @ops: The operations struct being subscribe with
 369  * @mm : The mm to attach notifiers too
 370  *
 371  * This function either allocates a new mmu_notifier via
 372  * ops->alloc_notifier(), or returns an already existing notifier on the
 373  * list. The value of the ops pointer is used to determine when two notifiers
 374  * are the same.
 375  *
 376  * Each call to mmu_notifier_get() must be paired with a call to
 377  * mmu_notifier_put(). The caller must hold the write side of mm->mmap_sem.
 378  *
 379  * While the caller has a mmu_notifier get the mm pointer will remain valid,
 380  * and can be converted to an active mm pointer via mmget_not_zero().
 381  */
 382 struct mmu_notifier *mmu_notifier_get_locked(const struct mmu_notifier_ops *ops,
 383                                              struct mm_struct *mm)
 384 {
 385         struct mmu_notifier *mn;
 386         int ret;
 387 
 388         lockdep_assert_held_write(&mm->mmap_sem);
 389 
 390         if (mm->mmu_notifier_mm) {
 391                 mn = find_get_mmu_notifier(mm, ops);
 392                 if (mn)
 393                         return mn;
 394         }
 395 
 396         mn = ops->alloc_notifier(mm);
 397         if (IS_ERR(mn))
 398                 return mn;
 399         mn->ops = ops;
 400         ret = __mmu_notifier_register(mn, mm);
 401         if (ret)
 402                 goto out_free;
 403         return mn;
 404 out_free:
 405         mn->ops->free_notifier(mn);
 406         return ERR_PTR(ret);
 407 }
 408 EXPORT_SYMBOL_GPL(mmu_notifier_get_locked);
 409 
 410 /* this is called after the last mmu_notifier_unregister() returned */
 411 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
 412 {
 413         BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
 414         kfree(mm->mmu_notifier_mm);
 415         mm->mmu_notifier_mm = LIST_POISON1; /* debug */
 416 }
 417 
 418 /*
 419  * This releases the mm_count pin automatically and frees the mm
 420  * structure if it was the last user of it. It serializes against
 421  * running mmu notifiers with SRCU and against mmu_notifier_unregister
 422  * with the unregister lock + SRCU. All sptes must be dropped before
 423  * calling mmu_notifier_unregister. ->release or any other notifier
 424  * method may be invoked concurrently with mmu_notifier_unregister,
 425  * and only after mmu_notifier_unregister returned we're guaranteed
 426  * that ->release or any other method can't run anymore.
 427  */
 428 void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
 429 {
 430         BUG_ON(atomic_read(&mm->mm_count) <= 0);
 431 
 432         if (!hlist_unhashed(&mn->hlist)) {
 433                 /*
 434                  * SRCU here will force exit_mmap to wait for ->release to
 435                  * finish before freeing the pages.
 436                  */
 437                 int id;
 438 
 439                 id = srcu_read_lock(&srcu);
 440                 /*
 441                  * exit_mmap will block in mmu_notifier_release to guarantee
 442                  * that ->release is called before freeing the pages.
 443                  */
 444                 if (mn->ops->release)
 445                         mn->ops->release(mn, mm);
 446                 srcu_read_unlock(&srcu, id);
 447 
 448                 spin_lock(&mm->mmu_notifier_mm->lock);
 449                 /*
 450                  * Can not use list_del_rcu() since __mmu_notifier_release
 451                  * can delete it before we hold the lock.
 452                  */
 453                 hlist_del_init_rcu(&mn->hlist);
 454                 spin_unlock(&mm->mmu_notifier_mm->lock);
 455         }
 456 
 457         /*
 458          * Wait for any running method to finish, of course including
 459          * ->release if it was run by mmu_notifier_release instead of us.
 460          */
 461         synchronize_srcu(&srcu);
 462 
 463         BUG_ON(atomic_read(&mm->mm_count) <= 0);
 464 
 465         mmdrop(mm);
 466 }
 467 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
 468 
 469 static void mmu_notifier_free_rcu(struct rcu_head *rcu)
 470 {
 471         struct mmu_notifier *mn = container_of(rcu, struct mmu_notifier, rcu);
 472         struct mm_struct *mm = mn->mm;
 473 
 474         mn->ops->free_notifier(mn);
 475         /* Pairs with the get in __mmu_notifier_register() */
 476         mmdrop(mm);
 477 }
 478 
 479 /**
 480  * mmu_notifier_put - Release the reference on the notifier
 481  * @mn: The notifier to act on
 482  *
 483  * This function must be paired with each mmu_notifier_get(), it releases the
 484  * reference obtained by the get. If this is the last reference then process
 485  * to free the notifier will be run asynchronously.
 486  *
 487  * Unlike mmu_notifier_unregister() the get/put flow only calls ops->release
 488  * when the mm_struct is destroyed. Instead free_notifier is always called to
 489  * release any resources held by the user.
 490  *
 491  * As ops->release is not guaranteed to be called, the user must ensure that
 492  * all sptes are dropped, and no new sptes can be established before
 493  * mmu_notifier_put() is called.
 494  *
 495  * This function can be called from the ops->release callback, however the
 496  * caller must still ensure it is called pairwise with mmu_notifier_get().
 497  *
 498  * Modules calling this function must call mmu_notifier_synchronize() in
 499  * their __exit functions to ensure the async work is completed.
 500  */
 501 void mmu_notifier_put(struct mmu_notifier *mn)
 502 {
 503         struct mm_struct *mm = mn->mm;
 504 
 505         spin_lock(&mm->mmu_notifier_mm->lock);
 506         if (WARN_ON(!mn->users) || --mn->users)
 507                 goto out_unlock;
 508         hlist_del_init_rcu(&mn->hlist);
 509         spin_unlock(&mm->mmu_notifier_mm->lock);
 510 
 511         call_srcu(&srcu, &mn->rcu, mmu_notifier_free_rcu);
 512         return;
 513 
 514 out_unlock:
 515         spin_unlock(&mm->mmu_notifier_mm->lock);
 516 }
 517 EXPORT_SYMBOL_GPL(mmu_notifier_put);
 518 
 519 /**
 520  * mmu_notifier_synchronize - Ensure all mmu_notifiers are freed
 521  *
 522  * This function ensures that all outstanding async SRU work from
 523  * mmu_notifier_put() is completed. After it returns any mmu_notifier_ops
 524  * associated with an unused mmu_notifier will no longer be called.
 525  *
 526  * Before using the caller must ensure that all of its mmu_notifiers have been
 527  * fully released via mmu_notifier_put().
 528  *
 529  * Modules using the mmu_notifier_put() API should call this in their __exit
 530  * function to avoid module unloading races.
 531  */
 532 void mmu_notifier_synchronize(void)
 533 {
 534         synchronize_srcu(&srcu);
 535 }
 536 EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
 537 
 538 bool
 539 mmu_notifier_range_update_to_read_only(const struct mmu_notifier_range *range)
 540 {
 541         if (!range->vma || range->event != MMU_NOTIFY_PROTECTION_VMA)
 542                 return false;
 543         /* Return true if the vma still have the read flag set. */
 544         return range->vma->vm_flags & VM_READ;
 545 }
 546 EXPORT_SYMBOL_GPL(mmu_notifier_range_update_to_read_only);

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