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/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 void mmu_notifier_synchronize(void)
  39 {
  40         /* Wait for any running method to finish. */
  41         srcu_barrier(&srcu);
  42 }
  43 EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
  44
  45 /*
  46  * This function can't run concurrently against mmu_notifier_register
  47  * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
  48  * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
  49  * in parallel despite there being no task using this mm any more,
  50  * through the vmas outside of the exit_mmap context, such as with
  51  * vmtruncate. This serializes against mmu_notifier_unregister with
  52  * the mmu_notifier_mm->lock in addition to SRCU and it serializes
  53  * against the other mmu notifiers with SRCU. struct mmu_notifier_mm
  54  * can't go away from under us as exit_mmap holds an mm_count pin
  55  * itself.
  56  */
  57 void __mmu_notifier_release(struct mm_struct *mm)
  58 {
  59         struct mmu_notifier *mn;
  60         int id;
  61
  62         /*
  63          * SRCU here will block mmu_notifier_unregister until
  64          * ->release returns.
  65          */
  66         id = srcu_read_lock(&srcu);
  67         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
  68                 /*
  69                  * If ->release runs before mmu_notifier_unregister it must be
  70                  * handled, as it's the only way for the driver to flush all
  71                  * existing sptes and stop the driver from establishing any more
  72                  * sptes before all the pages in the mm are freed.
  73                  */
  74                 if (mn->ops->release)
  75                         mn->ops->release(mn, mm);
  76
  77         spin_lock(&mm->mmu_notifier_mm->lock);
  78         while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
  79                 mn = hlist_entry(mm->mmu_notifier_mm->list.first,
  80                                  struct mmu_notifier,
  81                                  hlist);
  82                 /*
  83                  * We arrived before mmu_notifier_unregister so
  84                  * mmu_notifier_unregister will do nothing other than to wait
  85                  * for ->release to finish and for mmu_notifier_unregister to
  86                  * return.
  87                  */
  88                 hlist_del_init_rcu(&mn->hlist);
  89         }
  90         spin_unlock(&mm->mmu_notifier_mm->lock);
  91         srcu_read_unlock(&srcu, id);
  92
  93         /*
  94          * synchronize_srcu here prevents mmu_notifier_release from returning to
  95          * exit_mmap (which would proceed with freeing all pages in the mm)
  96          * until the ->release method returns, if it was invoked by
  97          * mmu_notifier_unregister.
  98          *
  99          * The mmu_notifier_mm can't go away from under us because one mm_count
 100          * is held by exit_mmap.
 101          */
 102         synchronize_srcu(&srcu);
 103 }
 104
 105 /*
 106  * If no young bitflag is supported by the hardware, ->clear_flush_young can
 107  * unmap the address and return 1 or 0 depending if the mapping previously
 108  * existed or not.
 109  */
 110 int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
 111                                         unsigned long start,
 112                                         unsigned long end)
 113 {
 114         struct mmu_notifier *mn;
 115         int young = 0, id;
 116
 117         id = srcu_read_lock(&srcu);
 118         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 119                 if (mn->ops->clear_flush_young)
 120                         young |= mn->ops->clear_flush_young(mn, mm, start, end);
 121         }
 122         srcu_read_unlock(&srcu, id);
 123
 124         return young;
 125 }
 126
 127 int __mmu_notifier_clear_young(struct mm_struct *mm,
 128                                unsigned long start,
 129                                unsigned long end)
 130 {
 131         struct mmu_notifier *mn;
 132         int young = 0, id;
 133
 134         id = srcu_read_lock(&srcu);
 135         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 136                 if (mn->ops->clear_young)
 137                         young |= mn->ops->clear_young(mn, mm, start, end);
 138         }
 139         srcu_read_unlock(&srcu, id);
 140
 141         return young;
 142 }
 143
 144 int __mmu_notifier_test_young(struct mm_struct *mm,
 145                               unsigned long address)
 146 {
 147         struct mmu_notifier *mn;
 148         int young = 0, id;
 149
 150         id = srcu_read_lock(&srcu);
 151         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 152                 if (mn->ops->test_young) {
 153                         young = mn->ops->test_young(mn, mm, address);
 154                         if (young)
 155                                 break;
 156                 }
 157         }
 158         srcu_read_unlock(&srcu, id);
 159
 160         return young;
 161 }
 162
 163 void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
 164                                pte_t pte)
 165 {
 166         struct mmu_notifier *mn;
 167         int id;
 168
 169         id = srcu_read_lock(&srcu);
 170         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 171                 if (mn->ops->change_pte)
 172                         mn->ops->change_pte(mn, mm, address, pte);
 173         }
 174         srcu_read_unlock(&srcu, id);
 175 }
 176
 177 int __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
 178                                   unsigned long start, unsigned long end,
 179                                   bool blockable)
 180 {
 181         struct mmu_notifier *mn;
 182         int ret = 0;
 183         int id;
 184
 185         id = srcu_read_lock(&srcu);
 186         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 187                 if (mn->ops->invalidate_range_start) {
 188                         int _ret = mn->ops->invalidate_range_start(mn, mm, start, end, blockable);
 189                         if (_ret) {
 190                                 pr_info("%pS callback failed with %d in %sblockable context.\n",
 191                                                 mn->ops->invalidate_range_start, _ret,
 192                                                 !blockable ? "non-" : "");
 193                                 ret = _ret;
 194                         }
 195                 }
 196         }
 197         srcu_read_unlock(&srcu, id);
 198
 199         return ret;
 200 }
 201 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
 202
 203 void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
 204                                          unsigned long start,
 205                                          unsigned long end,
 206                                          bool only_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                  * We skip call to invalidate_range() if we know it is safe ie
 222                  * call site use mmu_notifier_invalidate_range_only_end() which
 223                  * is safe to do when we know that a call to invalidate_range()
 224                  * already happen under page table lock.
 225                  */
 226                 if (!only_end && mn->ops->invalidate_range)
 227                         mn->ops->invalidate_range(mn, mm, start, end);
 228                 if (mn->ops->invalidate_range_end)
 229                         mn->ops->invalidate_range_end(mn, mm, start, end);
 230         }
 231         srcu_read_unlock(&srcu, id);
 232 }
 233 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
 234
 235 void __mmu_notifier_invalidate_range(struct mm_struct *mm,
 236                                   unsigned long start, unsigned long end)
 237 {
 238         struct mmu_notifier *mn;
 239         int id;
 240
 241         id = srcu_read_lock(&srcu);
 242         hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 243                 if (mn->ops->invalidate_range)
 244                         mn->ops->invalidate_range(mn, mm, start, end);
 245         }
 246         srcu_read_unlock(&srcu, id);
 247 }
 248 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
 249
 250 static int do_mmu_notifier_register(struct mmu_notifier *mn,
 251                                     struct mm_struct *mm,
 252                                     int take_mmap_sem)
 253 {
 254         struct mmu_notifier_mm *mmu_notifier_mm;
 255         int ret;
 256
 257         BUG_ON(atomic_read(&mm->mm_users) <= 0);
 258
 259         ret = -ENOMEM;
 260         mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
 261         if (unlikely(!mmu_notifier_mm))
 262                 goto out;
 263
 264         if (take_mmap_sem)
 265                 down_write(&mm->mmap_sem);
 266         ret = mm_take_all_locks(mm);
 267         if (unlikely(ret))
 268                 goto out_clean;
 269
 270         if (!mm_has_notifiers(mm)) {
 271                 INIT_HLIST_HEAD(&mmu_notifier_mm->list);
 272                 spin_lock_init(&mmu_notifier_mm->lock);
 273
 274                 mm->mmu_notifier_mm = mmu_notifier_mm;
 275                 mmu_notifier_mm = NULL;
 276         }
 277         mmgrab(mm);
 278
 279         /*
 280          * Serialize the update against mmu_notifier_unregister. A
 281          * side note: mmu_notifier_release can't run concurrently with
 282          * us because we hold the mm_users pin (either implicitly as
 283          * current->mm or explicitly with get_task_mm() or similar).
 284          * We can't race against any other mmu notifier method either
 285          * thanks to mm_take_all_locks().
 286          */
 287         spin_lock(&mm->mmu_notifier_mm->lock);
 288         hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
 289         spin_unlock(&mm->mmu_notifier_mm->lock);
 290
 291         mm_drop_all_locks(mm);
 292 out_clean:
 293         if (take_mmap_sem)
 294                 up_write(&mm->mmap_sem);
 295         kfree(mmu_notifier_mm);
 296 out:
 297         BUG_ON(atomic_read(&mm->mm_users) <= 0);
 298         return ret;
 299 }
 300
 301 /*
 302  * Must not hold mmap_sem nor any other VM related lock when calling
 303  * this registration function. Must also ensure mm_users can't go down
 304  * to zero while this runs to avoid races with mmu_notifier_release,
 305  * so mm has to be current->mm or the mm should be pinned safely such
 306  * as with get_task_mm(). If the mm is not current->mm, the mm_users
 307  * pin should be released by calling mmput after mmu_notifier_register
 308  * returns. mmu_notifier_unregister must be always called to
 309  * unregister the notifier. mm_count is automatically pinned to allow
 310  * mmu_notifier_unregister to safely run at any time later, before or
 311  * after exit_mmap. ->release will always be called before exit_mmap
 312  * frees the pages.
 313  */
 314 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 315 {
 316         return do_mmu_notifier_register(mn, mm, 1);
 317 }
 318 EXPORT_SYMBOL_GPL(mmu_notifier_register);
 319
 320 /*
 321  * Same as mmu_notifier_register but here the caller must hold the
 322  * mmap_sem in write mode.
 323  */
 324 int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 325 {
 326         return do_mmu_notifier_register(mn, mm, 0);
 327 }
 328 EXPORT_SYMBOL_GPL(__mmu_notifier_register);
 329
 330 /* this is called after the last mmu_notifier_unregister() returned */
 331 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
 332 {
 333         BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
 334         kfree(mm->mmu_notifier_mm);
 335         mm->mmu_notifier_mm = LIST_POISON1; /* debug */
 336 }
 337
 338 /*
 339  * This releases the mm_count pin automatically and frees the mm
 340  * structure if it was the last user of it. It serializes against
 341  * running mmu notifiers with SRCU and against mmu_notifier_unregister
 342  * with the unregister lock + SRCU. All sptes must be dropped before
 343  * calling mmu_notifier_unregister. ->release or any other notifier
 344  * method may be invoked concurrently with mmu_notifier_unregister,
 345  * and only after mmu_notifier_unregister returned we're guaranteed
 346  * that ->release or any other method can't run anymore.
 347  */
 348 void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
 349 {
 350         BUG_ON(atomic_read(&mm->mm_count) <= 0);
 351
 352         if (!hlist_unhashed(&mn->hlist)) {
 353                 /*
 354                  * SRCU here will force exit_mmap to wait for ->release to
 355                  * finish before freeing the pages.
 356                  */
 357                 int id;
 358
 359                 id = srcu_read_lock(&srcu);
 360                 /*
 361                  * exit_mmap will block in mmu_notifier_release to guarantee
 362                  * that ->release is called before freeing the pages.
 363                  */
 364                 if (mn->ops->release)
 365                         mn->ops->release(mn, mm);
 366                 srcu_read_unlock(&srcu, id);
 367
 368                 spin_lock(&mm->mmu_notifier_mm->lock);
 369                 /*
 370                  * Can not use list_del_rcu() since __mmu_notifier_release
 371                  * can delete it before we hold the lock.
 372                  */
 373                 hlist_del_init_rcu(&mn->hlist);
 374                 spin_unlock(&mm->mmu_notifier_mm->lock);
 375         }
 376
 377         /*
 378          * Wait for any running method to finish, of course including
 379          * ->release if it was run by mmu_notifier_release instead of us.
 380          */
 381         synchronize_srcu(&srcu);
 382
 383         BUG_ON(atomic_read(&mm->mm_count) <= 0);
 384
 385         mmdrop(mm);
 386 }
 387 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
 388
 389 /*
 390  * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
 391  */
 392 void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
 393                                         struct mm_struct *mm)
 394 {
 395         spin_lock(&mm->mmu_notifier_mm->lock);
 396         /*
 397          * Can not use list_del_rcu() since __mmu_notifier_release
 398          * can delete it before we hold the lock.
 399          */
 400         hlist_del_init_rcu(&mn->hlist);
 401         spin_unlock(&mm->mmu_notifier_mm->lock);
 402
 403         BUG_ON(atomic_read(&mm->mm_count) <= 0);
 404         mmdrop(mm);
 405 }
 406 EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);