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 */
  23static 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 */
  37void __mmu_notifier_release(struct mm_struct *mm)
  38{
  39        struct mmu_notifier *mn;
  40        int id;
  41
  42        /*
  43         * srcu_read_lock() here will block synchronize_srcu() in
  44         * mmu_notifier_unregister() until all registered
  45         * ->release() callouts this function makes have
  46         * returned.
  47         */
  48        id = srcu_read_lock(&srcu);
  49        spin_lock(&mm->mmu_notifier_mm->lock);
  50        while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
  51                mn = hlist_entry(mm->mmu_notifier_mm->list.first,
  52                                 struct mmu_notifier,
  53                                 hlist);
  54
  55                /*
  56                 * Unlink.  This will prevent mmu_notifier_unregister()
  57                 * from also making the ->release() callout.
  58                 */
  59                hlist_del_init_rcu(&mn->hlist);
  60                spin_unlock(&mm->mmu_notifier_mm->lock);
  61
  62                /*
  63                 * Clear sptes. (see 'release' description in mmu_notifier.h)
  64                 */
  65                if (mn->ops->release)
  66                        mn->ops->release(mn, mm);
  67
  68                spin_lock(&mm->mmu_notifier_mm->lock);
  69        }
  70        spin_unlock(&mm->mmu_notifier_mm->lock);
  71
  72        /*
  73         * All callouts to ->release() which we have done are complete.
  74         * Allow synchronize_srcu() in mmu_notifier_unregister() to complete
  75         */
  76        srcu_read_unlock(&srcu, id);
  77
  78        /*
  79         * mmu_notifier_unregister() may have unlinked a notifier and may
  80         * still be calling out to it.  Additionally, other notifiers
  81         * may have been active via vmtruncate() et. al. Block here
  82         * to ensure that all notifier callouts for this mm have been
  83         * completed and the sptes are really cleaned up before returning
  84         * to exit_mmap().
  85         */
  86        synchronize_srcu(&srcu);
  87}
  88
  89/*
  90 * If no young bitflag is supported by the hardware, ->clear_flush_young can
  91 * unmap the address and return 1 or 0 depending if the mapping previously
  92 * existed or not.
  93 */
  94int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
  95                                        unsigned long address)
  96{
  97        struct mmu_notifier *mn;
  98        int young = 0, id;
  99
 100        id = srcu_read_lock(&srcu);
 101        hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 102                if (mn->ops->clear_flush_young)
 103                        young |= mn->ops->clear_flush_young(mn, mm, address);
 104        }
 105        srcu_read_unlock(&srcu, id);
 106
 107        return young;
 108}
 109
 110int __mmu_notifier_test_young(struct mm_struct *mm,
 111                              unsigned long address)
 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->test_young) {
 119                        young = mn->ops->test_young(mn, mm, address);
 120                        if (young)
 121                                break;
 122                }
 123        }
 124        srcu_read_unlock(&srcu, id);
 125
 126        return young;
 127}
 128
 129void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
 130                               pte_t pte)
 131{
 132        struct mmu_notifier *mn;
 133        int 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->change_pte)
 138                        mn->ops->change_pte(mn, mm, address, pte);
 139        }
 140        srcu_read_unlock(&srcu, id);
 141}
 142
 143void __mmu_notifier_invalidate_page(struct mm_struct *mm,
 144                                          unsigned long address)
 145{
 146        struct mmu_notifier *mn;
 147        int id;
 148
 149        id = srcu_read_lock(&srcu);
 150        hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 151                if (mn->ops->invalidate_page)
 152                        mn->ops->invalidate_page(mn, mm, address);
 153        }
 154        srcu_read_unlock(&srcu, id);
 155}
 156
 157void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
 158                                  unsigned long start, unsigned long end)
 159{
 160        struct mmu_notifier *mn;
 161        int id;
 162
 163        id = srcu_read_lock(&srcu);
 164        hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 165                if (mn->ops->invalidate_range_start)
 166                        mn->ops->invalidate_range_start(mn, mm, start, end);
 167        }
 168        srcu_read_unlock(&srcu, id);
 169}
 170EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
 171
 172void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
 173                                  unsigned long start, unsigned long end)
 174{
 175        struct mmu_notifier *mn;
 176        int id;
 177
 178        id = srcu_read_lock(&srcu);
 179        hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
 180                if (mn->ops->invalidate_range_end)
 181                        mn->ops->invalidate_range_end(mn, mm, start, end);
 182        }
 183        srcu_read_unlock(&srcu, id);
 184}
 185EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
 186
 187static int do_mmu_notifier_register(struct mmu_notifier *mn,
 188                                    struct mm_struct *mm,
 189                                    int take_mmap_sem)
 190{
 191        struct mmu_notifier_mm *mmu_notifier_mm;
 192        int ret;
 193
 194        BUG_ON(atomic_read(&mm->mm_users) <= 0);
 195
 196        /*
 197         * Verify that mmu_notifier_init() already run and the global srcu is
 198         * initialized.
 199         */
 200        BUG_ON(!srcu.per_cpu_ref);
 201
 202        ret = -ENOMEM;
 203        mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
 204        if (unlikely(!mmu_notifier_mm))
 205                goto out;
 206
 207        if (take_mmap_sem)
 208                down_write(&mm->mmap_sem);
 209        ret = mm_take_all_locks(mm);
 210        if (unlikely(ret))
 211                goto out_clean;
 212
 213        if (!mm_has_notifiers(mm)) {
 214                INIT_HLIST_HEAD(&mmu_notifier_mm->list);
 215                spin_lock_init(&mmu_notifier_mm->lock);
 216
 217                mm->mmu_notifier_mm = mmu_notifier_mm;
 218                mmu_notifier_mm = NULL;
 219        }
 220        atomic_inc(&mm->mm_count);
 221
 222        /*
 223         * Serialize the update against mmu_notifier_unregister. A
 224         * side note: mmu_notifier_release can't run concurrently with
 225         * us because we hold the mm_users pin (either implicitly as
 226         * current->mm or explicitly with get_task_mm() or similar).
 227         * We can't race against any other mmu notifier method either
 228         * thanks to mm_take_all_locks().
 229         */
 230        spin_lock(&mm->mmu_notifier_mm->lock);
 231        hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
 232        spin_unlock(&mm->mmu_notifier_mm->lock);
 233
 234        mm_drop_all_locks(mm);
 235out_clean:
 236        if (take_mmap_sem)
 237                up_write(&mm->mmap_sem);
 238        kfree(mmu_notifier_mm);
 239out:
 240        BUG_ON(atomic_read(&mm->mm_users) <= 0);
 241        return ret;
 242}
 243
 244/*
 245 * Must not hold mmap_sem nor any other VM related lock when calling
 246 * this registration function. Must also ensure mm_users can't go down
 247 * to zero while this runs to avoid races with mmu_notifier_release,
 248 * so mm has to be current->mm or the mm should be pinned safely such
 249 * as with get_task_mm(). If the mm is not current->mm, the mm_users
 250 * pin should be released by calling mmput after mmu_notifier_register
 251 * returns. mmu_notifier_unregister must be always called to
 252 * unregister the notifier. mm_count is automatically pinned to allow
 253 * mmu_notifier_unregister to safely run at any time later, before or
 254 * after exit_mmap. ->release will always be called before exit_mmap
 255 * frees the pages.
 256 */
 257int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 258{
 259        return do_mmu_notifier_register(mn, mm, 1);
 260}
 261EXPORT_SYMBOL_GPL(mmu_notifier_register);
 262
 263/*
 264 * Same as mmu_notifier_register but here the caller must hold the
 265 * mmap_sem in write mode.
 266 */
 267int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 268{
 269        return do_mmu_notifier_register(mn, mm, 0);
 270}
 271EXPORT_SYMBOL_GPL(__mmu_notifier_register);
 272
 273/* this is called after the last mmu_notifier_unregister() returned */
 274void __mmu_notifier_mm_destroy(struct mm_struct *mm)
 275{
 276        BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
 277        kfree(mm->mmu_notifier_mm);
 278        mm->mmu_notifier_mm = LIST_POISON1; /* debug */
 279}
 280
 281/*
 282 * This releases the mm_count pin automatically and frees the mm
 283 * structure if it was the last user of it. It serializes against
 284 * running mmu notifiers with SRCU and against mmu_notifier_unregister
 285 * with the unregister lock + SRCU. All sptes must be dropped before
 286 * calling mmu_notifier_unregister. ->release or any other notifier
 287 * method may be invoked concurrently with mmu_notifier_unregister,
 288 * and only after mmu_notifier_unregister returned we're guaranteed
 289 * that ->release or any other method can't run anymore.
 290 */
 291void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
 292{
 293        BUG_ON(atomic_read(&mm->mm_count) <= 0);
 294
 295        spin_lock(&mm->mmu_notifier_mm->lock);
 296        if (!hlist_unhashed(&mn->hlist)) {
 297                int id;
 298
 299                /*
 300                 * Ensure we synchronize up with __mmu_notifier_release().
 301                 */
 302                id = srcu_read_lock(&srcu);
 303
 304                hlist_del_rcu(&mn->hlist);
 305                spin_unlock(&mm->mmu_notifier_mm->lock);
 306
 307                if (mn->ops->release)
 308                        mn->ops->release(mn, mm);
 309
 310                /*
 311                 * Allow __mmu_notifier_release() to complete.
 312                 */
 313                srcu_read_unlock(&srcu, id);
 314        } else
 315                spin_unlock(&mm->mmu_notifier_mm->lock);
 316
 317        /*
 318         * Wait for any running method to finish, including ->release() if it
 319         * was run by __mmu_notifier_release() instead of us.
 320         */
 321        synchronize_srcu(&srcu);
 322
 323        BUG_ON(atomic_read(&mm->mm_count) <= 0);
 324
 325        mmdrop(mm);
 326}
 327EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
 328
 329static int __init mmu_notifier_init(void)
 330{
 331        return init_srcu_struct(&srcu);
 332}
 333
 334module_init(mmu_notifier_init);
 335
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