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/module.h>
  15#include <linux/mm.h>
  16#include <linux/err.h>
  17#include <linux/rcupdate.h>
  18#include <linux/sched.h>
  19#include <linux/slab.h>
  20
  21/*
  22 * This function can't run concurrently against mmu_notifier_register
  23 * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
  24 * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
  25 * in parallel despite there being no task using this mm any more,
  26 * through the vmas outside of the exit_mmap context, such as with
  27 * vmtruncate. This serializes against mmu_notifier_unregister with
  28 * the mmu_notifier_mm->lock in addition to RCU and it serializes
  29 * against the other mmu notifiers with RCU. struct mmu_notifier_mm
  30 * can't go away from under us as exit_mmap holds an mm_count pin
  31 * itself.
  32 */
  33void __mmu_notifier_release(struct mm_struct *mm)
  34{
  35        struct mmu_notifier *mn;
  36
  37        spin_lock(&mm->mmu_notifier_mm->lock);
  38        while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
  39                mn = hlist_entry(mm->mmu_notifier_mm->list.first,
  40                                 struct mmu_notifier,
  41                                 hlist);
  42                /*
  43                 * We arrived before mmu_notifier_unregister so
  44                 * mmu_notifier_unregister will do nothing other than
  45                 * to wait ->release to finish and
  46                 * mmu_notifier_unregister to return.
  47                 */
  48                hlist_del_init_rcu(&mn->hlist);
  49                /*
  50                 * RCU here will block mmu_notifier_unregister until
  51                 * ->release returns.
  52                 */
  53                rcu_read_lock();
  54                spin_unlock(&mm->mmu_notifier_mm->lock);
  55                /*
  56                 * if ->release runs before mmu_notifier_unregister it
  57                 * must be handled as it's the only way for the driver
  58                 * to flush all existing sptes and stop the driver
  59                 * from establishing any more sptes before all the
  60                 * pages in the mm are freed.
  61                 */
  62                if (mn->ops->release)
  63                        mn->ops->release(mn, mm);
  64                rcu_read_unlock();
  65                spin_lock(&mm->mmu_notifier_mm->lock);
  66        }
  67        spin_unlock(&mm->mmu_notifier_mm->lock);
  68
  69        /*
  70         * synchronize_rcu here prevents mmu_notifier_release to
  71         * return to exit_mmap (which would proceed freeing all pages
  72         * in the mm) until the ->release method returns, if it was
  73         * invoked by mmu_notifier_unregister.
  74         *
  75         * The mmu_notifier_mm can't go away from under us because one
  76         * mm_count is hold by exit_mmap.
  77         */
  78        synchronize_rcu();
  79}
  80
  81/*
  82 * If no young bitflag is supported by the hardware, ->clear_flush_young can
  83 * unmap the address and return 1 or 0 depending if the mapping previously
  84 * existed or not.
  85 */
  86int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
  87                                        unsigned long address)
  88{
  89        struct mmu_notifier *mn;
  90        struct hlist_node *n;
  91        int young = 0;
  92
  93        rcu_read_lock();
  94        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
  95                if (mn->ops->clear_flush_young)
  96                        young |= mn->ops->clear_flush_young(mn, mm, address);
  97        }
  98        rcu_read_unlock();
  99
 100        return young;
 101}
 102
 103int __mmu_notifier_test_young(struct mm_struct *mm,
 104                              unsigned long address)
 105{
 106        struct mmu_notifier *mn;
 107        struct hlist_node *n;
 108        int young = 0;
 109
 110        rcu_read_lock();
 111        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
 112                if (mn->ops->test_young) {
 113                        young = mn->ops->test_young(mn, mm, address);
 114                        if (young)
 115                                break;
 116                }
 117        }
 118        rcu_read_unlock();
 119
 120        return young;
 121}
 122
 123void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
 124                               pte_t pte)
 125{
 126        struct mmu_notifier *mn;
 127        struct hlist_node *n;
 128
 129        rcu_read_lock();
 130        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
 131                if (mn->ops->change_pte)
 132                        mn->ops->change_pte(mn, mm, address, pte);
 133                /*
 134                 * Some drivers don't have change_pte,
 135                 * so we must call invalidate_page in that case.
 136                 */
 137                else if (mn->ops->invalidate_page)
 138                        mn->ops->invalidate_page(mn, mm, address);
 139        }
 140        rcu_read_unlock();
 141}
 142
 143void __mmu_notifier_invalidate_page(struct mm_struct *mm,
 144                                          unsigned long address)
 145{
 146        struct mmu_notifier *mn;
 147        struct hlist_node *n;
 148
 149        rcu_read_lock();
 150        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
 151                if (mn->ops->invalidate_page)
 152                        mn->ops->invalidate_page(mn, mm, address);
 153        }
 154        rcu_read_unlock();
 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        struct hlist_node *n;
 162
 163        rcu_read_lock();
 164        hlist_for_each_entry_rcu(mn, n, &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        rcu_read_unlock();
 169}
 170
 171void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
 172                                  unsigned long start, unsigned long end)
 173{
 174        struct mmu_notifier *mn;
 175        struct hlist_node *n;
 176
 177        rcu_read_lock();
 178        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
 179                if (mn->ops->invalidate_range_end)
 180                        mn->ops->invalidate_range_end(mn, mm, start, end);
 181        }
 182        rcu_read_unlock();
 183}
 184
 185static int do_mmu_notifier_register(struct mmu_notifier *mn,
 186                                    struct mm_struct *mm,
 187                                    int take_mmap_sem)
 188{
 189        struct mmu_notifier_mm *mmu_notifier_mm;
 190        int ret;
 191
 192        BUG_ON(atomic_read(&mm->mm_users) <= 0);
 193
 194        ret = -ENOMEM;
 195        mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
 196        if (unlikely(!mmu_notifier_mm))
 197                goto out;
 198
 199        if (take_mmap_sem)
 200                down_write(&mm->mmap_sem);
 201        ret = mm_take_all_locks(mm);
 202        if (unlikely(ret))
 203                goto out_cleanup;
 204
 205        if (!mm_has_notifiers(mm)) {
 206                INIT_HLIST_HEAD(&mmu_notifier_mm->list);
 207                spin_lock_init(&mmu_notifier_mm->lock);
 208                mm->mmu_notifier_mm = mmu_notifier_mm;
 209                mmu_notifier_mm = NULL;
 210        }
 211        atomic_inc(&mm->mm_count);
 212
 213        /*
 214         * Serialize the update against mmu_notifier_unregister. A
 215         * side note: mmu_notifier_release can't run concurrently with
 216         * us because we hold the mm_users pin (either implicitly as
 217         * current->mm or explicitly with get_task_mm() or similar).
 218         * We can't race against any other mmu notifier method either
 219         * thanks to mm_take_all_locks().
 220         */
 221        spin_lock(&mm->mmu_notifier_mm->lock);
 222        hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
 223        spin_unlock(&mm->mmu_notifier_mm->lock);
 224
 225        mm_drop_all_locks(mm);
 226out_cleanup:
 227        if (take_mmap_sem)
 228                up_write(&mm->mmap_sem);
 229        /* kfree() does nothing if mmu_notifier_mm is NULL */
 230        kfree(mmu_notifier_mm);
 231out:
 232        BUG_ON(atomic_read(&mm->mm_users) <= 0);
 233        return ret;
 234}
 235
 236/*
 237 * Must not hold mmap_sem nor any other VM related lock when calling
 238 * this registration function. Must also ensure mm_users can't go down
 239 * to zero while this runs to avoid races with mmu_notifier_release,
 240 * so mm has to be current->mm or the mm should be pinned safely such
 241 * as with get_task_mm(). If the mm is not current->mm, the mm_users
 242 * pin should be released by calling mmput after mmu_notifier_register
 243 * returns. mmu_notifier_unregister must be always called to
 244 * unregister the notifier. mm_count is automatically pinned to allow
 245 * mmu_notifier_unregister to safely run at any time later, before or
 246 * after exit_mmap. ->release will always be called before exit_mmap
 247 * frees the pages.
 248 */
 249int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 250{
 251        return do_mmu_notifier_register(mn, mm, 1);
 252}
 253EXPORT_SYMBOL_GPL(mmu_notifier_register);
 254
 255/*
 256 * Same as mmu_notifier_register but here the caller must hold the
 257 * mmap_sem in write mode.
 258 */
 259int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 260{
 261        return do_mmu_notifier_register(mn, mm, 0);
 262}
 263EXPORT_SYMBOL_GPL(__mmu_notifier_register);
 264
 265/* this is called after the last mmu_notifier_unregister() returned */
 266void __mmu_notifier_mm_destroy(struct mm_struct *mm)
 267{
 268        BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
 269        kfree(mm->mmu_notifier_mm);
 270        mm->mmu_notifier_mm = LIST_POISON1; /* debug */
 271}
 272
 273/*
 274 * This releases the mm_count pin automatically and frees the mm
 275 * structure if it was the last user of it. It serializes against
 276 * running mmu notifiers with RCU and against mmu_notifier_unregister
 277 * with the unregister lock + RCU. All sptes must be dropped before
 278 * calling mmu_notifier_unregister. ->release or any other notifier
 279 * method may be invoked concurrently with mmu_notifier_unregister,
 280 * and only after mmu_notifier_unregister returned we're guaranteed
 281 * that ->release or any other method can't run anymore.
 282 */
 283void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
 284{
 285        BUG_ON(atomic_read(&mm->mm_count) <= 0);
 286
 287        spin_lock(&mm->mmu_notifier_mm->lock);
 288        if (!hlist_unhashed(&mn->hlist)) {
 289                hlist_del_rcu(&mn->hlist);
 290
 291                /*
 292                 * RCU here will force exit_mmap to wait ->release to finish
 293                 * before freeing the pages.
 294                 */
 295                rcu_read_lock();
 296                spin_unlock(&mm->mmu_notifier_mm->lock);
 297                /*
 298                 * exit_mmap will block in mmu_notifier_release to
 299                 * guarantee ->release is called before freeing the
 300                 * pages.
 301                 */
 302                if (mn->ops->release)
 303                        mn->ops->release(mn, mm);
 304                rcu_read_unlock();
 305        } else
 306                spin_unlock(&mm->mmu_notifier_mm->lock);
 307
 308        /*
 309         * Wait any running method to finish, of course including
 310         * ->release if it was run by mmu_notifier_relase instead of us.
 311         */
 312        synchronize_rcu();
 313
 314        BUG_ON(atomic_read(&mm->mm_count) <= 0);
 315
 316        mmdrop(mm);
 317}
 318EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
 319
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