linux/mm/mmu_notifier.c
<<
>>
Prefs
   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/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        struct hlist_node *n;
  37
  38        /*
  39         * RCU here will block mmu_notifier_unregister until
  40         * ->release returns.
  41         */
  42        rcu_read_lock();
  43        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist)
  44                /*
  45                 * if ->release runs before mmu_notifier_unregister it
  46                 * must be handled as it's the only way for the driver
  47                 * to flush all existing sptes and stop the driver
  48                 * from establishing any more sptes before all the
  49                 * pages in the mm are freed.
  50                 */
  51                if (mn->ops->release)
  52                        mn->ops->release(mn, mm);
  53        rcu_read_unlock();
  54
  55        spin_lock(&mm->mmu_notifier_mm->lock);
  56        while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
  57                mn = hlist_entry(mm->mmu_notifier_mm->list.first,
  58                                 struct mmu_notifier,
  59                                 hlist);
  60                /*
  61                 * We arrived before mmu_notifier_unregister so
  62                 * mmu_notifier_unregister will do nothing other than
  63                 * to wait ->release to finish and
  64                 * mmu_notifier_unregister to return.
  65                 */
  66                hlist_del_init_rcu(&mn->hlist);
  67        }
  68        spin_unlock(&mm->mmu_notifier_mm->lock);
  69
  70        /*
  71         * synchronize_rcu here prevents mmu_notifier_release to
  72         * return to exit_mmap (which would proceed freeing all pages
  73         * in the mm) until the ->release method returns, if it was
  74         * invoked by mmu_notifier_unregister.
  75         *
  76         * The mmu_notifier_mm can't go away from under us because one
  77         * mm_count is hold by exit_mmap.
  78         */
  79        synchronize_rcu();
  80}
  81
  82/*
  83 * If no young bitflag is supported by the hardware, ->clear_flush_young can
  84 * unmap the address and return 1 or 0 depending if the mapping previously
  85 * existed or not.
  86 */
  87int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
  88                                        unsigned long address)
  89{
  90        struct mmu_notifier *mn;
  91        struct hlist_node *n;
  92        int young = 0;
  93
  94        rcu_read_lock();
  95        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
  96                if (mn->ops->clear_flush_young)
  97                        young |= mn->ops->clear_flush_young(mn, mm, address);
  98        }
  99        rcu_read_unlock();
 100
 101        return young;
 102}
 103
 104int __mmu_notifier_test_young(struct mm_struct *mm,
 105                              unsigned long address)
 106{
 107        struct mmu_notifier *mn;
 108        struct hlist_node *n;
 109        int young = 0;
 110
 111        rcu_read_lock();
 112        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
 113                if (mn->ops->test_young) {
 114                        young = mn->ops->test_young(mn, mm, address);
 115                        if (young)
 116                                break;
 117                }
 118        }
 119        rcu_read_unlock();
 120
 121        return young;
 122}
 123
 124void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
 125                               pte_t pte)
 126{
 127        struct mmu_notifier *mn;
 128        struct hlist_node *n;
 129
 130        rcu_read_lock();
 131        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
 132                if (mn->ops->change_pte)
 133                        mn->ops->change_pte(mn, mm, address, pte);
 134                /*
 135                 * Some drivers don't have change_pte,
 136                 * so we must call invalidate_page in that case.
 137                 */
 138                else if (mn->ops->invalidate_page)
 139                        mn->ops->invalidate_page(mn, mm, address);
 140        }
 141        rcu_read_unlock();
 142}
 143
 144void __mmu_notifier_invalidate_page(struct mm_struct *mm,
 145                                          unsigned long address)
 146{
 147        struct mmu_notifier *mn;
 148        struct hlist_node *n;
 149
 150        rcu_read_lock();
 151        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
 152                if (mn->ops->invalidate_page)
 153                        mn->ops->invalidate_page(mn, mm, address);
 154        }
 155        rcu_read_unlock();
 156}
 157
 158void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
 159                                  unsigned long start, unsigned long end)
 160{
 161        struct mmu_notifier *mn;
 162        struct hlist_node *n;
 163
 164        rcu_read_lock();
 165        hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
 166                if (mn->ops->invalidate_range_start)
 167                        mn->ops->invalidate_range_start(mn, mm, start, end);
 168        }
 169        rcu_read_unlock();
 170}
 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        struct hlist_node *n;
 177
 178        rcu_read_lock();
 179        hlist_for_each_entry_rcu(mn, n, &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        rcu_read_unlock();
 184}
 185
 186static int do_mmu_notifier_register(struct mmu_notifier *mn,
 187                                    struct mm_struct *mm,
 188                                    int take_mmap_sem)
 189{
 190        struct mmu_notifier_mm *mmu_notifier_mm;
 191        int ret;
 192
 193        BUG_ON(atomic_read(&mm->mm_users) <= 0);
 194
 195        ret = -ENOMEM;
 196        mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
 197        if (unlikely(!mmu_notifier_mm))
 198                goto out;
 199
 200        if (take_mmap_sem)
 201                down_write(&mm->mmap_sem);
 202        ret = mm_take_all_locks(mm);
 203        if (unlikely(ret))
 204                goto out_cleanup;
 205
 206        if (!mm_has_notifiers(mm)) {
 207                INIT_HLIST_HEAD(&mmu_notifier_mm->list);
 208                spin_lock_init(&mmu_notifier_mm->lock);
 209                mm->mmu_notifier_mm = mmu_notifier_mm;
 210                mmu_notifier_mm = NULL;
 211        }
 212        atomic_inc(&mm->mm_count);
 213
 214        /*
 215         * Serialize the update against mmu_notifier_unregister. A
 216         * side note: mmu_notifier_release can't run concurrently with
 217         * us because we hold the mm_users pin (either implicitly as
 218         * current->mm or explicitly with get_task_mm() or similar).
 219         * We can't race against any other mmu notifier method either
 220         * thanks to mm_take_all_locks().
 221         */
 222        spin_lock(&mm->mmu_notifier_mm->lock);
 223        hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
 224        spin_unlock(&mm->mmu_notifier_mm->lock);
 225
 226        mm_drop_all_locks(mm);
 227out_cleanup:
 228        if (take_mmap_sem)
 229                up_write(&mm->mmap_sem);
 230        /* kfree() does nothing if mmu_notifier_mm is NULL */
 231        kfree(mmu_notifier_mm);
 232out:
 233        BUG_ON(atomic_read(&mm->mm_users) <= 0);
 234        return ret;
 235}
 236
 237/*
 238 * Must not hold mmap_sem nor any other VM related lock when calling
 239 * this registration function. Must also ensure mm_users can't go down
 240 * to zero while this runs to avoid races with mmu_notifier_release,
 241 * so mm has to be current->mm or the mm should be pinned safely such
 242 * as with get_task_mm(). If the mm is not current->mm, the mm_users
 243 * pin should be released by calling mmput after mmu_notifier_register
 244 * returns. mmu_notifier_unregister must be always called to
 245 * unregister the notifier. mm_count is automatically pinned to allow
 246 * mmu_notifier_unregister to safely run at any time later, before or
 247 * after exit_mmap. ->release will always be called before exit_mmap
 248 * frees the pages.
 249 */
 250int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 251{
 252        return do_mmu_notifier_register(mn, mm, 1);
 253}
 254EXPORT_SYMBOL_GPL(mmu_notifier_register);
 255
 256/*
 257 * Same as mmu_notifier_register but here the caller must hold the
 258 * mmap_sem in write mode.
 259 */
 260int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 261{
 262        return do_mmu_notifier_register(mn, mm, 0);
 263}
 264EXPORT_SYMBOL_GPL(__mmu_notifier_register);
 265
 266/* this is called after the last mmu_notifier_unregister() returned */
 267void __mmu_notifier_mm_destroy(struct mm_struct *mm)
 268{
 269        BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
 270        kfree(mm->mmu_notifier_mm);
 271        mm->mmu_notifier_mm = LIST_POISON1; /* debug */
 272}
 273
 274/*
 275 * This releases the mm_count pin automatically and frees the mm
 276 * structure if it was the last user of it. It serializes against
 277 * running mmu notifiers with RCU and against mmu_notifier_unregister
 278 * with the unregister lock + RCU. All sptes must be dropped before
 279 * calling mmu_notifier_unregister. ->release or any other notifier
 280 * method may be invoked concurrently with mmu_notifier_unregister,
 281 * and only after mmu_notifier_unregister returned we're guaranteed
 282 * that ->release or any other method can't run anymore.
 283 */
 284void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
 285{
 286        BUG_ON(atomic_read(&mm->mm_count) <= 0);
 287
 288        if (!hlist_unhashed(&mn->hlist)) {
 289                /*
 290                 * RCU here will force exit_mmap to wait ->release to finish
 291                 * before freeing the pages.
 292                 */
 293                rcu_read_lock();
 294
 295                /*
 296                 * exit_mmap will block in mmu_notifier_release to
 297                 * guarantee ->release is called before freeing the
 298                 * pages.
 299                 */
 300                if (mn->ops->release)
 301                        mn->ops->release(mn, mm);
 302                rcu_read_unlock();
 303
 304                spin_lock(&mm->mmu_notifier_mm->lock);
 305                hlist_del_rcu(&mn->hlist);
 306                spin_unlock(&mm->mmu_notifier_mm->lock);
 307        }
 308
 309        /*
 310         * Wait any running method to finish, of course including
 311         * ->release if it was run by mmu_notifier_relase instead of us.
 312         */
 313        synchronize_rcu();
 314
 315        BUG_ON(atomic_read(&mm->mm_count) <= 0);
 316
 317        mmdrop(mm);
 318}
 319EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
 320
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.