FreeBSD/Linux Kernel Cross Reference
sys/mm/mmu_notifier.c

     /*
      *  linux/mm/mmu_notifier.c
      *
      *  Copyright (C) 2008  Qumranet, Inc.
      *  Copyright (C) 2008  SGI
      *             Christoph Lameter <clameter@sgi.com>
      *
      *  This work is licensed under the terms of the GNU GPL, version 2. See
      *  the COPYING file in the top-level directory.
     */
    
    #include <linux/rculist.h>
    #include <linux/mmu_notifier.h>
    #include <linux/export.h>
    #include <linux/mm.h>
    #include <linux/err.h>
    #include <linux/srcu.h>
    #include <linux/rcupdate.h>
    #include <linux/sched.h>
    #include <linux/slab.h>
    
    /* global SRCU for all MMs */
    static struct srcu_struct srcu;
    
    /*
     * This function can't run concurrently against mmu_notifier_register
     * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
     * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
     * in parallel despite there being no task using this mm any more,
     * through the vmas outside of the exit_mmap context, such as with
     * vmtruncate. This serializes against mmu_notifier_unregister with
     * the mmu_notifier_mm->lock in addition to SRCU and it serializes
     * against the other mmu notifiers with SRCU. struct mmu_notifier_mm
     * can't go away from under us as exit_mmap holds an mm_count pin
     * itself.
     */
    void __mmu_notifier_release(struct mm_struct *mm)
    {
            struct mmu_notifier *mn;
            struct hlist_node *n;
            int id;
    
            /*
             * SRCU here will block mmu_notifier_unregister until
             * ->release returns.
             */
            id = srcu_read_lock(&srcu);
            hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist)
                    /*
                     * if ->release runs before mmu_notifier_unregister it
                     * must be handled as it's the only way for the driver
                     * to flush all existing sptes and stop the driver
                     * from establishing any more sptes before all the
                     * pages in the mm are freed.
                     */
                    if (mn->ops->release)
                            mn->ops->release(mn, mm);
            srcu_read_unlock(&srcu, id);
    
            spin_lock(&mm->mmu_notifier_mm->lock);
            while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
                    mn = hlist_entry(mm->mmu_notifier_mm->list.first,
                                     struct mmu_notifier,
                                     hlist);
                    /*
                     * We arrived before mmu_notifier_unregister so
                     * mmu_notifier_unregister will do nothing other than
                     * to wait ->release to finish and
                     * mmu_notifier_unregister to return.
                     */
                    hlist_del_init_rcu(&mn->hlist);
            }
            spin_unlock(&mm->mmu_notifier_mm->lock);
    
            /*
             * synchronize_srcu here prevents mmu_notifier_release to
             * return to exit_mmap (which would proceed freeing all pages
             * in the mm) until the ->release method returns, if it was
             * invoked by mmu_notifier_unregister.
             *
             * The mmu_notifier_mm can't go away from under us because one
             * mm_count is hold by exit_mmap.
             */
            synchronize_srcu(&srcu);
    }
    
    /*
     * If no young bitflag is supported by the hardware, ->clear_flush_young can
     * unmap the address and return 1 or 0 depending if the mapping previously
     * existed or not.
     */
    int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
                                            unsigned long address)
    {
            struct mmu_notifier *mn;
            struct hlist_node *n;
            int young = 0, id;
    
            id = srcu_read_lock(&srcu);
           hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
                   if (mn->ops->clear_flush_young)
                           young |= mn->ops->clear_flush_young(mn, mm, address);
           }
           srcu_read_unlock(&srcu, id);
   
           return young;
   }
   
   int __mmu_notifier_test_young(struct mm_struct *mm,
                                 unsigned long address)
   {
           struct mmu_notifier *mn;
           struct hlist_node *n;
           int young = 0, id;
   
           id = srcu_read_lock(&srcu);
           hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
                   if (mn->ops->test_young) {
                           young = mn->ops->test_young(mn, mm, address);
                           if (young)
                                   break;
                   }
           }
           srcu_read_unlock(&srcu, id);
   
           return young;
   }
   
   void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
                                  pte_t pte)
   {
           struct mmu_notifier *mn;
           struct hlist_node *n;
           int id;
   
           id = srcu_read_lock(&srcu);
           hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
                   if (mn->ops->change_pte)
                           mn->ops->change_pte(mn, mm, address, pte);
           }
           srcu_read_unlock(&srcu, id);
   }
   
   void __mmu_notifier_invalidate_page(struct mm_struct *mm,
                                             unsigned long address)
   {
           struct mmu_notifier *mn;
           struct hlist_node *n;
           int id;
   
           id = srcu_read_lock(&srcu);
           hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
                   if (mn->ops->invalidate_page)
                           mn->ops->invalidate_page(mn, mm, address);
           }
           srcu_read_unlock(&srcu, id);
   }
   
   void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
                                     unsigned long start, unsigned long end)
   {
           struct mmu_notifier *mn;
           struct hlist_node *n;
           int id;
   
           id = srcu_read_lock(&srcu);
           hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
                   if (mn->ops->invalidate_range_start)
                           mn->ops->invalidate_range_start(mn, mm, start, end);
           }
           srcu_read_unlock(&srcu, id);
   }
   
   void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
                                     unsigned long start, unsigned long end)
   {
           struct mmu_notifier *mn;
           struct hlist_node *n;
           int id;
   
           id = srcu_read_lock(&srcu);
           hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
                   if (mn->ops->invalidate_range_end)
                           mn->ops->invalidate_range_end(mn, mm, start, end);
           }
           srcu_read_unlock(&srcu, id);
   }
   
   static int do_mmu_notifier_register(struct mmu_notifier *mn,
                                       struct mm_struct *mm,
                                       int take_mmap_sem)
   {
           struct mmu_notifier_mm *mmu_notifier_mm;
           int ret;
   
           BUG_ON(atomic_read(&mm->mm_users) <= 0);
   
           /*
            * Verify that mmu_notifier_init() already run and the global srcu is
            * initialized.
            */
           BUG_ON(!srcu.per_cpu_ref);
   
           ret = -ENOMEM;
           mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
           if (unlikely(!mmu_notifier_mm))
                   goto out;
   
           if (take_mmap_sem)
                   down_write(&mm->mmap_sem);
           ret = mm_take_all_locks(mm);
           if (unlikely(ret))
                   goto out_clean;
   
           if (!mm_has_notifiers(mm)) {
                   INIT_HLIST_HEAD(&mmu_notifier_mm->list);
                   spin_lock_init(&mmu_notifier_mm->lock);
   
                   mm->mmu_notifier_mm = mmu_notifier_mm;
                   mmu_notifier_mm = NULL;
           }
           atomic_inc(&mm->mm_count);
   
           /*
            * Serialize the update against mmu_notifier_unregister. A
            * side note: mmu_notifier_release can't run concurrently with
            * us because we hold the mm_users pin (either implicitly as
            * current->mm or explicitly with get_task_mm() or similar).
            * We can't race against any other mmu notifier method either
            * thanks to mm_take_all_locks().
            */
           spin_lock(&mm->mmu_notifier_mm->lock);
           hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
           spin_unlock(&mm->mmu_notifier_mm->lock);
   
           mm_drop_all_locks(mm);
   out_clean:
           if (take_mmap_sem)
                   up_write(&mm->mmap_sem);
           kfree(mmu_notifier_mm);
   out:
           BUG_ON(atomic_read(&mm->mm_users) <= 0);
           return ret;
   }
   
   /*
    * Must not hold mmap_sem nor any other VM related lock when calling
    * this registration function. Must also ensure mm_users can't go down
    * to zero while this runs to avoid races with mmu_notifier_release,
    * so mm has to be current->mm or the mm should be pinned safely such
    * as with get_task_mm(). If the mm is not current->mm, the mm_users
    * pin should be released by calling mmput after mmu_notifier_register
    * returns. mmu_notifier_unregister must be always called to
    * unregister the notifier. mm_count is automatically pinned to allow
    * mmu_notifier_unregister to safely run at any time later, before or
    * after exit_mmap. ->release will always be called before exit_mmap
    * frees the pages.
    */
   int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
   {
           return do_mmu_notifier_register(mn, mm, 1);
   }
   EXPORT_SYMBOL_GPL(mmu_notifier_register);
   
   /*
    * Same as mmu_notifier_register but here the caller must hold the
    * mmap_sem in write mode.
    */
   int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
   {
           return do_mmu_notifier_register(mn, mm, 0);
   }
   EXPORT_SYMBOL_GPL(__mmu_notifier_register);
   
   /* this is called after the last mmu_notifier_unregister() returned */
   void __mmu_notifier_mm_destroy(struct mm_struct *mm)
   {
           BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
           kfree(mm->mmu_notifier_mm);
           mm->mmu_notifier_mm = LIST_POISON1; /* debug */
   }
   
   /*
    * This releases the mm_count pin automatically and frees the mm
    * structure if it was the last user of it. It serializes against
    * running mmu notifiers with SRCU and against mmu_notifier_unregister
    * with the unregister lock + SRCU. All sptes must be dropped before
    * calling mmu_notifier_unregister. ->release or any other notifier
    * method may be invoked concurrently with mmu_notifier_unregister,
    * and only after mmu_notifier_unregister returned we're guaranteed
    * that ->release or any other method can't run anymore.
    */
   void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
   {
           BUG_ON(atomic_read(&mm->mm_count) <= 0);
   
           if (!hlist_unhashed(&mn->hlist)) {
                   /*
                    * SRCU here will force exit_mmap to wait ->release to finish
                    * before freeing the pages.
                    */
                   int id;
   
                   id = srcu_read_lock(&srcu);
                   /*
                    * exit_mmap will block in mmu_notifier_release to
                    * guarantee ->release is called before freeing the
                    * pages.
                    */
                   if (mn->ops->release)
                           mn->ops->release(mn, mm);
                   srcu_read_unlock(&srcu, id);
   
                   spin_lock(&mm->mmu_notifier_mm->lock);
                   hlist_del_rcu(&mn->hlist);
                   spin_unlock(&mm->mmu_notifier_mm->lock);
           }
   
           /*
            * Wait any running method to finish, of course including
            * ->release if it was run by mmu_notifier_relase instead of us.
            */
           synchronize_srcu(&srcu);
   
           BUG_ON(atomic_read(&mm->mm_count) <= 0);
   
           mmdrop(mm);
   }
   EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
   
   static int __init mmu_notifier_init(void)
   {
           return init_srcu_struct(&srcu);
   }
   
   module_init(mmu_notifier_init);

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