mmu_notifier.c

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/*
 *  linux/mm/mmu_notifier.c
 *
 *  Copyright (C) 2008  Qumranet, Inc.
 *  Copyright (C) 2008  SGI
 *             Christoph Lameter <[email protected]>
 *
 *  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);