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/*
* 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/rcupdate.h>
#include <linux/sched.h>
#include <linux/slab.h>

/*
* 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 RCU and it serializes
* against the other mmu notifiers with RCU. 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;

/*
* RCU here will block mmu_notifier_unregister until
* ->release returns.
*/
rcu_read_lock();
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);
rcu_read_unlock();

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_rcu 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_rcu();
}

/*
* 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;

rcu_read_lock();
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);
}
rcu_read_unlock();

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;

rcu_read_lock();
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;
}
}
rcu_read_unlock();

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;

rcu_read_lock();
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);
/*
* Some drivers don't have change_pte,
* so we must call invalidate_page in that case.
*/
else if (mn->ops->invalidate_page)
mn->ops->invalidate_page(mn, mm, address);
}
rcu_read_unlock();
}

void __mmu_notifier_invalidate_page(struct mm_struct *mm,
unsigned long address)
{
struct mmu_notifier *mn;
struct hlist_node *n;

rcu_read_lock();
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);
}
rcu_read_unlock();
}

void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
unsigned long start, unsigned long end)
{
struct mmu_notifier *mn;
struct hlist_node *n;

rcu_read_lock();
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);
}
rcu_read_unlock();
}

void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
unsigned long start, unsigned long end)
{
struct mmu_notifier *mn;
struct hlist_node *n;

rcu_read_lock();
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);
}
rcu_read_unlock();
}

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);

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_cleanup;

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_cleanup:
if (take_mmap_sem)
up_write(&mm->mmap_sem);
/* kfree() does nothing if mmu_notifier_mm is NULL */
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 RCU and against mmu_notifier_unregister
* with the unregister lock + RCU. 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)) {
/*
* RCU here will force exit_mmap to wait ->release to finish
* before freeing the pages.
*/
rcu_read_lock();

/*
* 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);
rcu_read_unlock();

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_rcu();

BUG_ON(atomic_read(&mm->mm_count) <= 0);

mmdrop(mm);
}
EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
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