[deliverable/linux.git] / 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 allows mmu_notifier::release callback to delay a call to
 * a function that will free appropriate resources. The function must be
 * quick and must not block.
 */
void mmu_notifier_call_srcu(struct rcu_head *rcu,
			    void (*func)(struct rcu_head *rcu))
{
	call_srcu(&srcu, rcu, func);
}
EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu);

void mmu_notifier_synchronize(void)
{
	/* Wait for any running method to finish. */
	srcu_barrier(&srcu);
}
EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);

/*
 * 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;
	int id;

	/*
	 * SRCU here will block mmu_notifier_unregister until
	 * ->release returns.
	 */
	id = srcu_read_lock(&srcu);
	hlist_for_each_entry_rcu(mn, &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);

	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
		 * for ->release to finish and for mmu_notifier_unregister to
		 * return.
		 */
		hlist_del_init_rcu(&mn->hlist);
	}
	spin_unlock(&mm->mmu_notifier_mm->lock);
	srcu_read_unlock(&srcu, id);

	/*
	 * synchronize_srcu here prevents mmu_notifier_release from returning to
	 * exit_mmap (which would proceed with 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 held 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;
	int young = 0, id;

	id = srcu_read_lock(&srcu);
	hlist_for_each_entry_rcu(mn, &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;
	int young = 0, id;

	id = srcu_read_lock(&srcu);
	hlist_for_each_entry_rcu(mn, &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;
	int id;

	id = srcu_read_lock(&srcu);
	hlist_for_each_entry_rcu(mn, &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;
	int id;

	id = srcu_read_lock(&srcu);
	hlist_for_each_entry_rcu(mn, &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;
	int id;

	id = srcu_read_lock(&srcu);
	hlist_for_each_entry_rcu(mn, &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);
}
EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);

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

	id = srcu_read_lock(&srcu);
	hlist_for_each_entry_rcu(mn, &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);
}
EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);

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 for ->release to
		 * finish before freeing the pages.
		 */
		int id;

		id = srcu_read_lock(&srcu);
		/*
		 * exit_mmap will block in mmu_notifier_release to guarantee
		 * that ->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);
		/*
		 * Can not use list_del_rcu() since __mmu_notifier_release
		 * can delete it before we hold the lock.
		 */
		hlist_del_init_rcu(&mn->hlist);
		spin_unlock(&mm->mmu_notifier_mm->lock);
	}

	/*
	 * Wait for any running method to finish, of course including
	 * ->release if it was run by mmu_notifier_release instead of us.
	 */
	synchronize_srcu(&srcu);

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

	mmdrop(mm);
}
EXPORT_SYMBOL_GPL(mmu_notifier_unregister);

/*
 * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
 */
void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
					struct mm_struct *mm)
{
	spin_lock(&mm->mmu_notifier_mm->lock);
	/*
	 * Can not use list_del_rcu() since __mmu_notifier_release
	 * can delete it before we hold the lock.
	 */
	hlist_del_init_rcu(&mn->hlist);
	spin_unlock(&mm->mmu_notifier_mm->lock);

	BUG_ON(atomic_read(&mm->mm_count) <= 0);
	mmdrop(mm);
}
EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);

static int __init mmu_notifier_init(void)
{
	return init_srcu_struct(&srcu);
}
subsys_initcall(mmu_notifier_init);
Commit	Line	Data
cddb8a5c AA	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>
b95f1b31	14	#include <linux/export.h>
cddb8a5c AA	15	#include <linux/mm.h>
cddb8a5c AA	16	#include <linux/err.h>
21a92735	17	#include <linux/srcu.h>
cddb8a5c AA	18	#include <linux/rcupdate.h>
cddb8a5c AA	19	#include <linux/sched.h>
5a0e3ad6	20	#include <linux/slab.h>
cddb8a5c	21
21a92735	22	/* global SRCU for all MMs */
70400303	23	static struct srcu_struct srcu;
21a92735	24
b972216e PZ	25	/*
	26	* This function allows mmu_notifier::release callback to delay a call to
	27	* a function that will free appropriate resources. The function must be
	28	* quick and must not block.
	29	*/
	30	void mmu_notifier_call_srcu(struct rcu_head *rcu,
	31	void (func)(struct rcu_head rcu))
	32	{
	33	call_srcu(&srcu, rcu, func);
	34	}
	35	EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu);
	36
	37	void mmu_notifier_synchronize(void)
	38	{
	39	/* Wait for any running method to finish. */
	40	srcu_barrier(&srcu);
	41	}
	42	EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
	43
cddb8a5c AA	44	/*
	45	* This function can't run concurrently against mmu_notifier_register
	46	* because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
	47	* runs with mm_users == 0. Other tasks may still invoke mmu notifiers
	48	* in parallel despite there being no task using this mm any more,
	49	* through the vmas outside of the exit_mmap context, such as with
	50	* vmtruncate. This serializes against mmu_notifier_unregister with
21a92735 SG	51	* the mmu_notifier_mm->lock in addition to SRCU and it serializes
21a92735 SG	52	* against the other mmu notifiers with SRCU. struct mmu_notifier_mm
cddb8a5c AA	53	* can't go away from under us as exit_mmap holds an mm_count pin
	54	* itself.
	55	*/
	56	void __mmu_notifier_release(struct mm_struct *mm)
	57	{
	58	struct mmu_notifier *mn;
21a92735	59	int id;
3ad3d901 XG	60
3ad3d901 XG	61	/*
d34883d4 XG	62	* SRCU here will block mmu_notifier_unregister until
d34883d4 XG	63	* ->release returns.
3ad3d901	64	*/
21a92735	65	id = srcu_read_lock(&srcu);
d34883d4 XG	66	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
	67	/*
	68	* If ->release runs before mmu_notifier_unregister it must be
	69	* handled, as it's the only way for the driver to flush all
	70	* existing sptes and stop the driver from establishing any more
	71	* sptes before all the pages in the mm are freed.
	72	*/
	73	if (mn->ops->release)
	74	mn->ops->release(mn, mm);
d34883d4	75
cddb8a5c AA	76	spin_lock(&mm->mmu_notifier_mm->lock);
	77	while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
	78	mn = hlist_entry(mm->mmu_notifier_mm->list.first,
	79	struct mmu_notifier,
	80	hlist);
	81	/*
d34883d4 XG	82	* We arrived before mmu_notifier_unregister so
	83	* mmu_notifier_unregister will do nothing other than to wait
	84	* for ->release to finish and for mmu_notifier_unregister to
	85	* return.
cddb8a5c AA	86	*/
cddb8a5c AA	87	hlist_del_init_rcu(&mn->hlist);
cddb8a5c AA	88	}
cddb8a5c AA	89	spin_unlock(&mm->mmu_notifier_mm->lock);
b972216e	90	srcu_read_unlock(&srcu, id);
cddb8a5c AA	91
cddb8a5c AA	92	/*
d34883d4 XG	93	* synchronize_srcu here prevents mmu_notifier_release from returning to
	94	* exit_mmap (which would proceed with freeing all pages in the mm)
	95	* until the ->release method returns, if it was invoked by
	96	* mmu_notifier_unregister.
	97	*
	98	* The mmu_notifier_mm can't go away from under us because one mm_count
	99	* is held by exit_mmap.
cddb8a5c	100	*/
21a92735	101	synchronize_srcu(&srcu);
cddb8a5c AA	102	}
	103
	104	/*
	105	* If no young bitflag is supported by the hardware, ->clear_flush_young can
	106	* unmap the address and return 1 or 0 depending if the mapping previously
	107	* existed or not.
	108	*/
	109	int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
	110	unsigned long address)
	111	{
	112	struct mmu_notifier *mn;
21a92735	113	int young = 0, id;
cddb8a5c	114
21a92735	115	id = srcu_read_lock(&srcu);
b67bfe0d	116	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
cddb8a5c AA	117	if (mn->ops->clear_flush_young)
	118	young \|= mn->ops->clear_flush_young(mn, mm, address);
	119	}
21a92735	120	srcu_read_unlock(&srcu, id);
cddb8a5c AA	121
	122	return young;
	123	}
	124
8ee53820 AA	125	int __mmu_notifier_test_young(struct mm_struct *mm,
	126	unsigned long address)
	127	{
	128	struct mmu_notifier *mn;
21a92735	129	int young = 0, id;
8ee53820	130
21a92735	131	id = srcu_read_lock(&srcu);
b67bfe0d	132	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
8ee53820 AA	133	if (mn->ops->test_young) {
	134	young = mn->ops->test_young(mn, mm, address);
	135	if (young)
	136	break;
	137	}
	138	}
21a92735	139	srcu_read_unlock(&srcu, id);
8ee53820 AA	140
	141	return young;
	142	}
	143
828502d3 IE	144	void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
	145	pte_t pte)
	146	{
	147	struct mmu_notifier *mn;
21a92735	148	int id;
828502d3	149
21a92735	150	id = srcu_read_lock(&srcu);
b67bfe0d	151	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
828502d3 IE	152	if (mn->ops->change_pte)
828502d3 IE	153	mn->ops->change_pte(mn, mm, address, pte);
828502d3	154	}
21a92735	155	srcu_read_unlock(&srcu, id);
828502d3 IE	156	}
828502d3 IE	157
cddb8a5c AA	158	void __mmu_notifier_invalidate_page(struct mm_struct *mm,
	159	unsigned long address)
	160	{
	161	struct mmu_notifier *mn;
21a92735	162	int id;
cddb8a5c	163
21a92735	164	id = srcu_read_lock(&srcu);
b67bfe0d	165	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
cddb8a5c AA	166	if (mn->ops->invalidate_page)
	167	mn->ops->invalidate_page(mn, mm, address);
	168	}
21a92735	169	srcu_read_unlock(&srcu, id);
cddb8a5c AA	170	}
	171
	172	void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
	173	unsigned long start, unsigned long end)
	174	{
	175	struct mmu_notifier *mn;
21a92735	176	int id;
cddb8a5c	177
21a92735	178	id = srcu_read_lock(&srcu);
b67bfe0d	179	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
cddb8a5c AA	180	if (mn->ops->invalidate_range_start)
	181	mn->ops->invalidate_range_start(mn, mm, start, end);
	182	}
21a92735	183	srcu_read_unlock(&srcu, id);
cddb8a5c	184	}
fa794199	185	EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
cddb8a5c AA	186
	187	void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
	188	unsigned long start, unsigned long end)
	189	{
	190	struct mmu_notifier *mn;
21a92735	191	int id;
cddb8a5c	192
21a92735	193	id = srcu_read_lock(&srcu);
b67bfe0d	194	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
cddb8a5c AA	195	if (mn->ops->invalidate_range_end)
	196	mn->ops->invalidate_range_end(mn, mm, start, end);
	197	}
21a92735	198	srcu_read_unlock(&srcu, id);
cddb8a5c	199	}
fa794199	200	EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
cddb8a5c AA	201
	202	static int do_mmu_notifier_register(struct mmu_notifier *mn,
	203	struct mm_struct *mm,
	204	int take_mmap_sem)
	205	{
	206	struct mmu_notifier_mm *mmu_notifier_mm;
	207	int ret;
	208
	209	BUG_ON(atomic_read(&mm->mm_users) <= 0);
	210
21a92735	211	/*
35cfa2b0 GS	212	* Verify that mmu_notifier_init() already run and the global srcu is
	213	* initialized.
	214	*/
21a92735 SG	215	BUG_ON(!srcu.per_cpu_ref);
21a92735 SG	216
35cfa2b0 GS	217	ret = -ENOMEM;
	218	mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
	219	if (unlikely(!mmu_notifier_mm))
	220	goto out;
	221
cddb8a5c AA	222	if (take_mmap_sem)
	223	down_write(&mm->mmap_sem);
	224	ret = mm_take_all_locks(mm);
	225	if (unlikely(ret))
35cfa2b0	226	goto out_clean;
cddb8a5c AA	227
	228	if (!mm_has_notifiers(mm)) {
	229	INIT_HLIST_HEAD(&mmu_notifier_mm->list);
	230	spin_lock_init(&mmu_notifier_mm->lock);
e0f3c3f7	231
cddb8a5c	232	mm->mmu_notifier_mm = mmu_notifier_mm;
35cfa2b0	233	mmu_notifier_mm = NULL;
cddb8a5c AA	234	}
	235	atomic_inc(&mm->mm_count);
	236
	237	/*
	238	* Serialize the update against mmu_notifier_unregister. A
	239	* side note: mmu_notifier_release can't run concurrently with
	240	* us because we hold the mm_users pin (either implicitly as
	241	* current->mm or explicitly with get_task_mm() or similar).
	242	* We can't race against any other mmu notifier method either
	243	* thanks to mm_take_all_locks().
	244	*/
	245	spin_lock(&mm->mmu_notifier_mm->lock);
	246	hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
	247	spin_unlock(&mm->mmu_notifier_mm->lock);
	248
	249	mm_drop_all_locks(mm);
35cfa2b0	250	out_clean:
cddb8a5c AA	251	if (take_mmap_sem)
cddb8a5c AA	252	up_write(&mm->mmap_sem);
35cfa2b0 GS	253	kfree(mmu_notifier_mm);
35cfa2b0 GS	254	out:
cddb8a5c AA	255	BUG_ON(atomic_read(&mm->mm_users) <= 0);
	256	return ret;
	257	}
	258
	259	/*
	260	* Must not hold mmap_sem nor any other VM related lock when calling
	261	* this registration function. Must also ensure mm_users can't go down
	262	* to zero while this runs to avoid races with mmu_notifier_release,
	263	* so mm has to be current->mm or the mm should be pinned safely such
	264	* as with get_task_mm(). If the mm is not current->mm, the mm_users
	265	* pin should be released by calling mmput after mmu_notifier_register
	266	* returns. mmu_notifier_unregister must be always called to
	267	* unregister the notifier. mm_count is automatically pinned to allow
	268	* mmu_notifier_unregister to safely run at any time later, before or
	269	* after exit_mmap. ->release will always be called before exit_mmap
	270	* frees the pages.
	271	*/
	272	int mmu_notifier_register(struct mmu_notifier mn, struct mm_struct mm)
	273	{
	274	return do_mmu_notifier_register(mn, mm, 1);
	275	}
	276	EXPORT_SYMBOL_GPL(mmu_notifier_register);
	277
	278	/*
	279	* Same as mmu_notifier_register but here the caller must hold the
	280	* mmap_sem in write mode.
	281	*/
	282	int __mmu_notifier_register(struct mmu_notifier mn, struct mm_struct mm)
	283	{
	284	return do_mmu_notifier_register(mn, mm, 0);
	285	}
	286	EXPORT_SYMBOL_GPL(__mmu_notifier_register);
	287
	288	/* this is called after the last mmu_notifier_unregister() returned */
	289	void __mmu_notifier_mm_destroy(struct mm_struct *mm)
	290	{
	291	BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
	292	kfree(mm->mmu_notifier_mm);
	293	mm->mmu_notifier_mm = LIST_POISON1; /* debug */
	294	}
	295
	296	/*
	297	* This releases the mm_count pin automatically and frees the mm
	298	* structure if it was the last user of it. It serializes against
21a92735 SG	299	* running mmu notifiers with SRCU and against mmu_notifier_unregister
21a92735 SG	300	* with the unregister lock + SRCU. All sptes must be dropped before
cddb8a5c AA	301	* calling mmu_notifier_unregister. ->release or any other notifier
	302	* method may be invoked concurrently with mmu_notifier_unregister,
	303	* and only after mmu_notifier_unregister returned we're guaranteed
	304	* that ->release or any other method can't run anymore.
	305	*/
	306	void mmu_notifier_unregister(struct mmu_notifier mn, struct mm_struct mm)
	307	{
	308	BUG_ON(atomic_read(&mm->mm_count) <= 0);
	309
cddb8a5c	310	if (!hlist_unhashed(&mn->hlist)) {
d34883d4 XG	311	/*
	312	* SRCU here will force exit_mmap to wait for ->release to
	313	* finish before freeing the pages.
	314	*/
21a92735	315	int id;
3ad3d901	316
d34883d4	317	id = srcu_read_lock(&srcu);
cddb8a5c	318	/*
d34883d4 XG	319	* exit_mmap will block in mmu_notifier_release to guarantee
d34883d4 XG	320	* that ->release is called before freeing the pages.
cddb8a5c AA	321	*/
	322	if (mn->ops->release)
	323	mn->ops->release(mn, mm);
d34883d4	324	srcu_read_unlock(&srcu, id);
3ad3d901	325
d34883d4	326	spin_lock(&mm->mmu_notifier_mm->lock);
751efd86	327	/*
d34883d4 XG	328	* Can not use list_del_rcu() since __mmu_notifier_release
d34883d4 XG	329	* can delete it before we hold the lock.
751efd86	330	*/
d34883d4	331	hlist_del_init_rcu(&mn->hlist);
cddb8a5c	332	spin_unlock(&mm->mmu_notifier_mm->lock);
d34883d4	333	}
cddb8a5c AA	334
cddb8a5c AA	335	/*
d34883d4	336	* Wait for any running method to finish, of course including
83a35e36	337	* ->release if it was run by mmu_notifier_release instead of us.
cddb8a5c	338	*/
21a92735	339	synchronize_srcu(&srcu);
cddb8a5c AA	340
	341	BUG_ON(atomic_read(&mm->mm_count) <= 0);
	342
	343	mmdrop(mm);
	344	}
	345	EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
21a92735	346
b972216e PZ	347	/*
	348	* Same as mmu_notifier_unregister but no callback and no srcu synchronization.
	349	*/
	350	void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
	351	struct mm_struct *mm)
	352	{
	353	spin_lock(&mm->mmu_notifier_mm->lock);
	354	/*
	355	* Can not use list_del_rcu() since __mmu_notifier_release
	356	* can delete it before we hold the lock.
	357	*/
	358	hlist_del_init_rcu(&mn->hlist);
	359	spin_unlock(&mm->mmu_notifier_mm->lock);
	360
	361	BUG_ON(atomic_read(&mm->mm_count) <= 0);
	362	mmdrop(mm);
	363	}
	364	EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
	365
21a92735 SG	366	static int __init mmu_notifier_init(void)
	367	{
	368	return init_srcu_struct(&srcu);
	369	}
a64fb3cd	370	subsys_initcall(mmu_notifier_init);