/*
* linux/mm/mmu_notifier.c
*
* Copyright (C) 2008 Qumranet, Inc.
* Copyright (C) 2008 SGI
* Christoph Lameter <cl@linux.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/sched/mm.h>
#include <linux/slab.h>
/* global SRCU for all MMs */
DEFINE_STATIC_SRCU(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);
/*
* 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 start,
unsigned long end)
{
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, start, end);
}
srcu_read_unlock(&srcu, id);
return young;
}
int __mmu_notifier_clear_young(struct mm_struct *mm,
unsigned long start,
unsigned long end)
{
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_young)
young |= mn->ops->clear_young(mn, mm, start, end);
}
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);
}
int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
{
struct mmu_notifier *mn;
int ret = 0;
int id;
id = srcu_read_lock(&srcu);
hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {
if (mn->ops->invalidate_range_start) {
int _ret = mn->ops->invalidate_range_start(mn, range);
if (_ret) {
pr_info("%pS callback failed with %d in %sblockable context.\n",
mn->ops->invalidate_range_start, _ret,
!range->blockable ? "non-" : "");
ret = _ret;
}
}
}
srcu_read_unlock(&srcu, id);
return ret;
}
EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
void __mmu_notifier_invalidate_range_end(struct mmu_notifier_range *range,
bool only_end)
{
struct mmu_notifier *mn;
int id;
id = srcu_read_lock(&srcu);
hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {
/*
* Call invalidate_range here too to avoid the need for the
* subsystem of having to register an invalidate_range_end
* call-back when there is invalidate_range already. Usually a
* subsystem registers either invalidate_range_start()/end() or
* invalidate_range(), so this will be no additional overhead
* (besides the pointer check).
*
* We skip call to invalidate_range() if we know it is safe ie
* call site use mmu_notifier_invalidate_range_only_end() which
* is safe to do when we know that a call to invalidate_range()
* already happen under page table lock.
*/
if (!only_end && mn->ops->invalidate_range)
mn->ops->invalidate_range(mn, range->mm,
range->start,
range->end);
if (mn->ops->invalidate_range_end)
mn->ops->invalidate_range_end(mn, range);
}
srcu_read_unlock(&srcu, id);
}
EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
void __mmu_notifier_invalidate_range(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)
mn->ops->invalidate_range(mn, mm, start, end);
}
srcu_read_unlock(&srcu, id);
}
EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
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_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;
}
mmgrab(mm);
/*
* 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);
