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mmu_notifier.c
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mmu_notifier.c
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// SPDX-License-Identifier: GPL-2.0-only
/*
* linux/mm/mmu_notifier.c
*
* Copyright (C) 2008 Qumranet, Inc.
* Copyright (C) 2008 SGI
* Christoph Lameter <[email protected]>
*/
#include <linux/rculist.h>
#include <linux/mmu_notifier.h>
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/err.h>
#include <linux/interval_tree.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);
#ifdef CONFIG_LOCKDEP
struct lockdep_map __mmu_notifier_invalidate_range_start_map = {
.name = "mmu_notifier_invalidate_range_start"
};
#endif
/*
* The mmu_notifier_subscriptions structure is allocated and installed in
* mm->notifier_subscriptions inside the mm_take_all_locks() protected
* critical section and it's released only when mm_count reaches zero
* in mmdrop().
*/
struct mmu_notifier_subscriptions {
/* all mmu notifiers registered in this mm are queued in this list */
struct hlist_head list;
bool has_itree;
/* to serialize the list modifications and hlist_unhashed */
spinlock_t lock;
unsigned long invalidate_seq;
unsigned long active_invalidate_ranges;
struct rb_root_cached itree;
wait_queue_head_t wq;
struct hlist_head deferred_list;
};
/*
* This is a collision-retry read-side/write-side 'lock', a lot like a
* seqcount, however this allows multiple write-sides to hold it at
* once. Conceptually the write side is protecting the values of the PTEs in
* this mm, such that PTES cannot be read into SPTEs (shadow PTEs) while any
* writer exists.
*
* Note that the core mm creates nested invalidate_range_start()/end() regions
* within the same thread, and runs invalidate_range_start()/end() in parallel
* on multiple CPUs. This is designed to not reduce concurrency or block
* progress on the mm side.
*
* As a secondary function, holding the full write side also serves to prevent
* writers for the itree, this is an optimization to avoid extra locking
* during invalidate_range_start/end notifiers.
*
* The write side has two states, fully excluded:
* - mm->active_invalidate_ranges != 0
* - subscriptions->invalidate_seq & 1 == True (odd)
* - some range on the mm_struct is being invalidated
* - the itree is not allowed to change
*
* And partially excluded:
* - mm->active_invalidate_ranges != 0
* - subscriptions->invalidate_seq & 1 == False (even)
* - some range on the mm_struct is being invalidated
* - the itree is allowed to change
*
* Operations on notifier_subscriptions->invalidate_seq (under spinlock):
* seq |= 1 # Begin writing
* seq++ # Release the writing state
* seq & 1 # True if a writer exists
*
* The later state avoids some expensive work on inv_end in the common case of
* no mmu_interval_notifier monitoring the VA.
*/
static bool
mn_itree_is_invalidating(struct mmu_notifier_subscriptions *subscriptions)
{
lockdep_assert_held(&subscriptions->lock);
return subscriptions->invalidate_seq & 1;
}
static struct mmu_interval_notifier *
mn_itree_inv_start_range(struct mmu_notifier_subscriptions *subscriptions,
const struct mmu_notifier_range *range,
unsigned long *seq)
{
struct interval_tree_node *node;
struct mmu_interval_notifier *res = NULL;
spin_lock(&subscriptions->lock);
subscriptions->active_invalidate_ranges++;
node = interval_tree_iter_first(&subscriptions->itree, range->start,
range->end - 1);
if (node) {
subscriptions->invalidate_seq |= 1;
res = container_of(node, struct mmu_interval_notifier,
interval_tree);
}
*seq = subscriptions->invalidate_seq;
spin_unlock(&subscriptions->lock);
return res;
}
static struct mmu_interval_notifier *
mn_itree_inv_next(struct mmu_interval_notifier *interval_sub,
const struct mmu_notifier_range *range)
{
struct interval_tree_node *node;
node = interval_tree_iter_next(&interval_sub->interval_tree,
range->start, range->end - 1);
if (!node)
return NULL;
return container_of(node, struct mmu_interval_notifier, interval_tree);
}
static void mn_itree_inv_end(struct mmu_notifier_subscriptions *subscriptions)
{
struct mmu_interval_notifier *interval_sub;
struct hlist_node *next;
spin_lock(&subscriptions->lock);
if (--subscriptions->active_invalidate_ranges ||
!mn_itree_is_invalidating(subscriptions)) {
spin_unlock(&subscriptions->lock);
return;
}
/* Make invalidate_seq even */
subscriptions->invalidate_seq++;
/*
* The inv_end incorporates a deferred mechanism like rtnl_unlock().
* Adds and removes are queued until the final inv_end happens then
* they are progressed. This arrangement for tree updates is used to
* avoid using a blocking lock during invalidate_range_start.
*/
hlist_for_each_entry_safe(interval_sub, next,
&subscriptions->deferred_list,
deferred_item) {
if (RB_EMPTY_NODE(&interval_sub->interval_tree.rb))
interval_tree_insert(&interval_sub->interval_tree,
&subscriptions->itree);
else
interval_tree_remove(&interval_sub->interval_tree,
&subscriptions->itree);
hlist_del(&interval_sub->deferred_item);
}
spin_unlock(&subscriptions->lock);
wake_up_all(&subscriptions->wq);
}
/**
* mmu_interval_read_begin - Begin a read side critical section against a VA
* range
* @interval_sub: The interval subscription
*
* mmu_iterval_read_begin()/mmu_iterval_read_retry() implement a
* collision-retry scheme similar to seqcount for the VA range under
* subscription. If the mm invokes invalidation during the critical section
* then mmu_interval_read_retry() will return true.
*
* This is useful to obtain shadow PTEs where teardown or setup of the SPTEs
* require a blocking context. The critical region formed by this can sleep,
* and the required 'user_lock' can also be a sleeping lock.
*
* The caller is required to provide a 'user_lock' to serialize both teardown
* and setup.
*
* The return value should be passed to mmu_interval_read_retry().
*/
unsigned long
mmu_interval_read_begin(struct mmu_interval_notifier *interval_sub)
{
struct mmu_notifier_subscriptions *subscriptions =
interval_sub->mm->notifier_subscriptions;
unsigned long seq;
bool is_invalidating;
/*
* If the subscription has a different seq value under the user_lock
* than we started with then it has collided.
*
* If the subscription currently has the same seq value as the
* subscriptions seq, then it is currently between
* invalidate_start/end and is colliding.
*
* The locking looks broadly like this:
* mn_tree_invalidate_start(): mmu_interval_read_begin():
* spin_lock
* seq = READ_ONCE(interval_sub->invalidate_seq);
* seq == subs->invalidate_seq
* spin_unlock
* spin_lock
* seq = ++subscriptions->invalidate_seq
* spin_unlock
* op->invalidate_range():
* user_lock
* mmu_interval_set_seq()
* interval_sub->invalidate_seq = seq
* user_unlock
*
* [Required: mmu_interval_read_retry() == true]
*
* mn_itree_inv_end():
* spin_lock
* seq = ++subscriptions->invalidate_seq
* spin_unlock
*
* user_lock
* mmu_interval_read_retry():
* interval_sub->invalidate_seq != seq
* user_unlock
*
* Barriers are not needed here as any races here are closed by an
* eventual mmu_interval_read_retry(), which provides a barrier via the
* user_lock.
*/
spin_lock(&subscriptions->lock);
/* Pairs with the WRITE_ONCE in mmu_interval_set_seq() */
seq = READ_ONCE(interval_sub->invalidate_seq);
is_invalidating = seq == subscriptions->invalidate_seq;
spin_unlock(&subscriptions->lock);
/*
* interval_sub->invalidate_seq must always be set to an odd value via
* mmu_interval_set_seq() using the provided cur_seq from
* mn_itree_inv_start_range(). This ensures that if seq does wrap we
* will always clear the below sleep in some reasonable time as
* subscriptions->invalidate_seq is even in the idle state.
*/
lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
lock_map_release(&__mmu_notifier_invalidate_range_start_map);
if (is_invalidating)
wait_event(subscriptions->wq,
READ_ONCE(subscriptions->invalidate_seq) != seq);
/*
* Notice that mmu_interval_read_retry() can already be true at this
* point, avoiding loops here allows the caller to provide a global
* time bound.
*/
return seq;
}
EXPORT_SYMBOL_GPL(mmu_interval_read_begin);
static void mn_itree_release(struct mmu_notifier_subscriptions *subscriptions,
struct mm_struct *mm)
{
struct mmu_notifier_range range = {
.flags = MMU_NOTIFIER_RANGE_BLOCKABLE,
.event = MMU_NOTIFY_RELEASE,
.mm = mm,
.start = 0,
.end = ULONG_MAX,
};
struct mmu_interval_notifier *interval_sub;
unsigned long cur_seq;
bool ret;
for (interval_sub =
mn_itree_inv_start_range(subscriptions, &range, &cur_seq);
interval_sub;
interval_sub = mn_itree_inv_next(interval_sub, &range)) {
ret = interval_sub->ops->invalidate(interval_sub, &range,
cur_seq);
WARN_ON(!ret);
}
mn_itree_inv_end(subscriptions);
}
/*
* 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 notifier_subscriptions->lock in addition to SRCU and it serializes
* against the other mmu notifiers with SRCU. struct mmu_notifier_subscriptions
* can't go away from under us as exit_mmap holds an mm_count pin
* itself.
*/
static void mn_hlist_release(struct mmu_notifier_subscriptions *subscriptions,
struct mm_struct *mm)
{
struct mmu_notifier *subscription;
int id;
/*
* SRCU here will block mmu_notifier_unregister until
* ->release returns.
*/
id = srcu_read_lock(&srcu);
hlist_for_each_entry_rcu(subscription, &subscriptions->list, hlist,
srcu_read_lock_held(&srcu))
/*
* 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 (subscription->ops->release)
subscription->ops->release(subscription, mm);
spin_lock(&subscriptions->lock);
while (unlikely(!hlist_empty(&subscriptions->list))) {
subscription = hlist_entry(subscriptions->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(&subscription->hlist);
}
spin_unlock(&subscriptions->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 notifier_subscriptions can't go away from under us because
* one mm_count is held by exit_mmap.
*/
synchronize_srcu(&srcu);
}
void __mmu_notifier_release(struct mm_struct *mm)
{
struct mmu_notifier_subscriptions *subscriptions =
mm->notifier_subscriptions;
if (subscriptions->has_itree)
mn_itree_release(subscriptions, mm);
if (!hlist_empty(&subscriptions->list))
mn_hlist_release(subscriptions, mm);
}
/*
* 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 *subscription;
int young = 0, id;
id = srcu_read_lock(&srcu);
hlist_for_each_entry_rcu(subscription,
&mm->notifier_subscriptions->list, hlist,
srcu_read_lock_held(&srcu)) {
if (subscription->ops->clear_flush_young)
young |= subscription->ops->clear_flush_young(
subscription, 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 *subscription;
int young = 0, id;
id = srcu_read_lock(&srcu);
hlist_for_each_entry_rcu(subscription,
&mm->notifier_subscriptions->list, hlist,
srcu_read_lock_held(&srcu)) {
if (subscription->ops->clear_young)
young |= subscription->ops->clear_young(subscription,
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 *subscription;
int young = 0, id;
id = srcu_read_lock(&srcu);
hlist_for_each_entry_rcu(subscription,
&mm->notifier_subscriptions->list, hlist,
srcu_read_lock_held(&srcu)) {
if (subscription->ops->test_young) {
young = subscription->ops->test_young(subscription, 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 *subscription;
int id;
id = srcu_read_lock(&srcu);
hlist_for_each_entry_rcu(subscription,
&mm->notifier_subscriptions->list, hlist,
srcu_read_lock_held(&srcu)) {
if (subscription->ops->change_pte)
subscription->ops->change_pte(subscription, mm, address,
pte);
}
srcu_read_unlock(&srcu, id);
}
static int mn_itree_invalidate(struct mmu_notifier_subscriptions *subscriptions,
const struct mmu_notifier_range *range)
{
struct mmu_interval_notifier *interval_sub;
unsigned long cur_seq;
for (interval_sub =
mn_itree_inv_start_range(subscriptions, range, &cur_seq);
interval_sub;
interval_sub = mn_itree_inv_next(interval_sub, range)) {
bool ret;
ret = interval_sub->ops->invalidate(interval_sub, range,
cur_seq);
if (!ret) {
if (WARN_ON(mmu_notifier_range_blockable(range)))
continue;
goto out_would_block;
}
}
return 0;
out_would_block:
/*
* On -EAGAIN the non-blocking caller is not allowed to call
* invalidate_range_end()
*/
mn_itree_inv_end(subscriptions);
return -EAGAIN;
}
static int mn_hlist_invalidate_range_start(
struct mmu_notifier_subscriptions *subscriptions,
struct mmu_notifier_range *range)
{
struct mmu_notifier *subscription;
int ret = 0;
int id;
id = srcu_read_lock(&srcu);
hlist_for_each_entry_rcu(subscription, &subscriptions->list, hlist,
srcu_read_lock_held(&srcu)) {
const struct mmu_notifier_ops *ops = subscription->ops;
if (ops->invalidate_range_start) {
int _ret;
if (!mmu_notifier_range_blockable(range))
non_block_start();
_ret = ops->invalidate_range_start(subscription, range);
if (!mmu_notifier_range_blockable(range))
non_block_end();
if (_ret) {
pr_info("%pS callback failed with %d in %sblockable context.\n",
ops->invalidate_range_start, _ret,
!mmu_notifier_range_blockable(range) ?
"non-" :
"");
WARN_ON(mmu_notifier_range_blockable(range) ||
_ret != -EAGAIN);
ret = _ret;
}
}
}
srcu_read_unlock(&srcu, id);
return ret;
}
int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
{
struct mmu_notifier_subscriptions *subscriptions =
range->mm->notifier_subscriptions;
int ret;
if (subscriptions->has_itree) {
ret = mn_itree_invalidate(subscriptions, range);
if (ret)
return ret;
}
if (!hlist_empty(&subscriptions->list))
return mn_hlist_invalidate_range_start(subscriptions, range);
return 0;
}
static void
mn_hlist_invalidate_end(struct mmu_notifier_subscriptions *subscriptions,
struct mmu_notifier_range *range, bool only_end)
{
struct mmu_notifier *subscription;
int id;
id = srcu_read_lock(&srcu);
hlist_for_each_entry_rcu(subscription, &subscriptions->list, hlist,
srcu_read_lock_held(&srcu)) {
/*
* 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 && subscription->ops->invalidate_range)
subscription->ops->invalidate_range(subscription,
range->mm,
range->start,
range->end);
if (subscription->ops->invalidate_range_end) {
if (!mmu_notifier_range_blockable(range))
non_block_start();
subscription->ops->invalidate_range_end(subscription,
range);
if (!mmu_notifier_range_blockable(range))
non_block_end();
}
}
srcu_read_unlock(&srcu, id);
}
void __mmu_notifier_invalidate_range_end(struct mmu_notifier_range *range,
bool only_end)
{
struct mmu_notifier_subscriptions *subscriptions =
range->mm->notifier_subscriptions;
lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
if (subscriptions->has_itree)
mn_itree_inv_end(subscriptions);
if (!hlist_empty(&subscriptions->list))
mn_hlist_invalidate_end(subscriptions, range, only_end);
lock_map_release(&__mmu_notifier_invalidate_range_start_map);
}
void __mmu_notifier_invalidate_range(struct mm_struct *mm,
unsigned long start, unsigned long end)
{
struct mmu_notifier *subscription;
int id;
id = srcu_read_lock(&srcu);
hlist_for_each_entry_rcu(subscription,
&mm->notifier_subscriptions->list, hlist,
srcu_read_lock_held(&srcu)) {
if (subscription->ops->invalidate_range)
subscription->ops->invalidate_range(subscription, mm,
start, end);
}
srcu_read_unlock(&srcu, id);
}
/*
* Same as mmu_notifier_register but here the caller must hold the mmap_lock in
* write mode. A NULL mn signals the notifier is being registered for itree
* mode.
*/
int __mmu_notifier_register(struct mmu_notifier *subscription,
struct mm_struct *mm)
{
struct mmu_notifier_subscriptions *subscriptions = NULL;
int ret;
mmap_assert_write_locked(mm);
BUG_ON(atomic_read(&mm->mm_users) <= 0);
if (IS_ENABLED(CONFIG_LOCKDEP)) {
fs_reclaim_acquire(GFP_KERNEL);
lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
lock_map_release(&__mmu_notifier_invalidate_range_start_map);
fs_reclaim_release(GFP_KERNEL);
}
if (!mm->notifier_subscriptions) {
/*
* kmalloc cannot be called under mm_take_all_locks(), but we
* know that mm->notifier_subscriptions can't change while we
* hold the write side of the mmap_lock.
*/
subscriptions = kzalloc(
sizeof(struct mmu_notifier_subscriptions), GFP_KERNEL);
if (!subscriptions)
return -ENOMEM;
INIT_HLIST_HEAD(&subscriptions->list);
spin_lock_init(&subscriptions->lock);
subscriptions->invalidate_seq = 2;
subscriptions->itree = RB_ROOT_CACHED;
init_waitqueue_head(&subscriptions->wq);
INIT_HLIST_HEAD(&subscriptions->deferred_list);
}
ret = mm_take_all_locks(mm);
if (unlikely(ret))
goto out_clean;
/*
* 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().
*
* release semantics on the initialization of the
* mmu_notifier_subscriptions's contents are provided for unlocked
* readers. acquire can only be used while holding the mmgrab or
* mmget, and is safe because once created the
* mmu_notifier_subscriptions is not freed until the mm is destroyed.
* As above, users holding the mmap_lock or one of the
* mm_take_all_locks() do not need to use acquire semantics.
*/
if (subscriptions)
smp_store_release(&mm->notifier_subscriptions, subscriptions);
if (subscription) {
/* Pairs with the mmdrop in mmu_notifier_unregister_* */
mmgrab(mm);
subscription->mm = mm;
subscription->users = 1;
spin_lock(&mm->notifier_subscriptions->lock);
hlist_add_head_rcu(&subscription->hlist,
&mm->notifier_subscriptions->list);
spin_unlock(&mm->notifier_subscriptions->lock);
} else
mm->notifier_subscriptions->has_itree = true;
mm_drop_all_locks(mm);
BUG_ON(atomic_read(&mm->mm_users) <= 0);
return 0;
out_clean:
kfree(subscriptions);
return ret;
}
EXPORT_SYMBOL_GPL(__mmu_notifier_register);
/**
* mmu_notifier_register - Register a notifier on a mm
* @subscription: The notifier to attach
* @mm: The mm to attach the notifier to
*
* Must not hold mmap_lock 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() or mmu_notifier_put() must be always called to
* unregister the notifier.
*
* While the caller has a mmu_notifier get the subscription->mm pointer will remain
* valid, and can be converted to an active mm pointer via mmget_not_zero().
*/
int mmu_notifier_register(struct mmu_notifier *subscription,
struct mm_struct *mm)
{
int ret;
mmap_write_lock(mm);
ret = __mmu_notifier_register(subscription, mm);
mmap_write_unlock(mm);
return ret;
}
EXPORT_SYMBOL_GPL(mmu_notifier_register);
static struct mmu_notifier *
find_get_mmu_notifier(struct mm_struct *mm, const struct mmu_notifier_ops *ops)
{
struct mmu_notifier *subscription;
spin_lock(&mm->notifier_subscriptions->lock);
hlist_for_each_entry_rcu(subscription,
&mm->notifier_subscriptions->list, hlist,
lockdep_is_held(&mm->notifier_subscriptions->lock)) {
if (subscription->ops != ops)
continue;
if (likely(subscription->users != UINT_MAX))
subscription->users++;
else
subscription = ERR_PTR(-EOVERFLOW);
spin_unlock(&mm->notifier_subscriptions->lock);
return subscription;
}
spin_unlock(&mm->notifier_subscriptions->lock);
return NULL;
}
/**
* mmu_notifier_get_locked - Return the single struct mmu_notifier for
* the mm & ops
* @ops: The operations struct being subscribe with
* @mm : The mm to attach notifiers too
*
* This function either allocates a new mmu_notifier via
* ops->alloc_notifier(), or returns an already existing notifier on the
* list. The value of the ops pointer is used to determine when two notifiers
* are the same.
*
* Each call to mmu_notifier_get() must be paired with a call to
* mmu_notifier_put(). The caller must hold the write side of mm->mmap_lock.
*
* While the caller has a mmu_notifier get the mm pointer will remain valid,
* and can be converted to an active mm pointer via mmget_not_zero().
*/
struct mmu_notifier *mmu_notifier_get_locked(const struct mmu_notifier_ops *ops,
struct mm_struct *mm)
{
struct mmu_notifier *subscription;
int ret;
mmap_assert_write_locked(mm);
if (mm->notifier_subscriptions) {
subscription = find_get_mmu_notifier(mm, ops);
if (subscription)
return subscription;
}
subscription = ops->alloc_notifier(mm);
if (IS_ERR(subscription))
return subscription;
subscription->ops = ops;
ret = __mmu_notifier_register(subscription, mm);
if (ret)
goto out_free;
return subscription;
out_free:
subscription->ops->free_notifier(subscription);
return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(mmu_notifier_get_locked);
/* this is called after the last mmu_notifier_unregister() returned */
void __mmu_notifier_subscriptions_destroy(struct mm_struct *mm)
{
BUG_ON(!hlist_empty(&mm->notifier_subscriptions->list));
kfree(mm->notifier_subscriptions);
mm->notifier_subscriptions = 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 *subscription,
struct mm_struct *mm)
{
BUG_ON(atomic_read(&mm->mm_count) <= 0);
if (!hlist_unhashed(&subscription->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 (subscription->ops->release)
subscription->ops->release(subscription, mm);
srcu_read_unlock(&srcu, id);
spin_lock(&mm->notifier_subscriptions->lock);
/*
* Can not use list_del_rcu() since __mmu_notifier_release
* can delete it before we hold the lock.
*/
hlist_del_init_rcu(&subscription->hlist);
spin_unlock(&mm->notifier_subscriptions->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);
static void mmu_notifier_free_rcu(struct rcu_head *rcu)
{
struct mmu_notifier *subscription =
container_of(rcu, struct mmu_notifier, rcu);
struct mm_struct *mm = subscription->mm;
subscription->ops->free_notifier(subscription);
/* Pairs with the get in __mmu_notifier_register() */
mmdrop(mm);
}
/**
* mmu_notifier_put - Release the reference on the notifier
* @subscription: The notifier to act on
*
* This function must be paired with each mmu_notifier_get(), it releases the
* reference obtained by the get. If this is the last reference then process
* to free the notifier will be run asynchronously.
*
* Unlike mmu_notifier_unregister() the get/put flow only calls ops->release
* when the mm_struct is destroyed. Instead free_notifier is always called to
* release any resources held by the user.
*
* As ops->release is not guaranteed to be called, the user must ensure that
* all sptes are dropped, and no new sptes can be established before
* mmu_notifier_put() is called.
*
* This function can be called from the ops->release callback, however the
* caller must still ensure it is called pairwise with mmu_notifier_get().
*
* Modules calling this function must call mmu_notifier_synchronize() in
* their __exit functions to ensure the async work is completed.
*/
void mmu_notifier_put(struct mmu_notifier *subscription)
{
struct mm_struct *mm = subscription->mm;
spin_lock(&mm->notifier_subscriptions->lock);
if (WARN_ON(!subscription->users) || --subscription->users)
goto out_unlock;
hlist_del_init_rcu(&subscription->hlist);
spin_unlock(&mm->notifier_subscriptions->lock);
call_srcu(&srcu, &subscription->rcu, mmu_notifier_free_rcu);
return;
out_unlock:
spin_unlock(&mm->notifier_subscriptions->lock);
}
EXPORT_SYMBOL_GPL(mmu_notifier_put);
static int __mmu_interval_notifier_insert(
struct mmu_interval_notifier *interval_sub, struct mm_struct *mm,
struct mmu_notifier_subscriptions *subscriptions, unsigned long start,
unsigned long length, const struct mmu_interval_notifier_ops *ops)
{
interval_sub->mm = mm;
interval_sub->ops = ops;
RB_CLEAR_NODE(&interval_sub->interval_tree.rb);
interval_sub->interval_tree.start = start;
/*
* Note that the representation of the intervals in the interval tree
* considers the ending point as contained in the interval.
*/
if (length == 0 ||
check_add_overflow(start, length - 1,
&interval_sub->interval_tree.last))
return -EOVERFLOW;
/* Must call with a mmget() held */
if (WARN_ON(atomic_read(&mm->mm_users) <= 0))
return -EINVAL;
/* pairs with mmdrop in mmu_interval_notifier_remove() */
mmgrab(mm);
/*
* If some invalidate_range_start/end region is going on in parallel
* we don't know what VA ranges are affected, so we must assume this
* new range is included.
*
* If the itree is invalidating then we are not allowed to change
* it. Retrying until invalidation is done is tricky due to the
* possibility for live lock, instead defer the add to
* mn_itree_inv_end() so this algorithm is deterministic.
*
* In all cases the value for the interval_sub->invalidate_seq should be
* odd, see mmu_interval_read_begin()
*/
spin_lock(&subscriptions->lock);
if (subscriptions->active_invalidate_ranges) {
if (mn_itree_is_invalidating(subscriptions))
hlist_add_head(&interval_sub->deferred_item,
&subscriptions->deferred_list);
else {
subscriptions->invalidate_seq |= 1;
interval_tree_insert(&interval_sub->interval_tree,
&subscriptions->itree);
}
interval_sub->invalidate_seq = subscriptions->invalidate_seq;
} else {
WARN_ON(mn_itree_is_invalidating(subscriptions));
/*
* The starting seq for a subscription not under invalidation
* should be odd, not equal to the current invalidate_seq and
* invalidate_seq should not 'wrap' to the new seq any time
* soon.
*/
interval_sub->invalidate_seq =
subscriptions->invalidate_seq - 1;
interval_tree_insert(&interval_sub->interval_tree,
&subscriptions->itree);
}
spin_unlock(&subscriptions->lock);
return 0;
}
/**
* mmu_interval_notifier_insert - Insert an interval notifier
* @interval_sub: Interval subscription to register
* @start: Starting virtual address to monitor
* @length: Length of the range to monitor
* @mm: mm_struct to attach to
* @ops: Interval notifier operations to be called on matching events
*
* This function subscribes the interval notifier for notifications from the
* mm. Upon return the ops related to mmu_interval_notifier will be called
* whenever an event that intersects with the given range occurs.
*
* Upon return the range_notifier may not be present in the interval tree yet.
* The caller must use the normal interval notifier read flow via
* mmu_interval_read_begin() to establish SPTEs for this range.
*/
int mmu_interval_notifier_insert(struct mmu_interval_notifier *interval_sub,
struct mm_struct *mm, unsigned long start,
unsigned long length,
const struct mmu_interval_notifier_ops *ops)
{
struct mmu_notifier_subscriptions *subscriptions;
int ret;
might_lock(&mm->mmap_lock);
subscriptions = smp_load_acquire(&mm->notifier_subscriptions);
if (!subscriptions || !subscriptions->has_itree) {
ret = mmu_notifier_register(NULL, mm);
if (ret)
return ret;
subscriptions = mm->notifier_subscriptions;
}
return __mmu_interval_notifier_insert(interval_sub, mm, subscriptions,
start, length, ops);
}
EXPORT_SYMBOL_GPL(mmu_interval_notifier_insert);