Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1132 insertions, 0 deletions

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
new file mode 100644
index 000000000..f45ff1b76
--- /dev/null
+++ b/mm/mmu_notifier.c
@@ -0,0 +1,1132 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/mm/mmu_notifier.c
+ *
+ *  Copyright (C) 2008  Qumranet, Inc.
+ *  Copyright (C) 2008  SGI
+ *             Christoph Lameter <cl@linux.com>
+ */
+
+#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);
+				/*
+				 * We call all the notifiers on any EAGAIN,
+				 * there is no way for a notifier to know if
+				 * its start method failed, thus a start that
+				 * does EAGAIN can't also do end.
+				 */
+				WARN_ON(ops->invalidate_range_end);
+				ret = _ret;
+			}
+		}
+	}
+
+	if (ret) {
+		/*
+		 * Must be non-blocking to get here.  If there are multiple
+		 * notifiers and one or more failed start, any that succeeded
+		 * start are expecting their end to be called.  Do so now.
+		 */
+		hlist_for_each_entry_rcu(subscription, &subscriptions->list,
+					 hlist, srcu_read_lock_held(&srcu)) {
+			if (!subscription->ops->invalidate_range_end)
+				continue;
+
+			subscription->ops->invalidate_range_end(subscription,
+								range);
+		}
+	}
+	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 (!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);
+
+int mmu_interval_notifier_insert_locked(
+	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 =
+		mm->notifier_subscriptions;
+	int ret;
+
+	mmap_assert_write_locked(mm);
+
+	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_locked);
+
+static bool
+mmu_interval_seq_released(struct mmu_notifier_subscriptions *subscriptions,
+			  unsigned long seq)
+{
+	bool ret;
+
+	spin_lock(&subscriptions->lock);
+	ret = subscriptions->invalidate_seq != seq;
+	spin_unlock(&subscriptions->lock);
+	return ret;
+}
+
+/**
+ * mmu_interval_notifier_remove - Remove a interval notifier
+ * @interval_sub: Interval subscription to unregister
+ *
+ * This function must be paired with mmu_interval_notifier_insert(). It cannot
+ * be called from any ops callback.
+ *
+ * Once this returns ops callbacks are no longer running on other CPUs and
+ * will not be called in future.
+ */
+void mmu_interval_notifier_remove(struct mmu_interval_notifier *interval_sub)
+{
+	struct mm_struct *mm = interval_sub->mm;
+	struct mmu_notifier_subscriptions *subscriptions =
+		mm->notifier_subscriptions;
+	unsigned long seq = 0;
+
+	might_sleep();
+
+	spin_lock(&subscriptions->lock);
+	if (mn_itree_is_invalidating(subscriptions)) {
+		/*
+		 * remove is being called after insert put this on the
+		 * deferred list, but before the deferred list was processed.
+		 */
+		if (RB_EMPTY_NODE(&interval_sub->interval_tree.rb)) {
+			hlist_del(&interval_sub->deferred_item);
+		} else {
+			hlist_add_head(&interval_sub->deferred_item,
+				       &subscriptions->deferred_list);
+			seq = subscriptions->invalidate_seq;
+		}
+	} else {
+		WARN_ON(RB_EMPTY_NODE(&interval_sub->interval_tree.rb));
+		interval_tree_remove(&interval_sub->interval_tree,
+				     &subscriptions->itree);
+	}
+	spin_unlock(&subscriptions->lock);
+
+	/*
+	 * The possible sleep on progress in the invalidation requires the
+	 * caller not hold any locks held by invalidation callbacks.
+	 */
+	lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
+	lock_map_release(&__mmu_notifier_invalidate_range_start_map);
+	if (seq)
+		wait_event(subscriptions->wq,
+			   mmu_interval_seq_released(subscriptions, seq));
+
+	/* pairs with mmgrab in mmu_interval_notifier_insert() */
+	mmdrop(mm);
+}
+EXPORT_SYMBOL_GPL(mmu_interval_notifier_remove);
+
+/**
+ * mmu_notifier_synchronize - Ensure all mmu_notifiers are freed
+ *
+ * This function ensures that all outstanding async SRU work from
+ * mmu_notifier_put() is completed. After it returns any mmu_notifier_ops
+ * associated with an unused mmu_notifier will no longer be called.
+ *
+ * Before using the caller must ensure that all of its mmu_notifiers have been
+ * fully released via mmu_notifier_put().
+ *
+ * Modules using the mmu_notifier_put() API should call this in their __exit
+ * function to avoid module unloading races.
+ */
+void mmu_notifier_synchronize(void)
+{
+	synchronize_srcu(&srcu);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
+
+bool
+mmu_notifier_range_update_to_read_only(const struct mmu_notifier_range *range)
+{
+	if (!range->vma || range->event != MMU_NOTIFY_PROTECTION_VMA)
+		return false;
+	/* Return true if the vma still have the read flag set. */
+	return range->vma->vm_flags & VM_READ;
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_range_update_to_read_only);