17 files changed, 354 insertions, 383 deletions

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
index f2e8b4238efd..abc233088201 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
@@ -35,6 +35,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/vga_switcheroo.h>
 #include <drm/drm_probe_helper.h>
+#include <linux/mmu_notifier.h>
 
 #include "amdgpu.h"
 #include "amdgpu_irq.h"
@@ -1464,6 +1465,7 @@ static void __exit amdgpu_exit(void)
 	amdgpu_unregister_atpx_handler();
 	amdgpu_sync_fini();
 	amdgpu_fence_slab_fini();
+	mmu_notifier_synchronize();
 }
 
 module_init(amdgpu_init);
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
index 3933fb6a371e..9450e20d1709 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
@@ -686,9 +686,6 @@ struct kfd_process {
 	/* We want to receive a notification when the mm_struct is destroyed */
 	struct mmu_notifier mmu_notifier;
 
-	/* Use for delayed freeing of kfd_process structure */
-	struct rcu_head	rcu;
-
 	unsigned int pasid;
 	unsigned int doorbell_index;
 
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
index 8f1076c0c88a..e5e326f2f267 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
@@ -62,8 +62,8 @@ static struct workqueue_struct *kfd_restore_wq;
 
 static struct kfd_process *find_process(const struct task_struct *thread);
 static void kfd_process_ref_release(struct kref *ref);
-static struct kfd_process *create_process(const struct task_struct *thread,
-					struct file *filep);
+static struct kfd_process *create_process(const struct task_struct *thread);
+static int kfd_process_init_cwsr_apu(struct kfd_process *p, struct file *filep);
 
 static void evict_process_worker(struct work_struct *work);
 static void restore_process_worker(struct work_struct *work);
@@ -289,7 +289,15 @@ struct kfd_process *kfd_create_process(struct file *filep)
 	if (process) {
 		pr_debug("Process already found\n");
 	} else {
-		process = create_process(thread, filep);
+		process = create_process(thread);
+		if (IS_ERR(process))
+			goto out;
+
+		ret = kfd_process_init_cwsr_apu(process, filep);
+		if (ret) {
+			process = ERR_PTR(ret);
+			goto out;
+		}
 
 		if (!procfs.kobj)
 			goto out;
@@ -478,11 +486,9 @@ static void kfd_process_ref_release(struct kref *ref)
 	queue_work(kfd_process_wq, &p->release_work);
 }
 
-static void kfd_process_destroy_delayed(struct rcu_head *rcu)
+static void kfd_process_free_notifier(struct mmu_notifier *mn)
 {
-	struct kfd_process *p = container_of(rcu, struct kfd_process, rcu);
-
-	kfd_unref_process(p);
+	kfd_unref_process(container_of(mn, struct kfd_process, mmu_notifier));
 }
 
 static void kfd_process_notifier_release(struct mmu_notifier *mn,
@@ -534,12 +540,12 @@ static void kfd_process_notifier_release(struct mmu_notifier *mn,
 
 	mutex_unlock(&p->mutex);
 
-	mmu_notifier_unregister_no_release(&p->mmu_notifier, mm);
-	mmu_notifier_call_srcu(&p->rcu, &kfd_process_destroy_delayed);
+	mmu_notifier_put(&p->mmu_notifier);
 }
 
 static const struct mmu_notifier_ops kfd_process_mmu_notifier_ops = {
 	.release = kfd_process_notifier_release,
+	.free_notifier = kfd_process_free_notifier,
 };
 
 static int kfd_process_init_cwsr_apu(struct kfd_process *p, struct file *filep)
@@ -609,81 +615,69 @@ static int kfd_process_device_init_cwsr_dgpu(struct kfd_process_device *pdd)
 	return 0;
 }
 
-static struct kfd_process *create_process(const struct task_struct *thread,
-					struct file *filep)
+/*
+ * On return the kfd_process is fully operational and will be freed when the
+ * mm is released
+ */
+static struct kfd_process *create_process(const struct task_struct *thread)
 {
 	struct kfd_process *process;
 	int err = -ENOMEM;
 
 	process = kzalloc(sizeof(*process), GFP_KERNEL);
-
 	if (!process)
 		goto err_alloc_process;
 
-	process->pasid = kfd_pasid_alloc();
-	if (process->pasid == 0)
-		goto err_alloc_pasid;
-
-	if (kfd_alloc_process_doorbells(process) < 0)
-		goto err_alloc_doorbells;
-
 	kref_init(&process->ref);
-
 	mutex_init(&process->mutex);
-
 	process->mm = thread->mm;
-
-	/* register notifier */
-	process->mmu_notifier.ops = &kfd_process_mmu_notifier_ops;
-	err = mmu_notifier_register(&process->mmu_notifier, process->mm);
-	if (err)
-		goto err_mmu_notifier;
-
-	hash_add_rcu(kfd_processes_table, &process->kfd_processes,
-			(uintptr_t)process->mm);
-
 	process->lead_thread = thread->group_leader;
-	get_task_struct(process->lead_thread);
-
 	INIT_LIST_HEAD(&process->per_device_data);
-
+	INIT_DELAYED_WORK(&process->eviction_work, evict_process_worker);
+	INIT_DELAYED_WORK(&process->restore_work, restore_process_worker);
+	process->last_restore_timestamp = get_jiffies_64();
 	kfd_event_init_process(process);
+	process->is_32bit_user_mode = in_compat_syscall();
+
+	process->pasid = kfd_pasid_alloc();
+	if (process->pasid == 0)
+		goto err_alloc_pasid;
+
+	if (kfd_alloc_process_doorbells(process) < 0)
+		goto err_alloc_doorbells;
 
 	err = pqm_init(&process->pqm, process);
 	if (err != 0)
 		goto err_process_pqm_init;
 
 	/* init process apertures*/
-	process->is_32bit_user_mode = in_compat_syscall();
 	err = kfd_init_apertures(process);
 	if (err != 0)
 		goto err_init_apertures;
 
-	INIT_DELAYED_WORK(&process->eviction_work, evict_process_worker);
-	INIT_DELAYED_WORK(&process->restore_work, restore_process_worker);
-	process->last_restore_timestamp = get_jiffies_64();
-
-	err = kfd_process_init_cwsr_apu(process, filep);
+	/* Must be last, have to use release destruction after this */
+	process->mmu_notifier.ops = &kfd_process_mmu_notifier_ops;
+	err = mmu_notifier_register(&process->mmu_notifier, process->mm);
 	if (err)
-		goto err_init_cwsr;
+		goto err_register_notifier;
+
+	get_task_struct(process->lead_thread);
+	hash_add_rcu(kfd_processes_table, &process->kfd_processes,
+			(uintptr_t)process->mm);
 
 	return process;
 
-err_init_cwsr:
+err_register_notifier:
 	kfd_process_free_outstanding_kfd_bos(process);
 	kfd_process_destroy_pdds(process);
 err_init_apertures:
 	pqm_uninit(&process->pqm);
 err_process_pqm_init:
-	hash_del_rcu(&process->kfd_processes);
-	synchronize_rcu();
-	mmu_notifier_unregister_no_release(&process->mmu_notifier, process->mm);
-err_mmu_notifier:
-	mutex_destroy(&process->mutex);
 	kfd_free_process_doorbells(process);
 err_alloc_doorbells:
 	kfd_pasid_free(process->pasid);
 err_alloc_pasid:
+	mutex_destroy(&process->mutex);
 	kfree(process);
 err_alloc_process:
 	return ERR_PTR(err);
diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
index 7c2fcaba42d6..a0e48a482452 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
@@ -28,6 +28,7 @@
 #include <linux/pci.h>
 #include <linux/pm_runtime.h>
 #include <linux/vga_switcheroo.h>
+#include <linux/mmu_notifier.h>
 
 #include <drm/drmP.h>
 #include <drm/drm_crtc_helper.h>
@@ -1292,6 +1293,8 @@ nouveau_drm_exit(void)
 #ifdef CONFIG_NOUVEAU_PLATFORM_DRIVER
 	platform_driver_unregister(&nouveau_platform_driver);
 #endif
+	if (IS_ENABLED(CONFIG_DRM_NOUVEAU_SVM))
+		mmu_notifier_synchronize();
 }
 
 module_init(nouveau_drm_init);
diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index 32808e50be12..918164f90b11 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -2451,9 +2451,6 @@ struct radeon_device {
 	/* tracking pinned memory */
 	u64 vram_pin_size;
 	u64 gart_pin_size;
-
-	struct mutex	mn_lock;
-	DECLARE_HASHTABLE(mn_hash, 7);
 };
 
 bool radeon_is_px(struct drm_device *dev);
diff --git a/drivers/gpu/drm/radeon/radeon_device.c b/drivers/gpu/drm/radeon/radeon_device.c
index dceb554e5674..788b1d8a80e6 100644
--- a/drivers/gpu/drm/radeon/radeon_device.c
+++ b/drivers/gpu/drm/radeon/radeon_device.c
@@ -1325,8 +1325,6 @@ int radeon_device_init(struct radeon_device *rdev,
 	init_rwsem(&rdev->pm.mclk_lock);
 	init_rwsem(&rdev->exclusive_lock);
 	init_waitqueue_head(&rdev->irq.vblank_queue);
-	mutex_init(&rdev->mn_lock);
-	hash_init(rdev->mn_hash);
 	r = radeon_gem_init(rdev);
 	if (r)
 		return r;
diff --git a/drivers/gpu/drm/radeon/radeon_drv.c b/drivers/gpu/drm/radeon/radeon_drv.c
index a6cbe11f79c6..b6535ac91fdb 100644
--- a/drivers/gpu/drm/radeon/radeon_drv.c
+++ b/drivers/gpu/drm/radeon/radeon_drv.c
@@ -35,6 +35,7 @@
 #include <linux/module.h>
 #include <linux/pm_runtime.h>
 #include <linux/vga_switcheroo.h>
+#include <linux/mmu_notifier.h>
 
 #include <drm/drm_crtc_helper.h>
 #include <drm/drm_drv.h>
@@ -624,6 +625,7 @@ static void __exit radeon_exit(void)
 {
 	pci_unregister_driver(pdriver);
 	radeon_unregister_atpx_handler();
+	mmu_notifier_synchronize();
 }
 
 module_init(radeon_init);
diff --git a/drivers/gpu/drm/radeon/radeon_mn.c b/drivers/gpu/drm/radeon/radeon_mn.c
index 8c3871ed23a9..fc8254273a80 100644
--- a/drivers/gpu/drm/radeon/radeon_mn.c
+++ b/drivers/gpu/drm/radeon/radeon_mn.c
@@ -37,17 +37,8 @@
 #include "radeon.h"
 
 struct radeon_mn {
-	/* constant after initialisation */
-	struct radeon_device	*rdev;
-	struct mm_struct	*mm;
 	struct mmu_notifier	mn;
 
-	/* only used on destruction */
-	struct work_struct	work;
-
-	/* protected by rdev->mn_lock */
-	struct hlist_node	node;
-
 	/* objects protected by lock */
 	struct mutex		lock;
 	struct rb_root_cached	objects;
@@ -59,55 +50,6 @@ struct radeon_mn_node {
 };
 
 /**
- * radeon_mn_destroy - destroy the rmn
- *
- * @work: previously sheduled work item
- *
- * Lazy destroys the notifier from a work item
- */
-static void radeon_mn_destroy(struct work_struct *work)
-{
-	struct radeon_mn *rmn = container_of(work, struct radeon_mn, work);
-	struct radeon_device *rdev = rmn->rdev;
-	struct radeon_mn_node *node, *next_node;
-	struct radeon_bo *bo, *next_bo;
-
-	mutex_lock(&rdev->mn_lock);
-	mutex_lock(&rmn->lock);
-	hash_del(&rmn->node);
-	rbtree_postorder_for_each_entry_safe(node, next_node,
-					     &rmn->objects.rb_root, it.rb) {
-
-		interval_tree_remove(&node->it, &rmn->objects);
-		list_for_each_entry_safe(bo, next_bo, &node->bos, mn_list) {
-			bo->mn = NULL;
-			list_del_init(&bo->mn_list);
-		}
-		kfree(node);
-	}
-	mutex_unlock(&rmn->lock);
-	mutex_unlock(&rdev->mn_lock);
-	mmu_notifier_unregister(&rmn->mn, rmn->mm);
-	kfree(rmn);
-}
-
-/**
- * radeon_mn_release - callback to notify about mm destruction
- *
- * @mn: our notifier
- * @mn: the mm this callback is about
- *
- * Shedule a work item to lazy destroy our notifier.
- */
-static void radeon_mn_release(struct mmu_notifier *mn,
-			      struct mm_struct *mm)
-{
-	struct radeon_mn *rmn = container_of(mn, struct radeon_mn, mn);
-	INIT_WORK(&rmn->work, radeon_mn_destroy);
-	schedule_work(&rmn->work);
-}
-
-/**
  * radeon_mn_invalidate_range_start - callback to notify about mm change
  *
  * @mn: our notifier
@@ -183,65 +125,44 @@ out_unlock:
 	return ret;
 }
 
-static const struct mmu_notifier_ops radeon_mn_ops = {
-	.release = radeon_mn_release,
-	.invalidate_range_start = radeon_mn_invalidate_range_start,
-};
+static void radeon_mn_release(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	struct mmu_notifier_range range = {
+		.mm = mm,
+		.start = 0,
+		.end = ULONG_MAX,
+		.flags = 0,
+		.event = MMU_NOTIFY_UNMAP,
+	};
+
+	radeon_mn_invalidate_range_start(mn, &range);
+}
 
-/**
- * radeon_mn_get - create notifier context
- *
- * @rdev: radeon device pointer
- *
- * Creates a notifier context for current->mm.
- */
-static struct radeon_mn *radeon_mn_get(struct radeon_device *rdev)
+static struct mmu_notifier *radeon_mn_alloc_notifier(struct mm_struct *mm)
 {
-	struct mm_struct *mm = current->mm;
 	struct radeon_mn *rmn;
-	int r;
-
-	if (down_write_killable(&mm->mmap_sem))
-		return ERR_PTR(-EINTR);
-
-	mutex_lock(&rdev->mn_lock);
-
-	hash_for_each_possible(rdev->mn_hash, rmn, node, (unsigned long)mm)
-		if (rmn->mm == mm)
-			goto release_locks;
 
 	rmn = kzalloc(sizeof(*rmn), GFP_KERNEL);
-	if (!rmn) {
-		rmn = ERR_PTR(-ENOMEM);
-		goto release_locks;
-	}
+	if (!rmn)
+		return ERR_PTR(-ENOMEM);
 
-	rmn->rdev = rdev;
-	rmn->mm = mm;
-	rmn->mn.ops = &radeon_mn_ops;
 	mutex_init(&rmn->lock);
 	rmn->objects = RB_ROOT_CACHED;
-	
-	r = __mmu_notifier_register(&rmn->mn, mm);
-	if (r)
-		goto free_rmn;
-
-	hash_add(rdev->mn_hash, &rmn->node, (unsigned long)mm);
-
-release_locks:
-	mutex_unlock(&rdev->mn_lock);
-	up_write(&mm->mmap_sem);
-
-	return rmn;
-
-free_rmn:
-	mutex_unlock(&rdev->mn_lock);
-	up_write(&mm->mmap_sem);
-	kfree(rmn);
+	return &rmn->mn;
+}
 
-	return ERR_PTR(r);
+static void radeon_mn_free_notifier(struct mmu_notifier *mn)
+{
+	kfree(container_of(mn, struct radeon_mn, mn));
 }
 
+static const struct mmu_notifier_ops radeon_mn_ops = {
+	.release = radeon_mn_release,
+	.invalidate_range_start = radeon_mn_invalidate_range_start,
+	.alloc_notifier = radeon_mn_alloc_notifier,
+	.free_notifier = radeon_mn_free_notifier,
+};
+
 /**
  * radeon_mn_register - register a BO for notifier updates
  *
@@ -254,15 +175,16 @@ free_rmn:
 int radeon_mn_register(struct radeon_bo *bo, unsigned long addr)
 {
 	unsigned long end = addr + radeon_bo_size(bo) - 1;
-	struct radeon_device *rdev = bo->rdev;
+	struct mmu_notifier *mn;
 	struct radeon_mn *rmn;
 	struct radeon_mn_node *node = NULL;
 	struct list_head bos;
 	struct interval_tree_node *it;
 
-	rmn = radeon_mn_get(rdev);
-	if (IS_ERR(rmn))
-		return PTR_ERR(rmn);
+	mn = mmu_notifier_get(&radeon_mn_ops, current->mm);
+	if (IS_ERR(mn))
+		return PTR_ERR(mn);
+	rmn = container_of(mn, struct radeon_mn, mn);
 
 	INIT_LIST_HEAD(&bos);
 
@@ -309,22 +231,13 @@ int radeon_mn_register(struct radeon_bo *bo, unsigned long addr)
  */
 void radeon_mn_unregister(struct radeon_bo *bo)
 {
-	struct radeon_device *rdev = bo->rdev;
-	struct radeon_mn *rmn;
+	struct radeon_mn *rmn = bo->mn;
 	struct list_head *head;
 
-	mutex_lock(&rdev->mn_lock);
-	rmn = bo->mn;
-	if (rmn == NULL) {
-		mutex_unlock(&rdev->mn_lock);
-		return;
-	}
-
 	mutex_lock(&rmn->lock);
 	/* save the next list entry for later */
 	head = bo->mn_list.next;
 
-	bo->mn = NULL;
 	list_del(&bo->mn_list);
 
 	if (list_empty(head)) {
@@ -335,5 +248,7 @@ void radeon_mn_unregister(struct radeon_bo *bo)
 	}
 
 	mutex_unlock(&rmn->lock);
-	mutex_unlock(&rdev->mn_lock);
+
+	mmu_notifier_put(&rmn->mn);
+	bo->mn = NULL;
 }
diff --git a/drivers/misc/sgi-gru/grufile.c b/drivers/misc/sgi-gru/grufile.c
index a2a142ae087b..9d042310214f 100644
--- a/drivers/misc/sgi-gru/grufile.c
+++ b/drivers/misc/sgi-gru/grufile.c
@@ -573,6 +573,7 @@ static void __exit gru_exit(void)
 	gru_free_tables();
 	misc_deregister(&gru_miscdev);
 	gru_proc_exit();
+	mmu_notifier_synchronize();
 }
 
 static const struct file_operations gru_fops = {
diff --git a/drivers/misc/sgi-gru/grutables.h b/drivers/misc/sgi-gru/grutables.h
index 438191c22057..a7e44b2eb413 100644
--- a/drivers/misc/sgi-gru/grutables.h
+++ b/drivers/misc/sgi-gru/grutables.h
@@ -307,10 +307,8 @@ struct gru_mm_tracker {				/* pack to reduce size */
 
 struct gru_mm_struct {
 	struct mmu_notifier	ms_notifier;
-	atomic_t		ms_refcnt;
 	spinlock_t		ms_asid_lock;	/* protects ASID assignment */
 	atomic_t		ms_range_active;/* num range_invals active */
-	char			ms_released;
 	wait_queue_head_t	ms_wait_queue;
 	DECLARE_BITMAP(ms_asidmap, GRU_MAX_GRUS);
 	struct gru_mm_tracker	ms_asids[GRU_MAX_GRUS];
diff --git a/drivers/misc/sgi-gru/grutlbpurge.c b/drivers/misc/sgi-gru/grutlbpurge.c
index 59ba0adf23ce..10921cd2608d 100644
--- a/drivers/misc/sgi-gru/grutlbpurge.c
+++ b/drivers/misc/sgi-gru/grutlbpurge.c
@@ -235,83 +235,47 @@ static void gru_invalidate_range_end(struct mmu_notifier *mn,
 		gms, range->start, range->end);
 }
 
-static void gru_release(struct mmu_notifier *mn, struct mm_struct *mm)
+static struct mmu_notifier *gru_alloc_notifier(struct mm_struct *mm)
 {
-	struct gru_mm_struct *gms = container_of(mn, struct gru_mm_struct,
-						 ms_notifier);
+	struct gru_mm_struct *gms;
+
+	gms = kzalloc(sizeof(*gms), GFP_KERNEL);
+	if (!gms)
+		return ERR_PTR(-ENOMEM);
+	STAT(gms_alloc);
+	spin_lock_init(&gms->ms_asid_lock);
+	init_waitqueue_head(&gms->ms_wait_queue);
 
-	gms->ms_released = 1;
-	gru_dbg(grudev, "gms %p\n", gms);
+	return &gms->ms_notifier;
 }
 
+static void gru_free_notifier(struct mmu_notifier *mn)
+{
+	kfree(container_of(mn, struct gru_mm_struct, ms_notifier));
+	STAT(gms_free);
+}
 
 static const struct mmu_notifier_ops gru_mmuops = {
 	.invalidate_range_start	= gru_invalidate_range_start,
 	.invalidate_range_end	= gru_invalidate_range_end,
-	.release		= gru_release,
+	.alloc_notifier		= gru_alloc_notifier,
+	.free_notifier		= gru_free_notifier,
 };
 
-/* Move this to the basic mmu_notifier file. But for now... */
-static struct mmu_notifier *mmu_find_ops(struct mm_struct *mm,
-			const struct mmu_notifier_ops *ops)
-{
-	struct mmu_notifier *mn, *gru_mn = NULL;
-
-	if (mm->mmu_notifier_mm) {
-		rcu_read_lock();
-		hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list,
-					 hlist)
-		    if (mn->ops == ops) {
-			gru_mn = mn;
-			break;
-		}
-		rcu_read_unlock();
-	}
-	return gru_mn;
-}
-
 struct gru_mm_struct *gru_register_mmu_notifier(void)
 {
-	struct gru_mm_struct *gms;
 	struct mmu_notifier *mn;
-	int err;
-
-	mn = mmu_find_ops(current->mm, &gru_mmuops);
-	if (mn) {
-		gms = container_of(mn, struct gru_mm_struct, ms_notifier);
-		atomic_inc(&gms->ms_refcnt);
-	} else {
-		gms = kzalloc(sizeof(*gms), GFP_KERNEL);
-		if (!gms)
-			return ERR_PTR(-ENOMEM);
-		STAT(gms_alloc);
-		spin_lock_init(&gms->ms_asid_lock);
-		gms->ms_notifier.ops = &gru_mmuops;
-		atomic_set(&gms->ms_refcnt, 1);
-		init_waitqueue_head(&gms->ms_wait_queue);
-		err = __mmu_notifier_register(&gms->ms_notifier, current->mm);
-		if (err)
-			goto error;
-	}
-	if (gms)
-		gru_dbg(grudev, "gms %p, refcnt %d\n", gms,
-			atomic_read(&gms->ms_refcnt));
-	return gms;
-error:
-	kfree(gms);
-	return ERR_PTR(err);
+
+	mn = mmu_notifier_get_locked(&gru_mmuops, current->mm);
+	if (IS_ERR(mn))
+		return ERR_CAST(mn);
+
+	return container_of(mn, struct gru_mm_struct, ms_notifier);
 }
 
 void gru_drop_mmu_notifier(struct gru_mm_struct *gms)
 {
-	gru_dbg(grudev, "gms %p, refcnt %d, released %d\n", gms,
-		atomic_read(&gms->ms_refcnt), gms->ms_released);
-	if (atomic_dec_return(&gms->ms_refcnt) == 0) {
-		if (!gms->ms_released)
-			mmu_notifier_unregister(&gms->ms_notifier, current->mm);
-		kfree(gms);
-		STAT(gms_free);
-	}
+	mmu_notifier_put(&gms->ms_notifier);
 }
 
 /*
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 51e18fbb8953..3fec513b9c00 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -84,15 +84,12 @@
  * @notifiers: count of active mmu notifiers
  */
 struct hmm {
-	struct mm_struct	*mm;
-	struct kref		kref;
+	struct mmu_notifier	mmu_notifier;
 	spinlock_t		ranges_lock;
 	struct list_head	ranges;
 	struct list_head	mirrors;
-	struct mmu_notifier	mmu_notifier;
 	struct rw_semaphore	mirrors_sem;
 	wait_queue_head_t	wq;
-	struct rcu_head		rcu;
 	long			notifiers;
 };
 
@@ -409,13 +406,6 @@ long hmm_range_dma_unmap(struct hmm_range *range,
  */
 #define HMM_RANGE_DEFAULT_TIMEOUT 1000
 
-/* Below are for HMM internal use only! Not to be used by device driver! */
-static inline void hmm_mm_init(struct mm_struct *mm)
-{
-	mm->hmm = NULL;
-}
-#else /* IS_ENABLED(CONFIG_HMM_MIRROR) */
-static inline void hmm_mm_init(struct mm_struct *mm) {}
 #endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
 
 #endif /* LINUX_HMM_H */
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 3a37a89eb7a7..525d25d93330 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -25,7 +25,6 @@
 
 struct address_space;
 struct mem_cgroup;
-struct hmm;
 
 /*
  * Each physical page in the system has a struct page associated with
@@ -502,11 +501,6 @@ struct mm_struct {
 		atomic_long_t hugetlb_usage;
 #endif
 		struct work_struct async_put_work;
-
-#ifdef CONFIG_HMM_MIRROR
-		/* HMM needs to track a few things per mm */
-		struct hmm *hmm;
-#endif
 	} __randomize_layout;
 
 	/*
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index b6c004bd9f6a..31aa971315a1 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -211,6 +211,19 @@ struct mmu_notifier_ops {
 	 */
 	void (*invalidate_range)(struct mmu_notifier *mn, struct mm_struct *mm,
 				 unsigned long start, unsigned long end);
+
+	/*
+	 * These callbacks are used with the get/put interface to manage the
+	 * lifetime of the mmu_notifier memory. alloc_notifier() returns a new
+	 * notifier for use with the mm.
+	 *
+	 * free_notifier() is only called after the mmu_notifier has been
+	 * fully put, calls to any ops callback are prevented and no ops
+	 * callbacks are currently running. It is called from a SRCU callback
+	 * and cannot sleep.
+	 */
+	struct mmu_notifier *(*alloc_notifier)(struct mm_struct *mm);
+	void (*free_notifier)(struct mmu_notifier *mn);
 };
 
 /*
@@ -227,6 +240,9 @@ struct mmu_notifier_ops {
 struct mmu_notifier {
 	struct hlist_node hlist;
 	const struct mmu_notifier_ops *ops;
+	struct mm_struct *mm;
+	struct rcu_head rcu;
+	unsigned int users;
 };
 
 static inline int mm_has_notifiers(struct mm_struct *mm)
@@ -234,6 +250,21 @@ static inline int mm_has_notifiers(struct mm_struct *mm)
 	return unlikely(mm->mmu_notifier_mm);
 }
 
+struct mmu_notifier *mmu_notifier_get_locked(const struct mmu_notifier_ops *ops,
+					     struct mm_struct *mm);
+static inline struct mmu_notifier *
+mmu_notifier_get(const struct mmu_notifier_ops *ops, struct mm_struct *mm)
+{
+	struct mmu_notifier *ret;
+
+	down_write(&mm->mmap_sem);
+	ret = mmu_notifier_get_locked(ops, mm);
+	up_write(&mm->mmap_sem);
+	return ret;
+}
+void mmu_notifier_put(struct mmu_notifier *mn);
+void mmu_notifier_synchronize(void);
+
 extern int mmu_notifier_register(struct mmu_notifier *mn,
 				 struct mm_struct *mm);
 extern int __mmu_notifier_register(struct mmu_notifier *mn,
@@ -581,6 +612,10 @@ static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
 #define pudp_huge_clear_flush_notify pudp_huge_clear_flush
 #define set_pte_at_notify set_pte_at
 
+static inline void mmu_notifier_synchronize(void)
+{
+}
+
 #endif /* CONFIG_MMU_NOTIFIER */
 
 #endif /* _LINUX_MMU_NOTIFIER_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index d8ae0f1b4148..bd4a0762f12f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1007,7 +1007,6 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 	mm_init_owner(mm, p);
 	RCU_INIT_POINTER(mm->exe_file, NULL);
 	mmu_notifier_mm_init(mm);
-	hmm_mm_init(mm);
 	init_tlb_flush_pending(mm);
 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 	mm->pmd_huge_pte = NULL;
diff --git a/mm/hmm.c b/mm/hmm.c
index ef553e664061..49eace16f9f8 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -26,101 +26,37 @@
 #include <linux/mmu_notifier.h>
 #include <linux/memory_hotplug.h>
 
-static const struct mmu_notifier_ops hmm_mmu_notifier_ops;
-
-/**
- * hmm_get_or_create - register HMM against an mm (HMM internal)
- *
- * @mm: mm struct to attach to
- * Return: an HMM object, either by referencing the existing
- *          (per-process) object, or by creating a new one.
- *
- * This is not intended to be used directly by device drivers. If mm already
- * has an HMM struct then it get a reference on it and returns it. Otherwise
- * it allocates an HMM struct, initializes it, associate it with the mm and
- * returns it.
- */
-static struct hmm *hmm_get_or_create(struct mm_struct *mm)
+static struct mmu_notifier *hmm_alloc_notifier(struct mm_struct *mm)
 {
 	struct hmm *hmm;
 
-	lockdep_assert_held_write(&mm->mmap_sem);
-
-	/* Abuse the page_table_lock to also protect mm->hmm. */
-	spin_lock(&mm->page_table_lock);
-	hmm = mm->hmm;
-	if (mm->hmm && kref_get_unless_zero(&mm->hmm->kref))
-		goto out_unlock;
-	spin_unlock(&mm->page_table_lock);
-
-	hmm = kmalloc(sizeof(*hmm), GFP_KERNEL);
+	hmm = kzalloc(sizeof(*hmm), GFP_KERNEL);
 	if (!hmm)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
+
 	init_waitqueue_head(&hmm->wq);
 	INIT_LIST_HEAD(&hmm->mirrors);
 	init_rwsem(&hmm->mirrors_sem);
-	hmm->mmu_notifier.ops = NULL;
 	INIT_LIST_HEAD(&hmm->ranges);
 	spin_lock_init(&hmm->ranges_lock);
-	kref_init(&hmm->kref);
 	hmm->notifiers = 0;
-	hmm->mm = mm;
-
-	hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops;
-	if (__mmu_notifier_register(&hmm->mmu_notifier, mm)) {
-		kfree(hmm);
-		return NULL;
-	}
-
-	mmgrab(hmm->mm);
-
-	/*
-	 * We hold the exclusive mmap_sem here so we know that mm->hmm is
-	 * still NULL or 0 kref, and is safe to update.
-	 */
-	spin_lock(&mm->page_table_lock);
-	mm->hmm = hmm;
-
-out_unlock:
-	spin_unlock(&mm->page_table_lock);
-	return hmm;
+	return &hmm->mmu_notifier;
 }
 
-static void hmm_free_rcu(struct rcu_head *rcu)
+static void hmm_free_notifier(struct mmu_notifier *mn)
 {
-	struct hmm *hmm = container_of(rcu, struct hmm, rcu);
+	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);
 
-	mmdrop(hmm->mm);
+	WARN_ON(!list_empty(&hmm->ranges));
+	WARN_ON(!list_empty(&hmm->mirrors));
 	kfree(hmm);
 }
 
-static void hmm_free(struct kref *kref)
-{
-	struct hmm *hmm = container_of(kref, struct hmm, kref);
-
-	spin_lock(&hmm->mm->page_table_lock);
-	if (hmm->mm->hmm == hmm)
-		hmm->mm->hmm = NULL;
-	spin_unlock(&hmm->mm->page_table_lock);
-
-	mmu_notifier_unregister_no_release(&hmm->mmu_notifier, hmm->mm);
-	mmu_notifier_call_srcu(&hmm->rcu, hmm_free_rcu);
-}
-
-static inline void hmm_put(struct hmm *hmm)
-{
-	kref_put(&hmm->kref, hmm_free);
-}
-
 static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
 {
 	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);
 	struct hmm_mirror *mirror;
 
-	/* Bail out if hmm is in the process of being freed */
-	if (!kref_get_unless_zero(&hmm->kref))
-		return;
-
 	/*
 	 * Since hmm_range_register() holds the mmget() lock hmm_release() is
 	 * prevented as long as a range exists.
@@ -137,8 +73,6 @@ static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
 			mirror->ops->release(mirror);
 	}
 	up_read(&hmm->mirrors_sem);
-
-	hmm_put(hmm);
 }
 
 static void notifiers_decrement(struct hmm *hmm)
@@ -169,9 +103,6 @@ static int hmm_invalidate_range_start(struct mmu_notifier *mn,
 	unsigned long flags;
 	int ret = 0;
 
-	if (!kref_get_unless_zero(&hmm->kref))
-		return 0;
-
 	spin_lock_irqsave(&hmm->ranges_lock, flags);
 	hmm->notifiers++;
 	list_for_each_entry(range, &hmm->ranges, list) {
@@ -206,7 +137,6 @@ static int hmm_invalidate_range_start(struct mmu_notifier *mn,
 out:
 	if (ret)
 		notifiers_decrement(hmm);
-	hmm_put(hmm);
 	return ret;
 }
 
@@ -215,17 +145,15 @@ static void hmm_invalidate_range_end(struct mmu_notifier *mn,
 {
 	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);
 
-	if (!kref_get_unless_zero(&hmm->kref))
-		return;
-
 	notifiers_decrement(hmm);
-	hmm_put(hmm);
 }
 
 static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {
 	.release		= hmm_release,
 	.invalidate_range_start	= hmm_invalidate_range_start,
 	.invalidate_range_end	= hmm_invalidate_range_end,
+	.alloc_notifier		= hmm_alloc_notifier,
+	.free_notifier		= hmm_free_notifier,
 };
 
 /*
@@ -237,18 +165,27 @@ static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {
  *
  * To start mirroring a process address space, the device driver must register
  * an HMM mirror struct.
+ *
+ * The caller cannot unregister the hmm_mirror while any ranges are
+ * registered.
+ *
+ * Callers using this function must put a call to mmu_notifier_synchronize()
+ * in their module exit functions.
  */
 int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
 {
+	struct mmu_notifier *mn;
+
 	lockdep_assert_held_write(&mm->mmap_sem);
 
 	/* Sanity check */
 	if (!mm || !mirror || !mirror->ops)
 		return -EINVAL;
 
-	mirror->hmm = hmm_get_or_create(mm);
-	if (!mirror->hmm)
-		return -ENOMEM;
+	mn = mmu_notifier_get_locked(&hmm_mmu_notifier_ops, mm);
+	if (IS_ERR(mn))
+		return PTR_ERR(mn);
+	mirror->hmm = container_of(mn, struct hmm, mmu_notifier);
 
 	down_write(&mirror->hmm->mirrors_sem);
 	list_add(&mirror->list, &mirror->hmm->mirrors);
@@ -272,7 +209,7 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror)
 	down_write(&hmm->mirrors_sem);
 	list_del(&mirror->list);
 	up_write(&hmm->mirrors_sem);
-	hmm_put(hmm);
+	mmu_notifier_put(&hmm->mmu_notifier);
 }
 EXPORT_SYMBOL(hmm_mirror_unregister);
 
@@ -854,14 +791,13 @@ int hmm_range_register(struct hmm_range *range, struct hmm_mirror *mirror)
 		return -EINVAL;
 
 	/* Prevent hmm_release() from running while the range is valid */
-	if (!mmget_not_zero(hmm->mm))
+	if (!mmget_not_zero(hmm->mmu_notifier.mm))
 		return -EFAULT;
 
 	/* Initialize range to track CPU page table updates. */
 	spin_lock_irqsave(&hmm->ranges_lock, flags);
 
 	range->hmm = hmm;
-	kref_get(&hmm->kref);
 	list_add(&range->list, &hmm->ranges);
 
 	/*
@@ -893,8 +829,7 @@ void hmm_range_unregister(struct hmm_range *range)
 	spin_unlock_irqrestore(&hmm->ranges_lock, flags);
 
 	/* Drop reference taken by hmm_range_register() */
-	mmput(hmm->mm);
-	hmm_put(hmm);
+	mmput(hmm->mmu_notifier.mm);
 
 	/*
 	 * The range is now invalid and the ref on the hmm is dropped, so
@@ -944,14 +879,14 @@ long hmm_range_fault(struct hmm_range *range, unsigned int flags)
 	struct mm_walk mm_walk;
 	int ret;
 
-	lockdep_assert_held(&hmm->mm->mmap_sem);
+	lockdep_assert_held(&hmm->mmu_notifier.mm->mmap_sem);
 
 	do {
 		/* If range is no longer valid force retry. */
 		if (!range->valid)
 			return -EBUSY;
 
-		vma = find_vma(hmm->mm, start);
+		vma = find_vma(hmm->mmu_notifier.mm, start);
 		if (vma == NULL || (vma->vm_flags & device_vma))
 			return -EFAULT;
 
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index b5670620aea0..9e92ec8006fc 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -236,33 +236,41 @@ void __mmu_notifier_invalidate_range(struct mm_struct *mm,
 }
 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)
+/*
+ * 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)
 {
-	struct mmu_notifier_mm *mmu_notifier_mm;
+	struct mmu_notifier_mm *mmu_notifier_mm = NULL;
 	int ret;
 
+	lockdep_assert_held_write(&mm->mmap_sem);
 	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;
+	mn->mm = mm;
+	mn->users = 1;
 
-	if (take_mmap_sem)
-		down_write(&mm->mmap_sem);
-	ret = mm_take_all_locks(mm);
-	if (unlikely(ret))
-		goto out_clean;
+	if (!mm->mmu_notifier_mm) {
+		/*
+		 * kmalloc cannot be called under mm_take_all_locks(), but we
+		 * know that mm->mmu_notifier_mm can't change while we hold
+		 * the write side of the mmap_sem.
+		 */
+		mmu_notifier_mm =
+			kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
+		if (!mmu_notifier_mm)
+			return -ENOMEM;
 
-	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;
 	}
+
+	ret = mm_take_all_locks(mm);
+	if (unlikely(ret))
+		goto out_clean;
+
+	/* Pairs with the mmdrop in mmu_notifier_unregister_* */
 	mmgrab(mm);
 
 	/*
@@ -273,48 +281,118 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
 	 * We can't race against any other mmu notifier method either
 	 * thanks to mm_take_all_locks().
 	 */
+	if (mmu_notifier_mm)
+		mm->mmu_notifier_mm = mmu_notifier_mm;
+
 	spin_lock(&mm->mmu_notifier_mm->lock);
 	hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier_mm->list);
 	spin_unlock(&mm->mmu_notifier_mm->lock);
 
 	mm_drop_all_locks(mm);
+	BUG_ON(atomic_read(&mm->mm_users) <= 0);
+	return 0;
+
 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;
 }
+EXPORT_SYMBOL_GPL(__mmu_notifier_register);
 
-/*
+/**
+ * mmu_notifier_register - Register a notifier on a mm
+ * @mn: The notifier to attach
+ * @mm: The mm to attach the notifier to
+ *
  * 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.
+ * 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 mn->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 *mn, struct mm_struct *mm)
 {
-	return do_mmu_notifier_register(mn, mm, 1);
+	int ret;
+
+	down_write(&mm->mmap_sem);
+	ret = __mmu_notifier_register(mn, mm);
+	up_write(&mm->mmap_sem);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(mmu_notifier_register);
 
-/*
- * Same as mmu_notifier_register but here the caller must hold the
- * mmap_sem in write mode.
+static struct mmu_notifier *
+find_get_mmu_notifier(struct mm_struct *mm, const struct mmu_notifier_ops *ops)
+{
+	struct mmu_notifier *mn;
+
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	hlist_for_each_entry_rcu (mn, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops != ops)
+			continue;
+
+		if (likely(mn->users != UINT_MAX))
+			mn->users++;
+		else
+			mn = ERR_PTR(-EOVERFLOW);
+		spin_unlock(&mm->mmu_notifier_mm->lock);
+		return mn;
+	}
+	spin_unlock(&mm->mmu_notifier_mm->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_sem.
+ *
+ * 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().
  */
-int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
+struct mmu_notifier *mmu_notifier_get_locked(const struct mmu_notifier_ops *ops,
+					     struct mm_struct *mm)
 {
-	return do_mmu_notifier_register(mn, mm, 0);
+	struct mmu_notifier *mn;
+	int ret;
+
+	lockdep_assert_held_write(&mm->mmap_sem);
+
+	if (mm->mmu_notifier_mm) {
+		mn = find_get_mmu_notifier(mm, ops);
+		if (mn)
+			return mn;
+	}
+
+	mn = ops->alloc_notifier(mm);
+	if (IS_ERR(mn))
+		return mn;
+	mn->ops = ops;
+	ret = __mmu_notifier_register(mn, mm);
+	if (ret)
+		goto out_free;
+	return mn;
+out_free:
+	mn->ops->free_notifier(mn);
+	return ERR_PTR(ret);
 }
-EXPORT_SYMBOL_GPL(__mmu_notifier_register);
+EXPORT_SYMBOL_GPL(mmu_notifier_get_locked);
 
 /* this is called after the last mmu_notifier_unregister() returned */
 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
@@ -394,6 +472,75 @@ void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
 }
 EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
 
+static void mmu_notifier_free_rcu(struct rcu_head *rcu)
+{
+	struct mmu_notifier *mn = container_of(rcu, struct mmu_notifier, rcu);
+	struct mm_struct *mm = mn->mm;
+
+	mn->ops->free_notifier(mn);
+	/* Pairs with the get in __mmu_notifier_register() */
+	mmdrop(mm);
+}
+
+/**
+ * mmu_notifier_put - Release the reference on the notifier
+ * @mn: 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 *mn)
+{
+	struct mm_struct *mm = mn->mm;
+
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	if (WARN_ON(!mn->users) || --mn->users)
+		goto out_unlock;
+	hlist_del_init_rcu(&mn->hlist);
+	spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	call_srcu(&srcu, &mn->rcu, mmu_notifier_free_rcu);
+	return;
+
+out_unlock:
+	spin_unlock(&mm->mmu_notifier_mm->lock);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_put);
+
+/**
+ * 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)
 {