Revert "vhost: access vq metadata through kernel virtual address"

This reverts commit 7f466032 ("vhost: access vq metadata through
kernel virtual address").  The commit caused a bunch of issues, and
while commit 73f628ec ("vhost: disable metadata prefetch
optimization") disabled the optimization it's not nice to keep lots of
dead code around.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vhost.c

@@ -297,160 +297,6 @@ static void vhost_vq_meta_reset(struct vhost_dev *d)
 		__vhost_vq_meta_reset(d->vqs[i]);
 }
 
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-static void vhost_map_unprefetch(struct vhost_map *map)
-{
-	kfree(map->pages);
-	map->pages = NULL;
-	map->npages = 0;
-	map->addr = NULL;
-}
-
-static void vhost_uninit_vq_maps(struct vhost_virtqueue *vq)
-{
-	struct vhost_map *map[VHOST_NUM_ADDRS];
-	int i;
-
-	spin_lock(&vq->mmu_lock);
-	for (i = 0; i < VHOST_NUM_ADDRS; i++) {
-		map[i] = rcu_dereference_protected(vq->maps[i],
-				  lockdep_is_held(&vq->mmu_lock));
-		if (map[i])
-			rcu_assign_pointer(vq->maps[i], NULL);
-	}
-	spin_unlock(&vq->mmu_lock);
-
-	synchronize_rcu();
-
-	for (i = 0; i < VHOST_NUM_ADDRS; i++)
-		if (map[i])
-			vhost_map_unprefetch(map[i]);
-
-}
-
-static void vhost_reset_vq_maps(struct vhost_virtqueue *vq)
-{
-	int i;
-
-	vhost_uninit_vq_maps(vq);
-	for (i = 0; i < VHOST_NUM_ADDRS; i++)
-		vq->uaddrs[i].size = 0;
-}
-
-static bool vhost_map_range_overlap(struct vhost_uaddr *uaddr,
-				     unsigned long start,
-				     unsigned long end)
-{
-	if (unlikely(!uaddr->size))
-		return false;
-
-	return !(end < uaddr->uaddr || start > uaddr->uaddr - 1 + uaddr->size);
-}
-
-static void vhost_invalidate_vq_start(struct vhost_virtqueue *vq,
-				      int index,
-				      unsigned long start,
-				      unsigned long end)
-{
-	struct vhost_uaddr *uaddr = &vq->uaddrs[index];
-	struct vhost_map *map;
-	int i;
-
-	if (!vhost_map_range_overlap(uaddr, start, end))
-		return;
-
-	spin_lock(&vq->mmu_lock);
-	++vq->invalidate_count;
-
-	map = rcu_dereference_protected(vq->maps[index],
-					lockdep_is_held(&vq->mmu_lock));
-	if (map) {
-		if (uaddr->write) {
-			for (i = 0; i < map->npages; i++)
-				set_page_dirty(map->pages[i]);
-		}
-		rcu_assign_pointer(vq->maps[index], NULL);
-	}
-	spin_unlock(&vq->mmu_lock);
-
-	if (map) {
-		synchronize_rcu();
-		vhost_map_unprefetch(map);
-	}
-}
-
-static void vhost_invalidate_vq_end(struct vhost_virtqueue *vq,
-				    int index,
-				    unsigned long start,
-				    unsigned long end)
-{
-	if (!vhost_map_range_overlap(&vq->uaddrs[index], start, end))
-		return;
-
-	spin_lock(&vq->mmu_lock);
-	--vq->invalidate_count;
-	spin_unlock(&vq->mmu_lock);
-}
-
-static int vhost_invalidate_range_start(struct mmu_notifier *mn,
-					const struct mmu_notifier_range *range)
-{
-	struct vhost_dev *dev = container_of(mn, struct vhost_dev,
-					     mmu_notifier);
-	int i, j;
-
-	if (!mmu_notifier_range_blockable(range))
-		return -EAGAIN;
-
-	for (i = 0; i < dev->nvqs; i++) {
-		struct vhost_virtqueue *vq = dev->vqs[i];
-
-		for (j = 0; j < VHOST_NUM_ADDRS; j++)
-			vhost_invalidate_vq_start(vq, j,
-						  range->start,
-						  range->end);
-	}
-
-	return 0;
-}
-
-static void vhost_invalidate_range_end(struct mmu_notifier *mn,
-				       const struct mmu_notifier_range *range)
-{
-	struct vhost_dev *dev = container_of(mn, struct vhost_dev,
-					     mmu_notifier);
-	int i, j;
-
-	for (i = 0; i < dev->nvqs; i++) {
-		struct vhost_virtqueue *vq = dev->vqs[i];
-
-		for (j = 0; j < VHOST_NUM_ADDRS; j++)
-			vhost_invalidate_vq_end(vq, j,
-						range->start,
-						range->end);
-	}
-}
-
-static const struct mmu_notifier_ops vhost_mmu_notifier_ops = {
-	.invalidate_range_start = vhost_invalidate_range_start,
-	.invalidate_range_end = vhost_invalidate_range_end,
-};
-
-static void vhost_init_maps(struct vhost_dev *dev)
-{
-	struct vhost_virtqueue *vq;
-	int i, j;
-
-	dev->mmu_notifier.ops = &vhost_mmu_notifier_ops;
-
-	for (i = 0; i < dev->nvqs; ++i) {
-		vq = dev->vqs[i];
-		for (j = 0; j < VHOST_NUM_ADDRS; j++)
-			RCU_INIT_POINTER(vq->maps[j], NULL);
-	}
-}
-#endif
-
 static void vhost_vq_reset(struct vhost_dev *dev,
 			   struct vhost_virtqueue *vq)
 {
@@ -479,11 +325,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 	vq->busyloop_timeout = 0;
 	vq->umem = NULL;
 	vq->iotlb = NULL;
-	vq->invalidate_count = 0;
 	__vhost_vq_meta_reset(vq);
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	vhost_reset_vq_maps(vq);
-#endif
 }
 
 static int vhost_worker(void *data)
@@ -633,9 +475,7 @@ void vhost_dev_init(struct vhost_dev *dev,
 	INIT_LIST_HEAD(&dev->read_list);
 	INIT_LIST_HEAD(&dev->pending_list);
 	spin_lock_init(&dev->iotlb_lock);
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	vhost_init_maps(dev);
-#endif
+
 
 	for (i = 0; i < dev->nvqs; ++i) {
 		vq = dev->vqs[i];
@@ -644,7 +484,6 @@ void vhost_dev_init(struct vhost_dev *dev,
 		vq->heads = NULL;
 		vq->dev = dev;
 		mutex_init(&vq->mutex);
-		spin_lock_init(&vq->mmu_lock);
 		vhost_vq_reset(dev, vq);
 		if (vq->handle_kick)
 			vhost_poll_init(&vq->poll, vq->handle_kick,
@@ -724,18 +563,7 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
 	if (err)
 		goto err_cgroup;
 
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	err = mmu_notifier_register(&dev->mmu_notifier, dev->mm);
-	if (err)
-		goto err_mmu_notifier;
-#endif
-
 	return 0;
-
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-err_mmu_notifier:
-	vhost_dev_free_iovecs(dev);
-#endif
 err_cgroup:
 	kthread_stop(worker);
 	dev->worker = NULL;
@@ -826,107 +654,6 @@ static void vhost_clear_msg(struct vhost_dev *dev)
 	spin_unlock(&dev->iotlb_lock);
 }
 
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-static void vhost_setup_uaddr(struct vhost_virtqueue *vq,
-			      int index, unsigned long uaddr,
-			      size_t size, bool write)
-{
-	struct vhost_uaddr *addr = &vq->uaddrs[index];
-
-	addr->uaddr = uaddr;
-	addr->size = size;
-	addr->write = write;
-}
-
-static void vhost_setup_vq_uaddr(struct vhost_virtqueue *vq)
-{
-	vhost_setup_uaddr(vq, VHOST_ADDR_DESC,
-			  (unsigned long)vq->desc,
-			  vhost_get_desc_size(vq, vq->num),
-			  false);
-	vhost_setup_uaddr(vq, VHOST_ADDR_AVAIL,
-			  (unsigned long)vq->avail,
-			  vhost_get_avail_size(vq, vq->num),
-			  false);
-	vhost_setup_uaddr(vq, VHOST_ADDR_USED,
-			  (unsigned long)vq->used,
-			  vhost_get_used_size(vq, vq->num),
-			  true);
-}
-
-static int vhost_map_prefetch(struct vhost_virtqueue *vq,
-			       int index)
-{
-	struct vhost_map *map;
-	struct vhost_uaddr *uaddr = &vq->uaddrs[index];
-	struct page **pages;
-	int npages = DIV_ROUND_UP(uaddr->size, PAGE_SIZE);
-	int npinned;
-	void *vaddr, *v;
-	int err;
-	int i;
-
-	spin_lock(&vq->mmu_lock);
-
-	err = -EFAULT;
-	if (vq->invalidate_count)
-		goto err;
-
-	err = -ENOMEM;
-	map = kmalloc(sizeof(*map), GFP_ATOMIC);
-	if (!map)
-		goto err;
-
-	pages = kmalloc_array(npages, sizeof(struct page *), GFP_ATOMIC);
-	if (!pages)
-		goto err_pages;
-
-	err = EFAULT;
-	npinned = __get_user_pages_fast(uaddr->uaddr, npages,
-					uaddr->write, pages);
-	if (npinned > 0)
-		release_pages(pages, npinned);
-	if (npinned != npages)
-		goto err_gup;
-
-	for (i = 0; i < npinned; i++)
-		if (PageHighMem(pages[i]))
-			goto err_gup;
-
-	vaddr = v = page_address(pages[0]);
-
-	/* For simplicity, fallback to userspace address if VA is not
-	 * contigious.
-	 */
-	for (i = 1; i < npinned; i++) {
-		v += PAGE_SIZE;
-		if (v != page_address(pages[i]))
-			goto err_gup;
-	}
-
-	map->addr = vaddr + (uaddr->uaddr & (PAGE_SIZE - 1));
-	map->npages = npages;
-	map->pages = pages;
-
-	rcu_assign_pointer(vq->maps[index], map);
-	/* No need for a synchronize_rcu(). This function should be
-	 * called by dev->worker so we are serialized with all
-	 * readers.
-	 */
-	spin_unlock(&vq->mmu_lock);
-
-	return 0;
-
-err_gup:
-	kfree(pages);
-err_pages:
-	kfree(map);
-err:
-	spin_unlock(&vq->mmu_lock);
-	return err;
-}
-#endif
-
 void vhost_dev_cleanup(struct vhost_dev *dev)
 {
 	int i;
@@ -956,16 +683,8 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
 		kthread_stop(dev->worker);
 		dev->worker = NULL;
 	}
-	if (dev->mm) {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-		mmu_notifier_unregister(&dev->mmu_notifier, dev->mm);
-#endif
+	if (dev->mm)
 		mmput(dev->mm);
-	}
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	for (i = 0; i < dev->nvqs; i++)
-		vhost_uninit_vq_maps(dev->vqs[i]);
-#endif
 	dev->mm = NULL;
 }
 EXPORT_SYMBOL_GPL(vhost_dev_cleanup);
@@ -1194,26 +913,6 @@ static inline void __user *__vhost_get_user(struct vhost_virtqueue *vq,
 
 static inline int vhost_put_avail_event(struct vhost_virtqueue *vq)
 {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	struct vhost_map *map;
-	struct vring_used *used;
-
-	if (!vq->iotlb) {
-		rcu_read_lock();
-
-		map = rcu_dereference(vq->maps[VHOST_ADDR_USED]);
-		if (likely(map)) {
-			used = map->addr;
-			*((__virtio16 *)&used->ring[vq->num]) =
-				cpu_to_vhost16(vq, vq->avail_idx);
-			rcu_read_unlock();
-			return 0;
-		}
-
-		rcu_read_unlock();
-	}
-#endif
-
 	return vhost_put_user(vq, cpu_to_vhost16(vq, vq->avail_idx),
 			      vhost_avail_event(vq));
 }
@@ -1222,27 +921,6 @@ static inline int vhost_put_used(struct vhost_virtqueue *vq,
 				 struct vring_used_elem *head, int idx,
 				 int count)
 {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	struct vhost_map *map;
-	struct vring_used *used;
-	size_t size;
-
-	if (!vq->iotlb) {
-		rcu_read_lock();
-
-		map = rcu_dereference(vq->maps[VHOST_ADDR_USED]);
-		if (likely(map)) {
-			used = map->addr;
-			size = count * sizeof(*head);
-			memcpy(used->ring + idx, head, size);
-			rcu_read_unlock();
-			return 0;
-		}
-
-		rcu_read_unlock();
-	}
-#endif
-
 	return vhost_copy_to_user(vq, vq->used->ring + idx, head,
 				  count * sizeof(*head));
 }
@@ -1250,25 +928,6 @@ static inline int vhost_put_used(struct vhost_virtqueue *vq,
 static inline int vhost_put_used_flags(struct vhost_virtqueue *vq)
 
 {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	struct vhost_map *map;
-	struct vring_used *used;
-
-	if (!vq->iotlb) {
-		rcu_read_lock();
-
-		map = rcu_dereference(vq->maps[VHOST_ADDR_USED]);
-		if (likely(map)) {
-			used = map->addr;
-			used->flags = cpu_to_vhost16(vq, vq->used_flags);
-			rcu_read_unlock();
-			return 0;
-		}
-
-		rcu_read_unlock();
-	}
-#endif
-
 	return vhost_put_user(vq, cpu_to_vhost16(vq, vq->used_flags),
 			      &vq->used->flags);
 }
@@ -1276,25 +935,6 @@ static inline int vhost_put_used_flags(struct vhost_virtqueue *vq)
 static inline int vhost_put_used_idx(struct vhost_virtqueue *vq)
 
 {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	struct vhost_map *map;
-	struct vring_used *used;
-
-	if (!vq->iotlb) {
-		rcu_read_lock();
-
-		map = rcu_dereference(vq->maps[VHOST_ADDR_USED]);
-		if (likely(map)) {
-			used = map->addr;
-			used->idx = cpu_to_vhost16(vq, vq->last_used_idx);
-			rcu_read_unlock();
-			return 0;
-		}
-
-		rcu_read_unlock();
-	}
-#endif
-
 	return vhost_put_user(vq, cpu_to_vhost16(vq, vq->last_used_idx),
 			      &vq->used->idx);
 }
@@ -1340,50 +980,12 @@ static void vhost_dev_unlock_vqs(struct vhost_dev *d)
 static inline int vhost_get_avail_idx(struct vhost_virtqueue *vq,
 				      __virtio16 *idx)
 {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	struct vhost_map *map;
-	struct vring_avail *avail;
-
-	if (!vq->iotlb) {
-		rcu_read_lock();
-
-		map = rcu_dereference(vq->maps[VHOST_ADDR_AVAIL]);
-		if (likely(map)) {
-			avail = map->addr;
-			*idx = avail->idx;
-			rcu_read_unlock();
-			return 0;
-		}
-
-		rcu_read_unlock();
-	}
-#endif
-
 	return vhost_get_avail(vq, *idx, &vq->avail->idx);
 }
 
 static inline int vhost_get_avail_head(struct vhost_virtqueue *vq,
 				       __virtio16 *head, int idx)
 {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	struct vhost_map *map;
-	struct vring_avail *avail;
-
-	if (!vq->iotlb) {
-		rcu_read_lock();
-
-		map = rcu_dereference(vq->maps[VHOST_ADDR_AVAIL]);
-		if (likely(map)) {
-			avail = map->addr;
-			*head = avail->ring[idx & (vq->num - 1)];
-			rcu_read_unlock();
-			return 0;
-		}
-
-		rcu_read_unlock();
-	}
-#endif
-
 	return vhost_get_avail(vq, *head,
 			       &vq->avail->ring[idx & (vq->num - 1)]);
 }
@@ -1391,98 +993,24 @@ static inline int vhost_get_avail_head(struct vhost_virtqueue *vq,
 static inline int vhost_get_avail_flags(struct vhost_virtqueue *vq,
 					__virtio16 *flags)
 {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	struct vhost_map *map;
-	struct vring_avail *avail;
-
-	if (!vq->iotlb) {
-		rcu_read_lock();
-
-		map = rcu_dereference(vq->maps[VHOST_ADDR_AVAIL]);
-		if (likely(map)) {
-			avail = map->addr;
-			*flags = avail->flags;
-			rcu_read_unlock();
-			return 0;
-		}
-
-		rcu_read_unlock();
-	}
-#endif
-
 	return vhost_get_avail(vq, *flags, &vq->avail->flags);
 }
 
 static inline int vhost_get_used_event(struct vhost_virtqueue *vq,
 				       __virtio16 *event)
 {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	struct vhost_map *map;
-	struct vring_avail *avail;
-
-	if (!vq->iotlb) {
-		rcu_read_lock();
-		map = rcu_dereference(vq->maps[VHOST_ADDR_AVAIL]);
-		if (likely(map)) {
-			avail = map->addr;
-			*event = (__virtio16)avail->ring[vq->num];
-			rcu_read_unlock();
-			return 0;
-		}
-		rcu_read_unlock();
-	}
-#endif
-
 	return vhost_get_avail(vq, *event, vhost_used_event(vq));
 }
 
 static inline int vhost_get_used_idx(struct vhost_virtqueue *vq,
 				     __virtio16 *idx)
 {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	struct vhost_map *map;
-	struct vring_used *used;
-
-	if (!vq->iotlb) {
-		rcu_read_lock();
-
-		map = rcu_dereference(vq->maps[VHOST_ADDR_USED]);
-		if (likely(map)) {
-			used = map->addr;
-			*idx = used->idx;
-			rcu_read_unlock();
-			return 0;
-		}
-
-		rcu_read_unlock();
-	}
-#endif
-
 	return vhost_get_used(vq, *idx, &vq->used->idx);
 }
 
 static inline int vhost_get_desc(struct vhost_virtqueue *vq,
 				 struct vring_desc *desc, int idx)
 {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	struct vhost_map *map;
-	struct vring_desc *d;
-
-	if (!vq->iotlb) {
-		rcu_read_lock();
-
-		map = rcu_dereference(vq->maps[VHOST_ADDR_DESC]);
-		if (likely(map)) {
-			d = map->addr;
-			*desc = *(d + idx);
-			rcu_read_unlock();
-			return 0;
-		}
-
-		rcu_read_unlock();
-	}
-#endif
-
 	return vhost_copy_from_user(vq, desc, vq->desc + idx, sizeof(*desc));
 }
 
@@ -1823,32 +1351,12 @@ static bool iotlb_access_ok(struct vhost_virtqueue *vq,
 	return true;
 }
 
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-static void vhost_vq_map_prefetch(struct vhost_virtqueue *vq)
-{
-	struct vhost_map __rcu *map;
-	int i;
-
-	for (i = 0; i < VHOST_NUM_ADDRS; i++) {
-		rcu_read_lock();
-		map = rcu_dereference(vq->maps[i]);
-		rcu_read_unlock();
-		if (unlikely(!map))
-			vhost_map_prefetch(vq, i);
-	}
-}
-#endif
-
 int vq_meta_prefetch(struct vhost_virtqueue *vq)
 {
 	unsigned int num = vq->num;
 
-	if (!vq->iotlb) {
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-		vhost_vq_map_prefetch(vq);
-#endif
+	if (!vq->iotlb)
 		return 1;
-	}
 
 	return iotlb_access_ok(vq, VHOST_ACCESS_RO, (u64)(uintptr_t)vq->desc,
 			       vhost_get_desc_size(vq, num), VHOST_ADDR_DESC) &&
@@ -2059,16 +1567,6 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d,
 
 	mutex_lock(&vq->mutex);
 
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	/* Unregister MMU notifer to allow invalidation callback
-	 * can access vq->uaddrs[] without holding a lock.
-	 */
-	if (d->mm)
-		mmu_notifier_unregister(&d->mmu_notifier, d->mm);
-
-	vhost_uninit_vq_maps(vq);
-#endif
-
 	switch (ioctl) {
 	case VHOST_SET_VRING_NUM:
 		r = vhost_vring_set_num(d, vq, argp);
@@ -2080,13 +1578,6 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d,
 		BUG();
 	}
 
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	vhost_setup_vq_uaddr(vq);
-
-	if (d->mm)
-		mmu_notifier_register(&d->mmu_notifier, d->mm);
-#endif
-
 	mutex_unlock(&vq->mutex);
 
 	return r;

drivers/vhost/vhost.h

@@ -12,9 +12,6 @@
 #include <linux/virtio_config.h>
 #include <linux/virtio_ring.h>
 #include <linux/atomic.h>
-#include <linux/pagemap.h>
-#include <linux/mmu_notifier.h>
-#include <asm/cacheflush.h>
 
 struct vhost_work;
 typedef void (*vhost_work_fn_t)(struct vhost_work *work);
@@ -83,24 +80,6 @@ enum vhost_uaddr_type {
 	VHOST_NUM_ADDRS = 3,
 };
 
-struct vhost_map {
-	int npages;
-	void *addr;
-	struct page **pages;
-};
-
-struct vhost_uaddr {
-	unsigned long uaddr;
-	size_t size;
-	bool write;
-};
-
-#if defined(CONFIG_MMU_NOTIFIER) && ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE == 0
-#define VHOST_ARCH_CAN_ACCEL_UACCESS 0
-#else
-#define VHOST_ARCH_CAN_ACCEL_UACCESS 0
-#endif
-
 /* The virtqueue structure describes a queue attached to a device. */
 struct vhost_virtqueue {
 	struct vhost_dev *dev;
@@ -111,22 +90,7 @@ struct vhost_virtqueue {
 	struct vring_desc __user *desc;
 	struct vring_avail __user *avail;
 	struct vring_used __user *used;
-
-#if VHOST_ARCH_CAN_ACCEL_UACCESS
-	/* Read by memory accessors, modified by meta data
-	 * prefetching, MMU notifier and vring ioctl().
-	 * Synchonrized through mmu_lock (writers) and RCU (writers
-	 * and readers).
-	 */
-	struct vhost_map __rcu *maps[VHOST_NUM_ADDRS];
-	/* Read by MMU notifier, modified by vring ioctl(),
-	 * synchronized through MMU notifier
-	 * registering/unregistering.
-	 */
-	struct vhost_uaddr uaddrs[VHOST_NUM_ADDRS];
-#endif
 	const struct vhost_umem_node *meta_iotlb[VHOST_NUM_ADDRS];
-
 	struct file *kick;
 	struct eventfd_ctx *call_ctx;
 	struct eventfd_ctx *error_ctx;
@@ -181,8 +145,6 @@ struct vhost_virtqueue {
 	bool user_be;
 #endif
 	u32 busyloop_timeout;
-	spinlock_t mmu_lock;
-	int invalidate_count;
 };
 
 struct vhost_msg_node {
@@ -196,9 +158,6 @@ struct vhost_msg_node {
 
 struct vhost_dev {
 	struct mm_struct *mm;
-#ifdef CONFIG_MMU_NOTIFIER
-	struct mmu_notifier mmu_notifier;
-#endif
 	struct mutex mutex;
 	struct vhost_virtqueue **vqs;
 	int nvqs;