vhost: access vq metadata through kernel virtual address

It was noticed that the copy_to/from_user() friends that was used to access virtqueue metdata tends to be very expensive for dataplane implementation like vhost since it involves lots of software checks, speculation barriers, hardware feature toggling (e.g SMAP). The extra cost will be more obvious when transferring small packets since the time spent on metadata accessing become more significant. This patch tries to eliminate those overheads by accessing them through direct mapping of those pages. Invalidation callbacks is implemented for co-operation with general VM management (swap, KSM, THP or NUMA balancing). We will try to get the direct mapping of vq metadata before each round of packet processing if it doesn't exist. If we fail, we will simplely fallback to copy_to/from_user() friends. This invalidation and direct mapping access are synchronized through spinlock and RCU. All matedata accessing through direct map is protected by RCU, and the setup or invalidation are done under spinlock. This method might does not work for high mem page which requires temporary mapping so we just fallback to normal copy_to/from_user() and may not for arch that has virtual tagged cache since extra cache flushing is needed to eliminate the alias. This will result complex logic and bad performance. For those archs, this patch simply go for copy_to/from_user() friends. This is done by ruling out kernel mapping codes through ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE. Note that this is only done when device IOTLB is not enabled. We could use similar method to optimize IOTLB in the future. Tests shows at most about 23% improvement on TX PPS when using virtio-user + vhost_net + xdp1 + TAP on 2.6GHz Broadwell: SMAP on | SMAP off Before: 5.2Mpps | 7.1Mpps After: 6.4Mpps | 8.2Mpps Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: James Bottomley <James.Bottomley@hansenpartnership.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Miller <davem@davemloft.net> Cc: Jerome Glisse <jglisse@redhat.com> Cc: linux-mm@kvack.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-parisc@vger.kernel.org Signed-off-by: Jason Wang <jasowang@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-05-24 04:12:18 -04:00 · 2019-05-24 04:12:18 -04:00 · 7f466032dc
parent feebcaeac7
commit 7f466032dc
2 changed files with 550 additions and 3 deletions
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@ -299,6 +299,160 @@ 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)
 {
@ -327,7 +481,11 @@ 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)
@ -477,7 +635,9 @@ 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];
@ -486,6 +646,7 @@ 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,
@ -565,7 +726,18 @@ 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;
@ -656,6 +828,107 @@ 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;
@ -685,8 +958,16 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
 		kthread_stop(dev->worker);
 		dev->worker = NULL;
 	}
-	if (dev->mm)
+	if (dev->mm) {
+#if VHOST_ARCH_CAN_ACCEL_UACCESS
+		mmu_notifier_unregister(&dev->mmu_notifier, dev->mm);
+#endif
 		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);
@ -915,6 +1196,26 @@ 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));
 }
@ -923,6 +1224,27 @@ 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));
 }
@ -930,6 +1252,25 @@ 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);
 }
@ -937,6 +1278,25 @@ 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);
 }
@ -982,12 +1342,50 @@ 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)]);
 }
@ -995,24 +1393,98 @@ 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));
 }

@ -1353,12 +1825,32 @@ 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 (!vq->iotlb) {
+#if VHOST_ARCH_CAN_ACCEL_UACCESS
+		vhost_vq_map_prefetch(vq);
+#endif
 		return 1;
+	}

 	return iotlb_access_ok(vq, VHOST_ACCESS_RO, (u64)(uintptr_t)vq->desc,
 			       vhost_get_desc_size(vq, num), VHOST_ADDR_DESC) &&
@ -1569,6 +2061,16 @@ 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);
@ -1580,6 +2082,13 @@ 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;
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@ -12,6 +12,9 @@
 #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);
@ -80,6 +83,21 @@ 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;
+};
+
+#define VHOST_ARCH_CAN_ACCEL_UACCESS defined(CONFIG_MMU_NOTIFIER) && \
+	ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE == 0
+
 /* The virtqueue structure describes a queue attached to a device. */
 struct vhost_virtqueue {
 	struct vhost_dev *dev;
@ -90,7 +108,22 @@ 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;
@ -145,6 +178,8 @@ struct vhost_virtqueue {
 	bool user_be;
 #endif
 	u32 busyloop_timeout;
+	spinlock_t mmu_lock;
+	int invalidate_count;
 };

 struct vhost_msg_node {
@ -158,6 +193,9 @@ 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;