vhost: new device IOTLB API

This patch tries to implement an device IOTLB for vhost. This could be
used with userspace(qemu) implementation of DMA remapping
to emulate an IOMMU for the guest.

The idea is simple, cache the translation in a software device IOTLB
(which is implemented as an interval tree) in vhost and use vhost_net
file descriptor for reporting IOTLB miss and IOTLB
update/invalidation. When vhost meets an IOTLB miss, the fault
address, size and access can be read from the file. After userspace
finishes the translation, it writes the translated address to the
vhost_net file to update the device IOTLB.

When device IOTLB is enabled by setting VIRTIO_F_IOMMU_PLATFORM all vq
addresses set by ioctl are treated as iova instead of virtual address and
the accessing can only be done through IOTLB instead of direct userspace
memory access. Before each round or vq processing, all vq metadata is
prefetched in device IOTLB to make sure no translation fault happens
during vq processing.

In most cases, virtqueues are contiguous even in virtual address space.
The IOTLB translation for virtqueue itself may make it a little
slower. We might add fast path cache on top of this patch.

Signed-off-by: Jason Wang <jasowang@redhat.com>
[mst: use virtio feature bit: VHOST_F_DEVICE_IOTLB -> VIRTIO_F_IOMMU_PLATFORM ]
[mst: fix build warnings ]
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
[ weiyj.lk: missing unlock on error ]
Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>

1 files changed, 593 insertions, 43 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 8071f3638db9..d02c1614921f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -35,6 +35,10 @@ static ushort max_mem_regions = 64;
 module_param(max_mem_regions, ushort, 0444);
 MODULE_PARM_DESC(max_mem_regions,
 	"Maximum number of memory regions in memory map. (default: 64)");
+static int max_iotlb_entries = 2048;
+module_param(max_iotlb_entries, int, 0444);
+MODULE_PARM_DESC(max_iotlb_entries,
+	"Maximum number of iotlb entries. (default: 2048)");
 
 enum {
 	VHOST_MEMORY_F_LOG = 0x1,
@@ -306,6 +310,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 	vhost_disable_cross_endian(vq);
 	vq->busyloop_timeout = 0;
 	vq->umem = NULL;
+	vq->iotlb = NULL;
 }
 
 static int vhost_worker(void *data)
@@ -400,9 +405,14 @@ void vhost_dev_init(struct vhost_dev *dev,
 	dev->log_ctx = NULL;
 	dev->log_file = NULL;
 	dev->umem = NULL;
+	dev->iotlb = NULL;
 	dev->mm = NULL;
 	dev->worker = NULL;
 	init_llist_head(&dev->work_list);
+	init_waitqueue_head(&dev->wait);
+	INIT_LIST_HEAD(&dev->read_list);
+	INIT_LIST_HEAD(&dev->pending_list);
+	spin_lock_init(&dev->iotlb_lock);
 
 
 	for (i = 0; i < dev->nvqs; ++i) {
@@ -550,6 +560,15 @@ void vhost_dev_stop(struct vhost_dev *dev)
 }
 EXPORT_SYMBOL_GPL(vhost_dev_stop);
 
+static void vhost_umem_free(struct vhost_umem *umem,
+			    struct vhost_umem_node *node)
+{
+	vhost_umem_interval_tree_remove(node, &umem->umem_tree);
+	list_del(&node->link);
+	kfree(node);
+	umem->numem--;
+}
+
 static void vhost_umem_clean(struct vhost_umem *umem)
 {
 	struct vhost_umem_node *node, *tmp;
@@ -557,14 +576,31 @@ static void vhost_umem_clean(struct vhost_umem *umem)
 	if (!umem)
 		return;
 
-	list_for_each_entry_safe(node, tmp, &umem->umem_list, link) {
-		vhost_umem_interval_tree_remove(node, &umem->umem_tree);
-		list_del(&node->link);
-		kvfree(node);
-	}
+	list_for_each_entry_safe(node, tmp, &umem->umem_list, link)
+		vhost_umem_free(umem, node);
+
 	kvfree(umem);
 }
 
+static void vhost_clear_msg(struct vhost_dev *dev)
+{
+	struct vhost_msg_node *node, *n;
+
+	spin_lock(&dev->iotlb_lock);
+
+	list_for_each_entry_safe(node, n, &dev->read_list, node) {
+		list_del(&node->node);
+		kfree(node);
+	}
+
+	list_for_each_entry_safe(node, n, &dev->pending_list, node) {
+		list_del(&node->node);
+		kfree(node);
+	}
+
+	spin_unlock(&dev->iotlb_lock);
+}
+
 /* Caller should have device mutex if and only if locked is set */
 void vhost_dev_cleanup(struct vhost_dev *dev, bool locked)
 {
@@ -593,6 +629,10 @@ void vhost_dev_cleanup(struct vhost_dev *dev, bool locked)
 	/* No one will access memory at this point */
 	vhost_umem_clean(dev->umem);
 	dev->umem = NULL;
+	vhost_umem_clean(dev->iotlb);
+	dev->iotlb = NULL;
+	vhost_clear_msg(dev);
+	wake_up_interruptible_poll(&dev->wait, POLLIN | POLLRDNORM);
 	WARN_ON(!llist_empty(&dev->work_list));
 	if (dev->worker) {
 		kthread_stop(dev->worker);
@@ -668,28 +708,381 @@ static int memory_access_ok(struct vhost_dev *d, struct vhost_umem *umem,
 	return 1;
 }
 
-#define vhost_put_user(vq, x, ptr)  __put_user(x, ptr)
+static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
+			  struct iovec iov[], int iov_size, int access);
 
 static int vhost_copy_to_user(struct vhost_virtqueue *vq, void *to,
 			      const void *from, unsigned size)
 {
-	return __copy_to_user(to, from, size);
-}
+	int ret;
 
-#define vhost_get_user(vq, x, ptr) __get_user(x, ptr)
+	if (!vq->iotlb)
+		return __copy_to_user(to, from, size);
+	else {
+		/* This function should be called after iotlb
+		 * prefetch, which means we're sure that all vq
+		 * could be access through iotlb. So -EAGAIN should
+		 * not happen in this case.
+		 */
+		/* TODO: more fast path */
+		struct iov_iter t;
+		ret = translate_desc(vq, (u64)(uintptr_t)to, size, vq->iotlb_iov,
+				     ARRAY_SIZE(vq->iotlb_iov),
+				     VHOST_ACCESS_WO);
+		if (ret < 0)
+			goto out;
+		iov_iter_init(&t, WRITE, vq->iotlb_iov, ret, size);
+		ret = copy_to_iter(from, size, &t);
+		if (ret == size)
+			ret = 0;
+	}
+out:
+	return ret;
+}
 
 static int vhost_copy_from_user(struct vhost_virtqueue *vq, void *to,
 				void *from, unsigned size)
 {
-	return __copy_from_user(to, from, size);
+	int ret;
+
+	if (!vq->iotlb)
+		return __copy_from_user(to, from, size);
+	else {
+		/* This function should be called after iotlb
+		 * prefetch, which means we're sure that vq
+		 * could be access through iotlb. So -EAGAIN should
+		 * not happen in this case.
+		 */
+		/* TODO: more fast path */
+		struct iov_iter f;
+		ret = translate_desc(vq, (u64)(uintptr_t)from, size, vq->iotlb_iov,
+				     ARRAY_SIZE(vq->iotlb_iov),
+				     VHOST_ACCESS_RO);
+		if (ret < 0) {
+			vq_err(vq, "IOTLB translation failure: uaddr "
+			       "%p size 0x%llx\n", from,
+			       (unsigned long long) size);
+			goto out;
+		}
+		iov_iter_init(&f, READ, vq->iotlb_iov, ret, size);
+		ret = copy_from_iter(to, size, &f);
+		if (ret == size)
+			ret = 0;
+	}
+
+out:
+	return ret;
+}
+
+static void __user *__vhost_get_user(struct vhost_virtqueue *vq,
+				     void *addr, unsigned size)
+{
+	int ret;
+
+	/* This function should be called after iotlb
+	 * prefetch, which means we're sure that vq
+	 * could be access through iotlb. So -EAGAIN should
+	 * not happen in this case.
+	 */
+	/* TODO: more fast path */
+	ret = translate_desc(vq, (u64)(uintptr_t)addr, size, vq->iotlb_iov,
+			     ARRAY_SIZE(vq->iotlb_iov),
+			     VHOST_ACCESS_RO);
+	if (ret < 0) {
+		vq_err(vq, "IOTLB translation failure: uaddr "
+			"%p size 0x%llx\n", addr,
+			(unsigned long long) size);
+		return NULL;
+	}
+
+	if (ret != 1 || vq->iotlb_iov[0].iov_len != size) {
+		vq_err(vq, "Non atomic userspace memory access: uaddr "
+			"%p size 0x%llx\n", addr,
+			(unsigned long long) size);
+		return NULL;
+	}
+
+	return vq->iotlb_iov[0].iov_base;
+}
+
+#define vhost_put_user(vq, x, ptr) \
+({ \
+	int ret = -EFAULT; \
+	if (!vq->iotlb) { \
+		ret = __put_user(x, ptr); \
+	} else { \
+		__typeof__(ptr) to = \
+			(__typeof__(ptr)) __vhost_get_user(vq, ptr, sizeof(*ptr)); \
+		if (to != NULL) \
+			ret = __put_user(x, to); \
+		else \
+			ret = -EFAULT;	\
+	} \
+	ret; \
+})
+
+#define vhost_get_user(vq, x, ptr) \
+({ \
+	int ret; \
+	if (!vq->iotlb) { \
+		ret = __get_user(x, ptr); \
+	} else { \
+		__typeof__(ptr) from = \
+			(__typeof__(ptr)) __vhost_get_user(vq, ptr, sizeof(*ptr)); \
+		if (from != NULL) \
+			ret = __get_user(x, from); \
+		else \
+			ret = -EFAULT; \
+	} \
+	ret; \
+})
+
+static void vhost_dev_lock_vqs(struct vhost_dev *d)
+{
+	int i = 0;
+	for (i = 0; i < d->nvqs; ++i)
+		mutex_lock(&d->vqs[i]->mutex);
+}
+
+static void vhost_dev_unlock_vqs(struct vhost_dev *d)
+{
+	int i = 0;
+	for (i = 0; i < d->nvqs; ++i)
+		mutex_unlock(&d->vqs[i]->mutex);
+}
+
+static int vhost_new_umem_range(struct vhost_umem *umem,
+				u64 start, u64 size, u64 end,
+				u64 userspace_addr, int perm)
+{
+	struct vhost_umem_node *tmp, *node = kmalloc(sizeof(*node), GFP_ATOMIC);
+
+	if (!node)
+		return -ENOMEM;
+
+	if (umem->numem == max_iotlb_entries) {
+		tmp = list_first_entry(&umem->umem_list, typeof(*tmp), link);
+		vhost_umem_free(umem, tmp);
+	}
+
+	node->start = start;
+	node->size = size;
+	node->last = end;
+	node->userspace_addr = userspace_addr;
+	node->perm = perm;
+	INIT_LIST_HEAD(&node->link);
+	list_add_tail(&node->link, &umem->umem_list);
+	vhost_umem_interval_tree_insert(node, &umem->umem_tree);
+	umem->numem++;
+
+	return 0;
+}
+
+static void vhost_del_umem_range(struct vhost_umem *umem,
+				 u64 start, u64 end)
+{
+	struct vhost_umem_node *node;
+
+	while ((node = vhost_umem_interval_tree_iter_first(&umem->umem_tree,
+							   start, end)))
+		vhost_umem_free(umem, node);
+}
+
+static void vhost_iotlb_notify_vq(struct vhost_dev *d,
+				  struct vhost_iotlb_msg *msg)
+{
+	struct vhost_msg_node *node, *n;
+
+	spin_lock(&d->iotlb_lock);
+
+	list_for_each_entry_safe(node, n, &d->pending_list, node) {
+		struct vhost_iotlb_msg *vq_msg = &node->msg.iotlb;
+		if (msg->iova <= vq_msg->iova &&
+		    msg->iova + msg->size - 1 > vq_msg->iova &&
+		    vq_msg->type == VHOST_IOTLB_MISS) {
+			vhost_poll_queue(&node->vq->poll);
+			list_del(&node->node);
+			kfree(node);
+		}
+	}
+
+	spin_unlock(&d->iotlb_lock);
+}
+
+static int umem_access_ok(u64 uaddr, u64 size, int access)
+{
+	unsigned long a = uaddr;
+
+	if ((access & VHOST_ACCESS_RO) &&
+	    !access_ok(VERIFY_READ, (void __user *)a, size))
+		return -EFAULT;
+	if ((access & VHOST_ACCESS_WO) &&
+	    !access_ok(VERIFY_WRITE, (void __user *)a, size))
+		return -EFAULT;
+	return 0;
+}
+
+int vhost_process_iotlb_msg(struct vhost_dev *dev,
+			    struct vhost_iotlb_msg *msg)
+{
+	int ret = 0;
+
+	vhost_dev_lock_vqs(dev);
+	switch (msg->type) {
+	case VHOST_IOTLB_UPDATE:
+		if (!dev->iotlb) {
+			ret = -EFAULT;
+			break;
+		}
+		if (umem_access_ok(msg->uaddr, msg->size, msg->perm)) {
+			ret = -EFAULT;
+			break;
+		}
+		if (vhost_new_umem_range(dev->iotlb, msg->iova, msg->size,
+					 msg->iova + msg->size - 1,
+					 msg->uaddr, msg->perm)) {
+			ret = -ENOMEM;
+			break;
+		}
+		vhost_iotlb_notify_vq(dev, msg);
+		break;
+	case VHOST_IOTLB_INVALIDATE:
+		vhost_del_umem_range(dev->iotlb, msg->iova,
+				     msg->iova + msg->size - 1);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	vhost_dev_unlock_vqs(dev);
+	return ret;
+}
+ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
+			     struct iov_iter *from)
+{
+	struct vhost_msg_node node;
+	unsigned size = sizeof(struct vhost_msg);
+	size_t ret;
+	int err;
+
+	if (iov_iter_count(from) < size)
+		return 0;
+	ret = copy_from_iter(&node.msg, size, from);
+	if (ret != size)
+		goto done;
+
+	switch (node.msg.type) {
+	case VHOST_IOTLB_MSG:
+		err = vhost_process_iotlb_msg(dev, &node.msg.iotlb);
+		if (err)
+			ret = err;
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+done:
+	return ret;
+}
+EXPORT_SYMBOL(vhost_chr_write_iter);
+
+unsigned int vhost_chr_poll(struct file *file, struct vhost_dev *dev,
+			    poll_table *wait)
+{
+	unsigned int mask = 0;
+
+	poll_wait(file, &dev->wait, wait);
+
+	if (!list_empty(&dev->read_list))
+		mask |= POLLIN | POLLRDNORM;
+
+	return mask;
+}
+EXPORT_SYMBOL(vhost_chr_poll);
+
+ssize_t vhost_chr_read_iter(struct vhost_dev *dev, struct iov_iter *to,
+			    int noblock)
+{
+	DEFINE_WAIT(wait);
+	struct vhost_msg_node *node;
+	ssize_t ret = 0;
+	unsigned size = sizeof(struct vhost_msg);
+
+	if (iov_iter_count(to) < size)
+		return 0;
+
+	while (1) {
+		if (!noblock)
+			prepare_to_wait(&dev->wait, &wait,
+					TASK_INTERRUPTIBLE);
+
+		node = vhost_dequeue_msg(dev, &dev->read_list);
+		if (node)
+			break;
+		if (noblock) {
+			ret = -EAGAIN;
+			break;
+		}
+		if (signal_pending(current)) {
+			ret = -ERESTARTSYS;
+			break;
+		}
+		if (!dev->iotlb) {
+			ret = -EBADFD;
+			break;
+		}
+
+		schedule();
+	}
+
+	if (!noblock)
+		finish_wait(&dev->wait, &wait);
+
+	if (node) {
+		ret = copy_to_iter(&node->msg, size, to);
+
+		if (ret != size || node->msg.type != VHOST_IOTLB_MISS) {
+			kfree(node);
+			return ret;
+		}
+
+		vhost_enqueue_msg(dev, &dev->pending_list, node);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(vhost_chr_read_iter);
+
+static int vhost_iotlb_miss(struct vhost_virtqueue *vq, u64 iova, int access)
+{
+	struct vhost_dev *dev = vq->dev;
+	struct vhost_msg_node *node;
+	struct vhost_iotlb_msg *msg;
+
+	node = vhost_new_msg(vq, VHOST_IOTLB_MISS);
+	if (!node)
+		return -ENOMEM;
+
+	msg = &node->msg.iotlb;
+	msg->type = VHOST_IOTLB_MISS;
+	msg->iova = iova;
+	msg->perm = access;
+
+	vhost_enqueue_msg(dev, &dev->read_list, node);
+
+	return 0;
 }
 
 static int vq_access_ok(struct vhost_virtqueue *vq, unsigned int num,
 			struct vring_desc __user *desc,
 			struct vring_avail __user *avail,
 			struct vring_used __user *used)
+
 {
 	size_t s = vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
+
 	return access_ok(VERIFY_READ, desc, num * sizeof *desc) &&
 	       access_ok(VERIFY_READ, avail,
 			 sizeof *avail + num * sizeof *avail->ring + s) &&
@@ -697,6 +1090,54 @@ static int vq_access_ok(struct vhost_virtqueue *vq, unsigned int num,
 			sizeof *used + num * sizeof *used->ring + s);
 }
 
+static int iotlb_access_ok(struct vhost_virtqueue *vq,
+			   int access, u64 addr, u64 len)
+{
+	const struct vhost_umem_node *node;
+	struct vhost_umem *umem = vq->iotlb;
+	u64 s = 0, size;
+
+	while (len > s) {
+		node = vhost_umem_interval_tree_iter_first(&umem->umem_tree,
+							   addr,
+							   addr + len - 1);
+		if (node == NULL || node->start > addr) {
+			vhost_iotlb_miss(vq, addr, access);
+			return false;
+		} else if (!(node->perm & access)) {
+			/* Report the possible access violation by
+			 * request another translation from userspace.
+			 */
+			return false;
+		}
+
+		size = node->size - addr + node->start;
+		s += size;
+		addr += size;
+	}
+
+	return true;
+}
+
+int vq_iotlb_prefetch(struct vhost_virtqueue *vq)
+{
+	size_t s = vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
+	unsigned int num = vq->num;
+
+	if (!vq->iotlb)
+		return 1;
+
+	return iotlb_access_ok(vq, VHOST_ACCESS_RO, (u64)(uintptr_t)vq->desc,
+			       num * sizeof *vq->desc) &&
+	       iotlb_access_ok(vq, VHOST_ACCESS_RO, (u64)(uintptr_t)vq->avail,
+			       sizeof *vq->avail +
+			       num * sizeof *vq->avail->ring + s) &&
+	       iotlb_access_ok(vq, VHOST_ACCESS_WO, (u64)(uintptr_t)vq->used,
+			       sizeof *vq->used +
+			       num * sizeof *vq->used->ring + s);
+}
+EXPORT_SYMBOL_GPL(vq_iotlb_prefetch);
+
 /* Can we log writes? */
 /* Caller should have device mutex but not vq mutex */
 int vhost_log_access_ok(struct vhost_dev *dev)
@@ -723,16 +1164,35 @@ static int vq_log_access_ok(struct vhost_virtqueue *vq,
 /* Caller should have vq mutex and device mutex */
 int vhost_vq_access_ok(struct vhost_virtqueue *vq)
 {
+	if (vq->iotlb) {
+		/* When device IOTLB was used, the access validation
+		 * will be validated during prefetching.
+		 */
+		return 1;
+	}
 	return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used) &&
 		vq_log_access_ok(vq, vq->log_base);
 }
 EXPORT_SYMBOL_GPL(vhost_vq_access_ok);
 
+static struct vhost_umem *vhost_umem_alloc(void)
+{
+	struct vhost_umem *umem = vhost_kvzalloc(sizeof(*umem));
+
+	if (!umem)
+		return NULL;
+
+	umem->umem_tree = RB_ROOT;
+	umem->numem = 0;
+	INIT_LIST_HEAD(&umem->umem_list);
+
+	return umem;
+}
+
 static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 {
 	struct vhost_memory mem, *newmem;
 	struct vhost_memory_region *region;
-	struct vhost_umem_node *node;
 	struct vhost_umem *newumem, *oldumem;
 	unsigned long size = offsetof(struct vhost_memory, regions);
 	int i;
@@ -754,28 +1214,23 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 		return -EFAULT;
 	}
 
-	newumem = vhost_kvzalloc(sizeof(*newumem));
+	newumem = vhost_umem_alloc();
 	if (!newumem) {
 		kvfree(newmem);
 		return -ENOMEM;
 	}
 
-	newumem->umem_tree = RB_ROOT;
-	INIT_LIST_HEAD(&newumem->umem_list);
-
 	for (region = newmem->regions;
 	     region < newmem->regions + mem.nregions;
 	     region++) {
-		node = vhost_kvzalloc(sizeof(*node));
-		if (!node)
+		if (vhost_new_umem_range(newumem,
+					 region->guest_phys_addr,
+					 region->memory_size,
+					 region->guest_phys_addr +
+					 region->memory_size - 1,
+					 region->userspace_addr,
+					 VHOST_ACCESS_RW))
 			goto err;
-		node->start = region->guest_phys_addr;
-		node->size = region->memory_size;
-		node->last = node->start + node->size - 1;
-		node->userspace_addr = region->userspace_addr;
-		INIT_LIST_HEAD(&node->link);
-		list_add_tail(&node->link, &newumem->umem_list);
-		vhost_umem_interval_tree_insert(node, &newumem->umem_tree);
 	}
 
 	if (!memory_access_ok(d, newumem, 0))
@@ -1019,6 +1474,30 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
 }
 EXPORT_SYMBOL_GPL(vhost_vring_ioctl);
 
+int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
+{
+	struct vhost_umem *niotlb, *oiotlb;
+	int i;
+
+	niotlb = vhost_umem_alloc();
+	if (!niotlb)
+		return -ENOMEM;
+
+	oiotlb = d->iotlb;
+	d->iotlb = niotlb;
+
+	for (i = 0; i < d->nvqs; ++i) {
+		mutex_lock(&d->vqs[i]->mutex);
+		d->vqs[i]->iotlb = niotlb;
+		mutex_unlock(&d->vqs[i]->mutex);
+	}
+
+	vhost_umem_clean(oiotlb);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(vhost_init_device_iotlb);
+
 /* Caller must have device mutex */
 long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 {
@@ -1233,15 +1712,20 @@ int vhost_vq_init_access(struct vhost_virtqueue *vq)
 	if (r)
 		goto err;
 	vq->signalled_used_valid = false;
-	if (!access_ok(VERIFY_READ, &vq->used->idx, sizeof vq->used->idx)) {
+	if (!vq->iotlb &&
+	    !access_ok(VERIFY_READ, &vq->used->idx, sizeof vq->used->idx)) {
 		r = -EFAULT;
 		goto err;
 	}
 	r = vhost_get_user(vq, last_used_idx, &vq->used->idx);
-	if (r)
+	if (r) {
+		vq_err(vq, "Can't access used idx at %p\n",
+		       &vq->used->idx);
 		goto err;
+	}
 	vq->last_used_idx = vhost16_to_cpu(vq, last_used_idx);
 	return 0;
+
 err:
 	vq->is_le = is_le;
 	return r;
@@ -1249,10 +1733,11 @@ err:
 EXPORT_SYMBOL_GPL(vhost_vq_init_access);
 
 static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
-			  struct iovec iov[], int iov_size)
+			  struct iovec iov[], int iov_size, int access)
 {
 	const struct vhost_umem_node *node;
-	struct vhost_umem *umem = vq->umem;
+	struct vhost_dev *dev = vq->dev;
+	struct vhost_umem *umem = dev->iotlb ? dev->iotlb : dev->umem;
 	struct iovec *_iov;
 	u64 s = 0;
 	int ret = 0;
@@ -1263,12 +1748,21 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
 			ret = -ENOBUFS;
 			break;
 		}
+
 		node = vhost_umem_interval_tree_iter_first(&umem->umem_tree,
 							addr, addr + len - 1);
 		if (node == NULL || node->start > addr) {
-			ret = -EFAULT;
+			if (umem != dev->iotlb) {
+				ret = -EFAULT;
+				break;
+			}
+			ret = -EAGAIN;
+			break;
+		} else if (!(node->perm & access)) {
+			ret = -EPERM;
 			break;
 		}
+
 		_iov = iov + ret;
 		size = node->size - addr + node->start;
 		_iov->iov_len = min((u64)len - s, size);
@@ -1279,6 +1773,8 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
 		++ret;
 	}
 
+	if (ret == -EAGAIN)
+		vhost_iotlb_miss(vq, addr, access);
 	return ret;
 }
 
@@ -1313,7 +1809,7 @@ static int get_indirect(struct vhost_virtqueue *vq,
 	unsigned int i = 0, count, found = 0;
 	u32 len = vhost32_to_cpu(vq, indirect->len);
 	struct iov_iter from;
-	int ret;
+	int ret, access;
 
 	/* Sanity check */
 	if (unlikely(len % sizeof desc)) {
@@ -1325,9 +1821,10 @@ static int get_indirect(struct vhost_virtqueue *vq,
 	}
 
 	ret = translate_desc(vq, vhost64_to_cpu(vq, indirect->addr), len, vq->indirect,
-			     UIO_MAXIOV);
+			     UIO_MAXIOV, VHOST_ACCESS_RO);
 	if (unlikely(ret < 0)) {
-		vq_err(vq, "Translation failure %d in indirect.\n", ret);
+		if (ret != -EAGAIN)
+			vq_err(vq, "Translation failure %d in indirect.\n", ret);
 		return ret;
 	}
 	iov_iter_init(&from, READ, vq->indirect, ret, len);
@@ -1365,16 +1862,22 @@ static int get_indirect(struct vhost_virtqueue *vq,
 			return -EINVAL;
 		}
 
+		if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE))
+			access = VHOST_ACCESS_WO;
+		else
+			access = VHOST_ACCESS_RO;
+
 		ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
 				     vhost32_to_cpu(vq, desc.len), iov + iov_count,
-				     iov_size - iov_count);
+				     iov_size - iov_count, access);
 		if (unlikely(ret < 0)) {
-			vq_err(vq, "Translation failure %d indirect idx %d\n",
-			       ret, i);
+			if (ret != -EAGAIN)
+				vq_err(vq, "Translation failure %d indirect idx %d\n",
+					ret, i);
 			return ret;
 		}
 		/* If this is an input descriptor, increment that count. */
-		if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE)) {
+		if (access == VHOST_ACCESS_WO) {
 			*in_num += ret;
 			if (unlikely(log)) {
 				log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
@@ -1413,7 +1916,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 	u16 last_avail_idx;
 	__virtio16 avail_idx;
 	__virtio16 ring_head;
-	int ret;
+	int ret, access;
 
 	/* Check it isn't doing very strange things with descriptor numbers. */
 	last_avail_idx = vq->last_avail_idx;
@@ -1487,22 +1990,28 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 					   out_num, in_num,
 					   log, log_num, &desc);
 			if (unlikely(ret < 0)) {
-				vq_err(vq, "Failure detected "
-				       "in indirect descriptor at idx %d\n", i);
+				if (ret != -EAGAIN)
+					vq_err(vq, "Failure detected "
+						"in indirect descriptor at idx %d\n", i);
 				return ret;
 			}
 			continue;
 		}
 
+		if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE))
+			access = VHOST_ACCESS_WO;
+		else
+			access = VHOST_ACCESS_RO;
 		ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
 				     vhost32_to_cpu(vq, desc.len), iov + iov_count,
-				     iov_size - iov_count);
+				     iov_size - iov_count, access);
 		if (unlikely(ret < 0)) {
-			vq_err(vq, "Translation failure %d descriptor idx %d\n",
-			       ret, i);
+			if (ret != -EAGAIN)
+				vq_err(vq, "Translation failure %d descriptor idx %d\n",
+					ret, i);
 			return ret;
 		}
-		if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE)) {
+		if (access == VHOST_ACCESS_WO) {
 			/* If this is an input descriptor,
 			 * increment that count. */
 			*in_num += ret;
@@ -1768,6 +2277,47 @@ void vhost_disable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 }
 EXPORT_SYMBOL_GPL(vhost_disable_notify);
 
+/* Create a new message. */
+struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type)
+{
+	struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
+	if (!node)
+		return NULL;
+	node->vq = vq;
+	node->msg.type = type;
+	return node;
+}
+EXPORT_SYMBOL_GPL(vhost_new_msg);
+
+void vhost_enqueue_msg(struct vhost_dev *dev, struct list_head *head,
+		       struct vhost_msg_node *node)
+{
+	spin_lock(&dev->iotlb_lock);
+	list_add_tail(&node->node, head);
+	spin_unlock(&dev->iotlb_lock);
+
+	wake_up_interruptible_poll(&dev->wait, POLLIN | POLLRDNORM);
+}
+EXPORT_SYMBOL_GPL(vhost_enqueue_msg);
+
+struct vhost_msg_node *vhost_dequeue_msg(struct vhost_dev *dev,
+					 struct list_head *head)
+{
+	struct vhost_msg_node *node = NULL;
+
+	spin_lock(&dev->iotlb_lock);
+	if (!list_empty(head)) {
+		node = list_first_entry(head, struct vhost_msg_node,
+					node);
+		list_del(&node->node);
+	}
+	spin_unlock(&dev->iotlb_lock);
+
+	return node;
+}
+EXPORT_SYMBOL_GPL(vhost_dequeue_msg);
+
+
 static int __init vhost_init(void)
 {
 	return 0;