diff --git a/MAINTAINERS b/MAINTAINERS
index 8824115..980a69b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5619,6 +5619,15 @@ S:	Maintained
 F:	Documentation/filesystems/vfat.txt
 F:	fs/fat/
 
+VIRTIO HOST (VHOST)
+M:	"Michael S. Tsirkin" <mst@redhat.com>
+L:	kvm@vger.kernel.org
+L:	virtualization@lists.osdl.org
+L:	netdev@vger.kernel.org
+S:	Maintained
+F:	drivers/vhost/
+F:	include/linux/vhost.h
+
 VIA RHINE NETWORK DRIVER
 M:	Roger Luethi <rl@hellgate.ch>
 S:	Maintained
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index b84e571..94f44d9 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -64,6 +64,7 @@ config KVM_AMD
 
 # OK, it's a little counter-intuitive to do this, but it puts it neatly under
 # the virtualization menu.
+source drivers/vhost/Kconfig
 source drivers/lguest/Kconfig
 source drivers/virtio/Kconfig
 
diff --git a/drivers/Makefile b/drivers/Makefile
index 6ee53c7..81e3659 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -106,6 +106,7 @@ obj-$(CONFIG_HID)		+= hid/
 obj-$(CONFIG_PPC_PS3)		+= ps3/
 obj-$(CONFIG_OF)		+= of/
 obj-$(CONFIG_SSB)		+= ssb/
+obj-$(CONFIG_VHOST_NET)		+= vhost/
 obj-$(CONFIG_VIRTIO)		+= virtio/
 obj-$(CONFIG_VLYNQ)		+= vlynq/
 obj-$(CONFIG_STAGING)		+= staging/
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
new file mode 100644
index 0000000..9f409f4
--- /dev/null
+++ b/drivers/vhost/Kconfig
@@ -0,0 +1,11 @@
+config VHOST_NET
+	tristate "Host kernel accelerator for virtio net (EXPERIMENTAL)"
+	depends on NET && EVENTFD && EXPERIMENTAL
+	---help---
+	  This kernel module can be loaded in host kernel to accelerate
+	  guest networking with virtio_net. Not to be confused with virtio_net
+	  module itself which needs to be loaded in guest kernel.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called vhost_net.
+
diff --git a/drivers/vhost/Makefile b/drivers/vhost/Makefile
new file mode 100644
index 0000000..72dd020
--- /dev/null
+++ b/drivers/vhost/Makefile
@@ -0,0 +1,2 @@
+obj-$(CONFIG_VHOST_NET) += vhost_net.o
+vhost_net-y := vhost.o net.o
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
new file mode 100644
index 0000000..aeafaf3
--- /dev/null
+++ b/drivers/vhost/net.c
@@ -0,0 +1,633 @@
+/* Copyright (C) 2009 Red Hat, Inc.
+ * Author: Michael S. Tsirkin <mst@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ *
+ * virtio-net server in host kernel.
+ */
+
+#include <linux/compat.h>
+#include <linux/eventfd.h>
+#include <linux/vhost.h>
+#include <linux/virtio_net.h>
+#include <linux/mmu_context.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/workqueue.h>
+#include <linux/rcupdate.h>
+#include <linux/file.h>
+
+#include <linux/net.h>
+#include <linux/if_packet.h>
+#include <linux/if_arp.h>
+#include <linux/if_tun.h>
+
+#include <net/sock.h>
+
+#include "vhost.h"
+
+/* Max number of bytes transferred before requeueing the job.
+ * Using this limit prevents one virtqueue from starving others. */
+#define VHOST_NET_WEIGHT 0x80000
+
+enum {
+	VHOST_NET_VQ_RX = 0,
+	VHOST_NET_VQ_TX = 1,
+	VHOST_NET_VQ_MAX = 2,
+};
+
+enum vhost_net_poll_state {
+	VHOST_NET_POLL_DISABLED = 0,
+	VHOST_NET_POLL_STARTED = 1,
+	VHOST_NET_POLL_STOPPED = 2,
+};
+
+struct vhost_net {
+	struct vhost_dev dev;
+	struct vhost_virtqueue vqs[VHOST_NET_VQ_MAX];
+	struct vhost_poll poll[VHOST_NET_VQ_MAX];
+	/* Tells us whether we are polling a socket for TX.
+	 * We only do this when socket buffer fills up.
+	 * Protected by tx vq lock. */
+	enum vhost_net_poll_state tx_poll_state;
+};
+
+/* Pop first len bytes from iovec. Return number of segments used. */
+static int move_iovec_hdr(struct iovec *from, struct iovec *to,
+			  size_t len, int iov_count)
+{
+	int seg = 0;
+	size_t size;
+	while (len && seg < iov_count) {
+		size = min(from->iov_len, len);
+		to->iov_base = from->iov_base;
+		to->iov_len = size;
+		from->iov_len -= size;
+		from->iov_base += size;
+		len -= size;
+		++from;
+		++to;
+		++seg;
+	}
+	return seg;
+}
+
+/* Caller must have TX VQ lock */
+static void tx_poll_stop(struct vhost_net *net)
+{
+	if (likely(net->tx_poll_state != VHOST_NET_POLL_STARTED))
+		return;
+	vhost_poll_stop(net->poll + VHOST_NET_VQ_TX);
+	net->tx_poll_state = VHOST_NET_POLL_STOPPED;
+}
+
+/* Caller must have TX VQ lock */
+static void tx_poll_start(struct vhost_net *net, struct socket *sock)
+{
+	if (unlikely(net->tx_poll_state != VHOST_NET_POLL_STOPPED))
+		return;
+	vhost_poll_start(net->poll + VHOST_NET_VQ_TX, sock->file);
+	net->tx_poll_state = VHOST_NET_POLL_STARTED;
+}
+
+/* Expects to be always run from workqueue - which acts as
+ * read-size critical section for our kind of RCU. */
+static void handle_tx(struct vhost_net *net)
+{
+	struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
+	unsigned head, out, in, s;
+	struct msghdr msg = {
+		.msg_name = NULL,
+		.msg_namelen = 0,
+		.msg_control = NULL,
+		.msg_controllen = 0,
+		.msg_iov = vq->iov,
+		.msg_flags = MSG_DONTWAIT,
+	};
+	size_t len, total_len = 0;
+	int err, wmem;
+	size_t hdr_size;
+	struct socket *sock = rcu_dereference(vq->private_data);
+	if (!sock)
+		return;
+
+	wmem = atomic_read(&sock->sk->sk_wmem_alloc);
+	if (wmem >= sock->sk->sk_sndbuf)
+		return;
+
+	use_mm(net->dev.mm);
+	mutex_lock(&vq->mutex);
+	vhost_no_notify(vq);
+
+	if (wmem < sock->sk->sk_sndbuf * 2)
+		tx_poll_stop(net);
+	hdr_size = vq->hdr_size;
+
+	for (;;) {
+		head = vhost_get_vq_desc(&net->dev, vq, vq->iov, &out, &in,
+					 NULL, NULL);
+		/* Nothing new?  Wait for eventfd to tell us they refilled. */
+		if (head == vq->num) {
+			wmem = atomic_read(&sock->sk->sk_wmem_alloc);
+			if (wmem >= sock->sk->sk_sndbuf * 3 / 4) {
+				tx_poll_start(net, sock);
+				set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
+				break;
+			}
+			if (vhost_notify(vq))
+				continue;
+			break;
+		}
+		if (in) {
+			vq_err(vq, "Unexpected descriptor format for TX: "
+			       "out %d, int %d\n", out, in);
+			break;
+		}
+		/* Skip header. TODO: support TSO. */
+		s = move_iovec_hdr(vq->iov, vq->hdr, hdr_size, out);
+		msg.msg_iovlen = out;
+		len = iov_length(vq->iov, out);
+		/* Sanity check */
+		if (!len) {
+			vq_err(vq, "Unexpected header len for TX: "
+			       "%zd expected %zd\n",
+			       iov_length(vq->hdr, s), hdr_size);
+			break;
+		}
+		/* TODO: Check specific error and bomb out unless ENOBUFS? */
+		err = sock->ops->sendmsg(NULL, sock, &msg, len);
+		if (unlikely(err < 0)) {
+			vhost_discard_vq_desc(vq);
+			tx_poll_start(net, sock);
+			break;
+		}
+		if (err != len)
+			pr_err("Truncated TX packet: "
+			       " len %d != %zd\n", err, len);
+		vhost_add_used_and_trigger(&net->dev, vq, head, 0);
+		total_len += len;
+		if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
+			vhost_poll_queue(&vq->poll);
+			break;
+		}
+	}
+
+	mutex_unlock(&vq->mutex);
+	unuse_mm(net->dev.mm);
+}
+
+/* Expects to be always run from workqueue - which acts as
+ * read-size critical section for our kind of RCU. */
+static void handle_rx(struct vhost_net *net)
+{
+	struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_RX];
+	unsigned head, out, in, log, s;
+	struct vhost_log *vq_log;
+	struct msghdr msg = {
+		.msg_name = NULL,
+		.msg_namelen = 0,
+		.msg_control = NULL, /* FIXME: get and handle RX aux data. */
+		.msg_controllen = 0,
+		.msg_iov = vq->iov,
+		.msg_flags = MSG_DONTWAIT,
+	};
+
+	struct virtio_net_hdr hdr = {
+		.flags = 0,
+		.gso_type = VIRTIO_NET_HDR_GSO_NONE
+	};
+
+	size_t len, total_len = 0;
+	int err;
+	size_t hdr_size;
+	struct socket *sock = rcu_dereference(vq->private_data);
+	if (!sock || skb_queue_empty(&sock->sk->sk_receive_queue))
+		return;
+
+	use_mm(net->dev.mm);
+	mutex_lock(&vq->mutex);
+	vhost_no_notify(vq);
+	hdr_size = vq->hdr_size;
+
+	vq_log = unlikely(vhost_has_feature(&net->dev, VHOST_F_LOG_ALL)) ?
+		vq->log : NULL;
+
+	for (;;) {
+		head = vhost_get_vq_desc(&net->dev, vq, vq->iov, &out, &in,
+					 vq_log, &log);
+		/* OK, now we need to know about added descriptors. */
+		if (head == vq->num && vhost_notify(vq))
+			/* They could have slipped one in as we were doing that:
+			 * check again. */
+			continue;
+		/* Nothing new?  Wait for eventfd to tell us they refilled. */
+		if (head == vq->num)
+			break;
+		/* We don't need to be notified again. */
+		vhost_no_notify(vq);
+		if (out) {
+			vq_err(vq, "Unexpected descriptor format for RX: "
+			       "out %d, int %d\n",
+			       out, in);
+			break;
+		}
+		/* Skip header. TODO: support TSO/mergeable rx buffers. */
+		s = move_iovec_hdr(vq->iov, vq->hdr, hdr_size, in);
+		msg.msg_iovlen = in;
+		len = iov_length(vq->iov, in);
+		/* Sanity check */
+		if (!len) {
+			vq_err(vq, "Unexpected header len for RX: "
+			       "%zd expected %zd\n",
+			       iov_length(vq->hdr, s), hdr_size);
+			break;
+		}
+		err = sock->ops->recvmsg(NULL, sock, &msg,
+					 len, MSG_DONTWAIT | MSG_TRUNC);
+		/* TODO: Check specific error and bomb out unless EAGAIN? */
+		if (err < 0) {
+			vhost_discard_vq_desc(vq);
+			break;
+		}
+		/* TODO: Should check and handle checksum. */
+		if (err > len) {
+			pr_err("Discarded truncated rx packet: "
+			       " len %d > %zd\n", err, len);
+			vhost_discard_vq_desc(vq);
+			continue;
+		}
+		len = err;
+		err = memcpy_toiovec(vq->hdr, (unsigned char *)&hdr, hdr_size);
+		if (err) {
+			vq_err(vq, "Unable to write vnet_hdr at addr %p: %d\n",
+			       vq->iov->iov_base, err);
+			break;
+		}
+		len += hdr_size;
+		vhost_add_used_and_trigger(&net->dev, vq, head, len);
+		if (unlikely(vq_log))
+			vhost_log_write(vq, vq_log, log, len);
+		total_len += len;
+		if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
+			vhost_poll_queue(&vq->poll);
+			break;
+		}
+	}
+
+	mutex_unlock(&vq->mutex);
+	unuse_mm(net->dev.mm);
+}
+
+static void handle_tx_kick(struct work_struct *work)
+{
+	struct vhost_virtqueue *vq;
+	struct vhost_net *net;
+	vq = container_of(work, struct vhost_virtqueue, poll.work);
+	net = container_of(vq->dev, struct vhost_net, dev);
+	handle_tx(net);
+}
+
+static void handle_rx_kick(struct work_struct *work)
+{
+	struct vhost_virtqueue *vq;
+	struct vhost_net *net;
+	vq = container_of(work, struct vhost_virtqueue, poll.work);
+	net = container_of(vq->dev, struct vhost_net, dev);
+	handle_rx(net);
+}
+
+static void handle_tx_net(struct work_struct *work)
+{
+	struct vhost_net *net;
+	net = container_of(work, struct vhost_net, poll[VHOST_NET_VQ_TX].work);
+	handle_tx(net);
+}
+
+static void handle_rx_net(struct work_struct *work)
+{
+	struct vhost_net *net;
+	net = container_of(work, struct vhost_net, poll[VHOST_NET_VQ_RX].work);
+	handle_rx(net);
+}
+
+static int vhost_net_open(struct inode *inode, struct file *f)
+{
+	struct vhost_net *n = kzalloc(sizeof *n, GFP_KERNEL);
+	int r;
+	if (!n)
+		return -ENOMEM;
+	f->private_data = n;
+	n->vqs[VHOST_NET_VQ_TX].handle_kick = handle_tx_kick;
+	n->vqs[VHOST_NET_VQ_RX].handle_kick = handle_rx_kick;
+	r = vhost_dev_init(&n->dev, n->vqs, VHOST_NET_VQ_MAX);
+	if (r < 0) {
+		kfree(n);
+		return r;
+	}
+
+	vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT);
+	vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN);
+	n->tx_poll_state = VHOST_NET_POLL_DISABLED;
+	return 0;
+}
+
+static void vhost_net_disable_vq(struct vhost_net *n, int index)
+{
+	if (!n->vqs[index].private_data)
+		return;
+	if (index == VHOST_NET_VQ_TX) {
+		tx_poll_stop(n);
+		n->tx_poll_state = VHOST_NET_POLL_DISABLED;
+	} else
+		vhost_poll_stop(n->poll + VHOST_NET_VQ_RX);
+}
+
+static void vhost_net_enable_vq(struct vhost_net *n, int index)
+{
+	struct socket *sock = n->vqs[index].private_data;
+	if (!sock)
+		return;
+	if (index == VHOST_NET_VQ_TX) {
+		n->tx_poll_state = VHOST_NET_POLL_STOPPED;
+		tx_poll_start(n, sock);
+	} else
+		vhost_poll_start(n->poll + VHOST_NET_VQ_RX, sock->file);
+}
+
+static struct socket *vhost_net_stop_vq(struct vhost_net *n, int index)
+{
+	struct socket *sock;
+
+	mutex_lock(&n->vqs[index].mutex);
+	sock = n->vqs[index].private_data;
+	vhost_net_disable_vq(n, index);
+	rcu_assign_pointer(n->vqs[index].private_data, NULL);
+	mutex_unlock(&n->vqs[index].mutex);
+	return sock;
+}
+
+static void vhost_net_stop(struct vhost_net *n, struct socket **tx_sock,
+			   struct socket **rx_sock)
+{
+	*tx_sock = vhost_net_stop_vq(n, VHOST_NET_VQ_TX);
+	*rx_sock = vhost_net_stop_vq(n, VHOST_NET_VQ_RX);
+}
+
+static void vhost_net_flush_vq(struct vhost_net *n, int index)
+{
+	vhost_poll_flush(n->poll + index);
+	vhost_poll_flush(&n->dev.vqs[index].poll);
+}
+
+static void vhost_net_flush(struct vhost_net *n)
+{
+	vhost_net_flush_vq(n, VHOST_NET_VQ_TX);
+	vhost_net_flush_vq(n, VHOST_NET_VQ_RX);
+}
+
+static int vhost_net_release(struct inode *inode, struct file *f)
+{
+	struct vhost_net *n = f->private_data;
+	struct socket *tx_sock;
+	struct socket *rx_sock;
+
+	vhost_net_stop(n, &tx_sock, &rx_sock);
+	vhost_net_flush(n);
+	vhost_dev_cleanup(&n->dev);
+	if (tx_sock)
+		fput(tx_sock->file);
+	if (rx_sock)
+		fput(rx_sock->file);
+	/* We do an extra flush before freeing memory,
+	 * since jobs can re-queue themselves. */
+	vhost_net_flush(n);
+	kfree(n);
+	return 0;
+}
+
+static struct socket *get_raw_socket(int fd)
+{
+	struct {
+		struct sockaddr_ll sa;
+		char  buf[MAX_ADDR_LEN];
+	} uaddr;
+	int uaddr_len = sizeof uaddr, r;
+	struct socket *sock = sockfd_lookup(fd, &r);
+	if (!sock)
+		return ERR_PTR(-ENOTSOCK);
+
+	/* Parameter checking */
+	if (sock->sk->sk_type != SOCK_RAW) {
+		r = -ESOCKTNOSUPPORT;
+		goto err;
+	}
+
+	r = sock->ops->getname(sock, (struct sockaddr *)&uaddr.sa,
+			       &uaddr_len, 0);
+	if (r)
+		goto err;
+
+	if (uaddr.sa.sll_family != AF_PACKET) {
+		r = -EPFNOSUPPORT;
+		goto err;
+	}
+	return sock;
+err:
+	fput(sock->file);
+	return ERR_PTR(r);
+}
+
+static struct socket *get_tun_socket(int fd)
+{
+	struct file *file = fget(fd);
+	struct socket *sock;
+	if (!file)
+		return ERR_PTR(-EBADF);
+	sock = tun_get_socket(file);
+	if (IS_ERR(sock))
+		fput(file);
+	return sock;
+}
+
+static struct socket *get_socket(int fd)
+{
+	struct socket *sock;
+	if (fd == -1)
+		return NULL;
+	sock = get_raw_socket(fd);
+	if (!IS_ERR(sock))
+		return sock;
+	sock = get_tun_socket(fd);
+	if (!IS_ERR(sock))
+		return sock;
+	return ERR_PTR(-ENOTSOCK);
+}
+
+static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
+{
+	struct socket *sock, *oldsock = NULL;
+	struct vhost_virtqueue *vq;
+	int r;
+
+	mutex_lock(&n->dev.mutex);
+	r = vhost_dev_check_owner(&n->dev);
+	if (r)
+		goto done;
+
+	if (index >= VHOST_NET_VQ_MAX) {
+		r = -ENOBUFS;
+		goto done;
+	}
+	vq = n->vqs + index;
+	mutex_lock(&vq->mutex);
+	sock = get_socket(fd);
+	if (IS_ERR(sock)) {
+		r = PTR_ERR(sock);
+		goto done;
+	}
+
+	/* start polling new socket */
+	oldsock = vq->private_data;
+	if (sock == oldsock)
+		goto done;
+
+	vhost_net_disable_vq(n, index);
+	rcu_assign_pointer(vq->private_data, sock);
+	vhost_net_enable_vq(n, index);
+	mutex_unlock(&vq->mutex);
+done:
+	mutex_unlock(&n->dev.mutex);
+	if (oldsock) {
+		vhost_net_flush_vq(n, index);
+		fput(oldsock->file);
+	}
+	return r;
+}
+
+static long vhost_net_reset_owner(struct vhost_net *n)
+{
+	struct socket *tx_sock = NULL;
+	struct socket *rx_sock = NULL;
+	long r;
+	mutex_lock(&n->dev.mutex);
+	r = vhost_dev_check_owner(&n->dev);
+	if (r)
+		goto done;
+	vhost_net_stop(n, &tx_sock, &rx_sock);
+	vhost_net_flush(n);
+	r = vhost_dev_reset_owner(&n->dev);
+done:
+	mutex_unlock(&n->dev.mutex);
+	if (tx_sock)
+		fput(tx_sock->file);
+	if (rx_sock)
+		fput(rx_sock->file);
+	return r;
+}
+
+static void vhost_net_set_features(struct vhost_net *n, u64 features)
+{
+	size_t hdr_size = features & (1 << VHOST_NET_F_VIRTIO_NET_HDR) ?
+		sizeof(struct virtio_net_hdr) : 0;
+	int i;
+	mutex_lock(&n->dev.mutex);
+	n->dev.acked_features = features;
+	smp_wmb();
+	for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
+		mutex_lock(&n->vqs[i].mutex);
+		n->vqs[i].hdr_size = hdr_size;
+		mutex_unlock(&n->vqs[i].mutex);
+	}
+	mutex_unlock(&n->dev.mutex);
+	vhost_net_flush(n);
+}
+
+static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
+			    unsigned long arg)
+{
+	struct vhost_net *n = f->private_data;
+	void __user *argp = (void __user *)arg;
+	u32 __user *featurep = argp;
+	struct vhost_vring_file backend;
+	u64 features;
+	int r;
+	switch (ioctl) {
+	case VHOST_NET_SET_BACKEND:
+		r = copy_from_user(&backend, argp, sizeof backend);
+		if (r < 0)
+			return r;
+		return vhost_net_set_backend(n, backend.index, backend.fd);
+	case VHOST_GET_FEATURES:
+		features = VHOST_FEATURES;
+		return put_user(features, featurep);
+	case VHOST_ACK_FEATURES:
+		r = get_user(features, featurep);
+		/* No features for now */
+		if (r < 0)
+			return r;
+		if (features & ~VHOST_FEATURES)
+			return -EOPNOTSUPP;
+		vhost_net_set_features(n, features);
+		return 0;
+	case VHOST_RESET_OWNER:
+		return vhost_net_reset_owner(n);
+	default:
+		r = vhost_dev_ioctl(&n->dev, ioctl, arg);
+		vhost_net_flush(n);
+		return r;
+	}
+}
+
+#ifdef CONFIG_COMPAT
+static long vhost_net_compat_ioctl(struct file *f, unsigned int ioctl,
+				   unsigned long arg)
+{
+	return vhost_net_ioctl(f, ioctl, (unsigned long)compat_ptr(arg));
+}
+#endif
+
+const static struct file_operations vhost_net_fops = {
+	.owner          = THIS_MODULE,
+	.release        = vhost_net_release,
+	.unlocked_ioctl = vhost_net_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl   = vhost_net_compat_ioctl,
+#endif
+	.open           = vhost_net_open,
+};
+
+static struct miscdevice vhost_net_misc = {
+	VHOST_NET_MINOR,
+	"vhost-net",
+	&vhost_net_fops,
+};
+
+int vhost_net_init(void)
+{
+	int r = vhost_init();
+	if (r)
+		goto err_init;
+	r = misc_register(&vhost_net_misc);
+	if (r)
+		goto err_reg;
+	return 0;
+err_reg:
+	vhost_cleanup();
+err_init:
+	return r;
+
+}
+module_init(vhost_net_init);
+
+void vhost_net_exit(void)
+{
+	misc_deregister(&vhost_net_misc);
+	vhost_cleanup();
+}
+module_exit(vhost_net_exit);
+
+MODULE_VERSION("0.0.1");
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Michael S. Tsirkin");
+MODULE_DESCRIPTION("Host kernel accelerator for virtio net");
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
new file mode 100644
index 0000000..985f7f8
--- /dev/null
+++ b/drivers/vhost/vhost.c
@@ -0,0 +1,970 @@
+/* Copyright (C) 2009 Red Hat, Inc.
+ * Copyright (C) 2006 Rusty Russell IBM Corporation
+ *
+ * Author: Michael S. Tsirkin <mst@redhat.com>
+ *
+ * Inspiration, some code, and most witty comments come from
+ * Documentation/lguest/lguest.c, by Rusty Russell
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ *
+ * Generic code for virtio server in host kernel.
+ */
+
+#include <linux/eventfd.h>
+#include <linux/vhost.h>
+#include <linux/virtio_net.h>
+#include <linux/mm.h>
+#include <linux/miscdevice.h>
+#include <linux/mutex.h>
+#include <linux/workqueue.h>
+#include <linux/rcupdate.h>
+#include <linux/poll.h>
+#include <linux/file.h>
+#include <linux/highmem.h>
+
+#include <linux/net.h>
+#include <linux/if_packet.h>
+#include <linux/if_arp.h>
+
+#include <net/sock.h>
+
+#include "vhost.h"
+
+enum {
+	VHOST_MEMORY_MAX_NREGIONS = 64,
+	VHOST_MEMORY_F_LOG = 0x1,
+};
+
+static struct workqueue_struct *vhost_workqueue;
+
+static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
+			    poll_table *pt)
+{
+	struct vhost_poll *poll;
+	poll = container_of(pt, struct vhost_poll, table);
+
+	poll->wqh = wqh;
+	add_wait_queue(wqh, &poll->wait);
+}
+
+static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync,
+			     void *key)
+{
+	struct vhost_poll *poll;
+	poll = container_of(wait, struct vhost_poll, wait);
+	if (!((unsigned long)key & poll->mask))
+		return 0;
+
+	queue_work(vhost_workqueue, &poll->work);
+	return 0;
+}
+
+/* Init poll structure */
+void vhost_poll_init(struct vhost_poll *poll, work_func_t func,
+		     unsigned long mask)
+{
+	INIT_WORK(&poll->work, func);
+	init_waitqueue_func_entry(&poll->wait, vhost_poll_wakeup);
+	init_poll_funcptr(&poll->table, vhost_poll_func);
+	poll->mask = mask;
+}
+
+/* Start polling a file. We add ourselves to file's wait queue. The caller must
+ * keep a reference to a file until after vhost_poll_stop is called. */
+void vhost_poll_start(struct vhost_poll *poll, struct file *file)
+{
+	unsigned long mask;
+	mask = file->f_op->poll(file, &poll->table);
+	if (mask)
+		vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
+}
+
+/* Stop polling a file. After this function returns, it becomes safe to drop the
+ * file reference. You must also flush afterwards. */
+void vhost_poll_stop(struct vhost_poll *poll)
+{
+	remove_wait_queue(poll->wqh, &poll->wait);
+}
+
+/* Flush any work that has been scheduled. When calling this, don't hold any
+ * locks that are also used by the callback. */
+void vhost_poll_flush(struct vhost_poll *poll)
+{
+	flush_work(&poll->work);
+}
+
+void vhost_poll_queue(struct vhost_poll *poll)
+{
+	queue_work(vhost_workqueue, &poll->work);
+}
+
+long vhost_dev_init(struct vhost_dev *dev,
+		    struct vhost_virtqueue *vqs, int nvqs)
+{
+	int i;
+	dev->vqs = vqs;
+	dev->nvqs = nvqs;
+	mutex_init(&dev->mutex);
+
+	for (i = 0; i < dev->nvqs; ++i) {
+		dev->vqs[i].dev = dev;
+		mutex_init(&dev->vqs[i].mutex);
+		if (dev->vqs[i].handle_kick)
+			vhost_poll_init(&dev->vqs[i].poll,
+					dev->vqs[i].handle_kick,
+					POLLIN);
+	}
+	return 0;
+}
+
+/* Caller should have device mutex */
+long vhost_dev_check_owner(struct vhost_dev *dev)
+{
+	/* Are you the owner? If not, I don't think you mean to do that */
+	return dev->mm == current->mm ? 0 : -EPERM;
+}
+
+/* Caller should have device mutex */
+static long vhost_dev_set_owner(struct vhost_dev *dev)
+{
+	/* Is there an owner already? */
+	if (dev->mm)
+		return -EBUSY;
+	/* No owner, become one */
+	dev->mm = get_task_mm(current);
+	return 0;
+}
+
+/* Caller should have device mutex */
+long vhost_dev_reset_owner(struct vhost_dev *dev)
+{
+	struct vhost_memory *memory;
+
+	/* Restore memory to default 1:1 mapping. */
+	memory = kzalloc(offsetof(struct vhost_memory, regions) +
+			 2 * sizeof *memory->regions, GFP_KERNEL);
+	if (!memory)
+		return -ENOMEM;
+
+	vhost_dev_cleanup(dev);
+
+	memory->nregions = 2;
+	memory->regions[0].guest_phys_addr = 1;
+	memory->regions[0].userspace_addr = 1;
+	memory->regions[0].memory_size = ~0ULL;
+	memory->regions[1].guest_phys_addr = 0;
+	memory->regions[1].userspace_addr = 0;
+	memory->regions[1].memory_size = 1;
+	dev->memory = memory;
+	return 0;
+}
+
+/* Caller should have device mutex */
+void vhost_dev_cleanup(struct vhost_dev *dev)
+{
+	int i;
+	for (i = 0; i < dev->nvqs; ++i) {
+		if (dev->vqs[i].kick && dev->vqs[i].handle_kick) {
+			vhost_poll_stop(&dev->vqs[i].poll);
+			vhost_poll_flush(&dev->vqs[i].poll);
+		}
+		if (dev->vqs[i].error_ctx)
+			eventfd_ctx_put(dev->vqs[i].error_ctx);
+		if (dev->vqs[i].error)
+			fput(dev->vqs[i].error);
+		if (dev->vqs[i].kick)
+			fput(dev->vqs[i].kick);
+		if (dev->vqs[i].call_ctx)
+			eventfd_ctx_put(dev->vqs[i].call_ctx);
+		if (dev->vqs[i].call)
+			fput(dev->vqs[i].call);
+		dev->vqs[i].error_ctx = NULL;
+		dev->vqs[i].error = NULL;
+		dev->vqs[i].kick = NULL;
+		dev->vqs[i].call_ctx = NULL;
+		dev->vqs[i].call = NULL;
+	}
+	if (dev->log_ctx)
+		eventfd_ctx_put(dev->log_ctx);
+	dev->log_ctx = NULL;
+	if (dev->log_file)
+		fput(dev->log_file);
+	dev->log_file = NULL;
+	/* No one will access memory at this point */
+	kfree(dev->memory);
+	dev->memory = NULL;
+	if (dev->mm)
+		mmput(dev->mm);
+	dev->mm = NULL;
+}
+
+static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
+{
+	struct vhost_memory mem, *newmem, *oldmem;
+	unsigned long size = offsetof(struct vhost_memory, regions);
+	long r;
+	r = copy_from_user(&mem, m, size);
+	if (r)
+		return r;
+	if (mem.padding)
+		return -EOPNOTSUPP;
+	if (mem.nregions > VHOST_MEMORY_MAX_NREGIONS)
+		return -E2BIG;
+	newmem = kmalloc(size + mem.nregions * sizeof *m->regions, GFP_KERNEL);
+	if (!newmem)
+		return -ENOMEM;
+
+	memcpy(newmem, &mem, size);
+	r = copy_from_user(newmem->regions, m->regions,
+			   mem.nregions * sizeof *m->regions);
+	if (r) {
+		kfree(newmem);
+		return r;
+	}
+	oldmem = d->memory;
+	rcu_assign_pointer(d->memory, newmem);
+	synchronize_rcu();
+	kfree(oldmem);
+	return 0;
+}
+
+static int init_used(struct vhost_virtqueue *vq)
+{
+	int r = put_user(vq->used_flags, &vq->used->flags);
+	if (r)
+		return r;
+	return get_user(vq->last_used_idx, &vq->used->idx);
+}
+
+static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
+{
+	struct file *eventfp, *filep = NULL,
+		    *pollstart = NULL, *pollstop = NULL;
+	struct eventfd_ctx *ctx = NULL;
+	u32 __user *idxp = argp;
+	struct vhost_virtqueue *vq;
+	struct vhost_vring_state s;
+	struct vhost_vring_file f;
+	struct vhost_vring_addr a;
+	u32 idx;
+	long r;
+
+	r = get_user(idx, idxp);
+	if (r < 0)
+		return r;
+	if (idx > d->nvqs)
+		return -ENOBUFS;
+
+	vq = d->vqs + idx;
+
+	mutex_lock(&vq->mutex);
+
+	switch (ioctl) {
+	case VHOST_SET_VRING_NUM:
+		r = copy_from_user(&s, argp, sizeof s);
+		if (r < 0)
+			break;
+		if (s.num > 0xffff) {
+			r = -EINVAL;
+			break;
+		}
+		vq->num = s.num;
+		break;
+	case VHOST_SET_VRING_BASE:
+		r = copy_from_user(&s, argp, sizeof s);
+		if (r < 0)
+			break;
+		if (s.num > 0xffff) {
+			r = -EINVAL;
+			break;
+		}
+		vq->avail_idx = vq->last_avail_idx = s.num;
+		break;
+	case VHOST_GET_VRING_BASE:
+		s.index = idx;
+		s.num = vq->last_avail_idx;
+		r = copy_to_user(argp, &s, sizeof s);
+		break;
+	case VHOST_SET_VRING_DESC:
+		r = copy_from_user(&a, argp, sizeof a);
+		if (r < 0)
+			break;
+		if (a.padding) {
+			r = -EOPNOTSUPP;
+			break;
+		}
+		if ((u64)(unsigned long)a.user_addr != a.user_addr) {
+			r = -EFAULT;
+			break;
+		}
+		vq->desc = (void __user *)(unsigned long)a.user_addr;
+		break;
+	case VHOST_SET_VRING_AVAIL:
+		r = copy_from_user(&a, argp, sizeof a);
+		if (r < 0)
+			break;
+		if (a.padding) {
+			r = -EOPNOTSUPP;
+			break;
+		}
+		if ((u64)(unsigned long)a.user_addr != a.user_addr) {
+			r = -EFAULT;
+			break;
+		}
+		if (a.user_addr & (sizeof *vq->avail->ring - 1)) {
+			r = -EINVAL;
+			break;
+		}
+		vq->avail = (void __user *)(unsigned long)a.user_addr;
+		/* Forget the cached index value. */
+		vq->avail_idx = vq->last_avail_idx;
+		break;
+	case VHOST_SET_VRING_USED:
+		r = copy_from_user(&a, argp, sizeof a);
+		if (r < 0)
+			break;
+		if (a.padding) {
+			r = -EOPNOTSUPP;
+			break;
+		}
+		if ((u64)(unsigned long)a.user_addr != a.user_addr) {
+			r = -EFAULT;
+			break;
+		}
+		if (a.user_addr & (sizeof *vq->used->ring - 1)) {
+			r = -EINVAL;
+			break;
+		}
+		vq->used = (void __user *)(unsigned long)a.user_addr;
+		r = init_used(vq);
+		if (r)
+			break;
+		break;
+	case VHOST_SET_VRING_LOG:
+		r = copy_from_user(&a, argp, sizeof a);
+		if (r < 0)
+			break;
+		if (a.padding) {
+			r = -EOPNOTSUPP;
+			break;
+		}
+		if (a.user_addr == VHOST_VRING_LOG_DISABLE) {
+			vq->log_used = false;
+			break;
+		}
+		if (a.user_addr & (sizeof *vq->used->ring - 1)) {
+			r = -EINVAL;
+			break;
+		}
+		vq->log_used = true;
+		vq->log_addr = a.user_addr;
+		break;
+	case VHOST_SET_VRING_KICK:
+		r = copy_from_user(&f, argp, sizeof f);
+		if (r < 0)
+			break;
+		eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
+		if (IS_ERR(eventfp))
+			return PTR_ERR(eventfp);
+		if (eventfp != vq->kick) {
+			pollstop = filep = vq->kick;
+			pollstart = vq->kick = eventfp;
+		} else
+			filep = eventfp;
+		break;
+	case VHOST_SET_VRING_CALL:
+		r = copy_from_user(&f, argp, sizeof f);
+		if (r < 0)
+			break;
+		eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
+		if (IS_ERR(eventfp))
+			return PTR_ERR(eventfp);
+		if (eventfp != vq->call) {
+			filep = vq->call;
+			ctx = vq->call_ctx;
+			vq->call = eventfp;
+			vq->call_ctx = eventfp ?
+				eventfd_ctx_fileget(eventfp) : NULL;
+		} else
+			filep = eventfp;
+		break;
+	case VHOST_SET_VRING_ERR:
+		r = copy_from_user(&f, argp, sizeof f);
+		if (r < 0)
+			break;
+		eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
+		if (IS_ERR(eventfp))
+			return PTR_ERR(eventfp);
+		if (eventfp != vq->error) {
+			filep = vq->error;
+			vq->error = eventfp;
+			ctx = vq->error_ctx;
+			vq->error_ctx = eventfp ?
+				eventfd_ctx_fileget(eventfp) : NULL;
+		} else
+			filep = eventfp;
+		break;
+	default:
+		r = -ENOIOCTLCMD;
+	}
+
+	if (pollstop && vq->handle_kick)
+		vhost_poll_stop(&vq->poll);
+
+	if (ctx)
+		eventfd_ctx_put(ctx);
+	if (filep)
+		fput(filep);
+
+	if (pollstart && vq->handle_kick)
+		vhost_poll_start(&vq->poll, vq->kick);
+
+	mutex_unlock(&vq->mutex);
+
+	if (pollstop && vq->handle_kick)
+		vhost_poll_flush(&vq->poll);
+	return r;
+}
+
+long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, unsigned long arg)
+{
+	void __user *argp = (void __user *)arg;
+	struct file *eventfp, *filep = NULL;
+	struct eventfd_ctx *ctx = NULL;
+	u64 p;
+	long r;
+	int i, fd;
+
+	mutex_lock(&d->mutex);
+	/* If you are not the owner, you can become one */
+	if (ioctl == VHOST_SET_OWNER) {
+		r = vhost_dev_set_owner(d);
+		goto done;
+	}
+
+	/* You must be the owner to do anything else */
+	r = vhost_dev_check_owner(d);
+	if (r)
+		goto done;
+
+	switch (ioctl) {
+	case VHOST_SET_MEM_TABLE:
+		r = vhost_set_memory(d, argp);
+		break;
+	case VHOST_SET_LOG_BASE:
+		r = copy_from_user(&p, argp, sizeof p);
+		if (r < 0)
+			break;
+		if ((u64)(unsigned long)p != p) {
+			r = -EFAULT;
+			break;
+		}
+		for (i = 0; i < d->nvqs; ++i) {
+			mutex_lock(&d->vqs[i].mutex);
+			d->vqs[i].log_base = (void __user *)(unsigned long)p;
+			mutex_unlock(&d->vqs[i].mutex);
+		}
+		break;
+	case VHOST_SET_LOG_FD:
+		r = get_user(fd, (int __user *)argp);
+		if (r < 0)
+			break;
+		eventfp = fd == -1 ? NULL : eventfd_fget(fd);
+		if (IS_ERR(eventfp)) {
+			r = PTR_ERR(eventfp);
+			break;
+		}
+		if (eventfp != d->log_file) {
+			filep = d->log_file;
+			ctx = d->log_ctx;
+			d->log_ctx = eventfp ?
+				eventfd_ctx_fileget(eventfp) : NULL;
+		} else
+			filep = eventfp;
+		for (i = 0; i < d->nvqs; ++i) {
+			mutex_lock(&d->vqs[i].mutex);
+			d->vqs[i].log_ctx = d->log_ctx;
+			mutex_unlock(&d->vqs[i].mutex);
+		}
+		if (ctx)
+			eventfd_ctx_put(ctx);
+		if (filep)
+			fput(filep);
+		break;
+	default:
+		r = vhost_set_vring(d, ioctl, argp);
+		break;
+	}
+done:
+	mutex_unlock(&d->mutex);
+	return r;
+}
+
+static const struct vhost_memory_region *find_region(struct vhost_memory *mem,
+						     __u64 addr, __u32 len)
+{
+	struct vhost_memory_region *reg;
+	int i;
+	/* linear search is not brilliant, but we really have on the order of 6
+	 * regions in practice */
+	for (i = 0; i < mem->nregions; ++i) {
+		reg = mem->regions + i;
+		if (reg->guest_phys_addr <= addr &&
+		    reg->guest_phys_addr + reg->memory_size - 1 >= addr)
+			return reg;
+	}
+	return NULL;
+}
+
+/* TODO: This is really inefficient.  We need something like get_user()
+ * (instruction directly accesses the data, with an exception table entry
+ * returning -EFAULT). See Documentation/x86/exception-tables.txt.
+ */
+static int set_bit_to_user(int nr, void __user *addr)
+{
+	unsigned long log = (unsigned long)addr;
+	struct page *page;
+	void *base;
+	int bit = nr + (log % PAGE_SIZE) * 8;
+	int r;
+	r = get_user_pages_fast(log, 1, 1, &page);
+	if (r)
+		return r;
+	base = kmap_atomic(page, KM_USER0);
+	set_bit(bit, base);
+	kunmap_atomic(base, KM_USER0);
+	set_page_dirty_lock(page);
+	put_page(page);
+	return 0;
+}
+
+static int log_write(void __user *log_base,
+		     u64 write_address, u64 write_length)
+{
+	int r;
+	if (!write_length)
+		return 0;
+	write_address /= VHOST_PAGE_SIZE;
+	for (;;) {
+		u64 base = (u64)(unsigned long)log_base;
+		u64 log = base + write_address / 8;
+		int bit = write_address % 8;
+		if ((u64)(unsigned long)log != log)
+			return -EFAULT;
+		r = set_bit_to_user(bit, (void __user *)(unsigned long)log);
+		if (r < 0)
+			return r;
+		if (write_length <= VHOST_PAGE_SIZE)
+			break;
+		write_length -= VHOST_PAGE_SIZE;
+		write_address += VHOST_PAGE_SIZE;
+	}
+	return r;
+}
+
+int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
+		    unsigned int log_num, u64 len)
+{
+	int i, r;
+
+	/* Make sure data written is seen before log. */
+	wmb();
+	for (i = 0; i < log_num; ++i) {
+		u64 l = min(log[i].len, len);
+		r = log_write(vq->log_base, log[i].addr, l);
+		if (r < 0)
+			return r;
+		len -= l;
+		if (!len)
+			return 0;
+	}
+	if (vq->log_ctx)
+		eventfd_signal(vq->log_ctx, 1);
+	/* Length written exceeds what we have stored. This is a bug. */
+	BUG();
+	return 0;
+}
+
+int translate_desc(struct vhost_dev *dev, u64 addr, u32 len,
+		   struct iovec iov[], int iov_size)
+{
+	const struct vhost_memory_region *reg;
+	struct vhost_memory *mem;
+	struct iovec *_iov;
+	u64 s = 0;
+	int ret = 0;
+
+	rcu_read_lock();
+
+	mem = rcu_dereference(dev->memory);
+	while ((u64)len > s) {
+		u64 size;
+		if (ret >= iov_size) {
+			ret = -ENOBUFS;
+			break;
+		}
+		reg = find_region(mem, addr, len);
+		if (!reg) {
+			ret = -EFAULT;
+			break;
+		}
+		_iov = iov + ret;
+		size = reg->memory_size - addr + reg->guest_phys_addr;
+		_iov->iov_len = min((u64)len, size);
+		_iov->iov_base = (void *)(unsigned long)
+			(reg->userspace_addr + addr - reg->guest_phys_addr);
+		s += size;
+		addr += size;
+		++ret;
+	}
+
+	rcu_read_unlock();
+	return ret;
+}
+
+/* Each buffer in the virtqueues is actually a chain of descriptors.  This
+ * function returns the next descriptor in the chain,
+ * or -1 if we're at the end. */
+static unsigned next_desc(struct vring_desc *desc)
+{
+	unsigned int next;
+
+	/* If this descriptor says it doesn't chain, we're done. */
+	if (!(desc->flags & VRING_DESC_F_NEXT))
+		return -1;
+
+	/* Check they're not leading us off end of descriptors. */
+	next = desc->next;
+	/* Make sure compiler knows to grab that: we don't want it changing! */
+	/* We will use the result as an index in an array, so most
+	 * architectures only need a compiler barrier here. */
+	read_barrier_depends();
+
+	return next;
+}
+
+static unsigned get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
+			     struct iovec iov[],
+			     unsigned int *out_num, unsigned int *in_num,
+			     struct vhost_log *log, unsigned int *log_num,
+			     struct vring_desc *indirect)
+{
+	struct vring_desc desc;
+	unsigned int i = 0, count, found = 0;
+	int ret;
+
+	/* Sanity check */
+	if (indirect->len % sizeof desc) {
+		vq_err(vq, "Invalid length in indirect descriptor: "
+		       "len 0x%llx not multiple of 0x%zx\n",
+		       (unsigned long long)indirect->len,
+		       sizeof desc);
+		return -EINVAL;
+	}
+
+	ret = translate_desc(dev, indirect->addr, indirect->len, vq->indirect,
+			     ARRAY_SIZE(vq->indirect));
+	if (ret < 0) {
+		vq_err(vq, "Translation failure %d in indirect.\n", ret);
+		return ret;
+	}
+
+	/* We will use the result as an address to read from, so most
+	 * architectures only need a compiler barrier here. */
+	read_barrier_depends();
+
+	count = indirect->len / sizeof desc;
+	/* Buffers are chained via a 16 bit next field, so
+	 * we can have at most 2^16 of these. */
+	if (count > USHORT_MAX + 1) {
+		vq_err(vq, "Indirect buffer length too big: %d\n",
+		       indirect->len);
+		return -E2BIG;
+	}
+
+	do {
+		unsigned iov_count = *in_num + *out_num;
+		if (++found > count) {
+			vq_err(vq, "Loop detected: last one at %u "
+			       "indirect size %u\n",
+			       i, count);
+			return -EINVAL;
+		}
+		if (memcpy_fromiovec((unsigned char *)&desc, vq->indirect,
+				     sizeof desc)) {
+			vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n",
+			       i, (size_t)indirect->addr + i * sizeof desc);
+			return -EINVAL;
+		}
+		if (desc.flags & VRING_DESC_F_INDIRECT) {
+			vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n",
+			       i, (size_t)indirect->addr + i * sizeof desc);
+			return -EINVAL;
+		}
+
+		ret = translate_desc(dev, desc.addr, desc.len, iov + iov_count,
+				     VHOST_NET_MAX_SG - iov_count);
+		if (ret < 0) {
+			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 & VRING_DESC_F_WRITE) {
+			*in_num += ret;
+			if (unlikely(log)) {
+				log[*log_num].addr = desc.addr;
+				log[*log_num].len = desc.len;
+				++*log_num;
+			}
+		} else {
+			/* If it's an output descriptor, they're all supposed
+			 * to come before any input descriptors. */
+			if (*in_num) {
+				vq_err(vq, "Indirect descriptor "
+				       "has out after in: idx %d\n", i);
+				return -EINVAL;
+			}
+			*out_num += ret;
+		}
+	} while ((i = next_desc(&desc)) != -1);
+	return 0;
+}
+
+/* This looks in the virtqueue and for the first available buffer, and converts
+ * it to an iovec for convenient access.  Since descriptors consist of some
+ * number of output then some number of input descriptors, it's actually two
+ * iovecs, but we pack them into one and note how many of each there were.
+ *
+ * This function returns the descriptor number found, or vq->num (which
+ * is never a valid descriptor number) if none was found. */
+unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
+			   struct iovec iov[],
+			   unsigned int *out_num, unsigned int *in_num,
+			   struct vhost_log *log, unsigned int *log_num)
+{
+	struct vring_desc desc;
+	unsigned int i, head, found = 0;
+	u16 last_avail_idx;
+	int ret;
+
+	/* Check it isn't doing very strange things with descriptor numbers. */
+	last_avail_idx = vq->last_avail_idx;
+	if (get_user(vq->avail_idx, &vq->avail->idx)) {
+		vq_err(vq, "Failed to access avail idx at %p\n",
+		       &vq->avail->idx);
+		return vq->num;
+	}
+
+	if ((u16)(vq->avail_idx - last_avail_idx) > vq->num) {
+		vq_err(vq, "Guest moved used index from %u to %u",
+		       last_avail_idx, vq->avail_idx);
+		return vq->num;
+	}
+
+	/* If there's nothing new since last we looked, return invalid. */
+	if (vq->avail_idx == last_avail_idx)
+		return vq->num;
+
+	/* Only get avail ring entries after they have been exposed by guest. */
+	rmb();
+
+	/* Grab the next descriptor number they're advertising, and increment
+	 * the index we've seen. */
+	if (get_user(head, &vq->avail->ring[last_avail_idx % vq->num])) {
+		vq_err(vq, "Failed to read head: idx %d address %p\n",
+		       last_avail_idx,
+		       &vq->avail->ring[last_avail_idx % vq->num]);
+		return vq->num;
+	}
+
+	/* If their number is silly, that's an error. */
+	if (head >= vq->num) {
+		vq_err(vq, "Guest says index %u > %u is available",
+		       head, vq->num);
+		return vq->num;
+	}
+
+	/* When we start there are none of either input nor output. */
+	*out_num = *in_num = 0;
+	if (unlikely(log))
+		*log_num = 0;
+
+	i = head;
+	do {
+		unsigned iov_count = *in_num + *out_num;
+		if (i >= vq->num) {
+			vq_err(vq, "Desc index is %u > %u, head = %u",
+			       i, vq->num, head);
+			return vq->num;
+		}
+		if (++found > vq->num) {
+			vq_err(vq, "Loop detected: last one at %u "
+			       "vq size %u head %u\n",
+			       i, vq->num, head);
+			return vq->num;
+		}
+		ret = copy_from_user(&desc, vq->desc + i, sizeof desc);
+		if (ret) {
+			vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
+			       i, vq->desc + i);
+			return vq->num;
+		}
+		if (desc.flags & VRING_DESC_F_INDIRECT) {
+			ret = get_indirect(dev, vq, iov, out_num, in_num,
+					   log, log_num, &desc);
+			if (ret < 0) {
+				vq_err(vq, "Failure detected "
+				       "in indirect descriptor at idx %d\n", i);
+				return vq->num;
+			}
+			continue;
+		}
+
+		ret = translate_desc(dev, desc.addr, desc.len, iov + iov_count,
+				     VHOST_NET_MAX_SG - iov_count);
+		if (ret < 0) {
+			vq_err(vq, "Translation failure %d descriptor idx %d\n",
+			       ret, i);
+			return vq->num;
+		}
+		if (desc.flags & VRING_DESC_F_WRITE) {
+			/* If this is an input descriptor,
+			 * increment that count. */
+			*in_num += ret;
+			if (unlikely(log)) {
+				log[*log_num].addr = desc.addr;
+				log[*log_num].len = desc.len;
+				++*log_num;
+			}
+		} else {
+			/* If it's an output descriptor, they're all supposed
+			 * to come before any input descriptors. */
+			if (*in_num) {
+				vq_err(vq, "Descriptor has out after in: "
+				       "idx %d\n", i);
+				return vq->num;
+			}
+			*out_num += ret;
+		}
+	} while ((i = next_desc(&desc)) != -1);
+
+	/* On success, increment avail index. */
+	vq->last_avail_idx++;
+	return head;
+}
+
+/* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
+void vhost_discard_vq_desc(struct vhost_virtqueue *vq)
+{
+	vq->last_avail_idx--;
+}
+
+/* After we've used one of their buffers, we tell them about it.  We'll then
+ * want to send them an interrupt, using vq->call. */
+int vhost_add_used(struct vhost_virtqueue *vq,
+			  unsigned int head, int len)
+{
+	struct vring_used_elem *used;
+
+	/* The virtqueue contains a ring of used buffers.  Get a pointer to the
+	 * next entry in that used ring. */
+	used = &vq->used->ring[vq->last_used_idx % vq->num];
+	if (put_user(head, &used->id)) {
+		vq_err(vq, "Failed to write used id");
+		return -EFAULT;
+	}
+	if (put_user(len, &used->len)) {
+		vq_err(vq, "Failed to write used len");
+		return -EFAULT;
+	}
+	/* Make sure buffer is written before we update index. */
+	wmb();
+	if (put_user(vq->last_used_idx + 1, &vq->used->idx)) {
+		vq_err(vq, "Failed to increment used idx");
+		return -EFAULT;
+	}
+	if (unlikely(vq->log_used)) {
+		/* Make sure data is seen before log. */
+		wmb();
+		log_write(vq->log_base, vq->log_addr + sizeof *vq->used->ring *
+			  (vq->last_used_idx % vq->num),
+			  sizeof *vq->used->ring);
+		log_write(vq->log_base, vq->log_addr, sizeof *vq->used->ring);
+		if (vq->log_ctx)
+			eventfd_signal(vq->log_ctx, 1);
+	}
+	vq->last_used_idx++;
+	return 0;
+}
+
+/* This actually sends the interrupt for this virtqueue */
+void vhost_trigger_irq(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+{
+	__u16 flags = 0;
+	if (get_user(flags, &vq->avail->flags)) {
+		vq_err(vq, "Failed to get flags");
+		return;
+	}
+
+	/* If they don't want an interrupt, don't send one, unless empty. */
+	if ((flags & VRING_AVAIL_F_NO_INTERRUPT) &&
+	    (vq->avail_idx != vq->last_avail_idx ||
+	     !vhost_has_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY)))
+		return;
+
+	/* Send the Guest an interrupt tell them we used something up. */
+	if (vq->call_ctx)
+		eventfd_signal(vq->call_ctx, 1);
+}
+
+/* And here's the combo meal deal.  Supersize me! */
+void vhost_add_used_and_trigger(struct vhost_dev *dev,
+				struct vhost_virtqueue *vq,
+				unsigned int head, int len)
+{
+	vhost_add_used(vq, head, len);
+	vhost_trigger_irq(dev, vq);
+}
+
+/* OK, now we need to know about added descriptors. */
+bool vhost_notify(struct vhost_virtqueue *vq)
+{
+	int r;
+	if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
+		return false;
+	vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;
+	r = put_user(vq->used_flags, &vq->used->flags);
+	if (r)
+		vq_err(vq, "Failed to disable notification: %d\n", r);
+	/* They could have slipped one in as we were doing that: make
+	 * sure it's written, tell caller it needs to check again. */
+	mb();
+	return true;
+}
+
+/* We don't need to be notified again. */
+void vhost_no_notify(struct vhost_virtqueue *vq)
+{
+	int r;
+	if (vq->used_flags & VRING_USED_F_NO_NOTIFY)
+		return;
+	vq->used_flags |= VRING_USED_F_NO_NOTIFY;
+	r = put_user(vq->used_flags, &vq->used->flags);
+	if (r)
+		vq_err(vq, "Failed to enable notification: %d\n", r);
+}
+
+int vhost_init(void)
+{
+	vhost_workqueue = create_singlethread_workqueue("vhost");
+	if (!vhost_workqueue)
+		return -ENOMEM;
+	return 0;
+}
+
+void vhost_cleanup(void)
+{
+	destroy_workqueue(vhost_workqueue);
+}
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
new file mode 100644
index 0000000..d3900de
--- /dev/null
+++ b/drivers/vhost/vhost.h
@@ -0,0 +1,158 @@
+#ifndef _VHOST_H
+#define _VHOST_H
+
+#include <linux/eventfd.h>
+#include <linux/vhost.h>
+#include <linux/mm.h>
+#include <linux/mutex.h>
+#include <linux/workqueue.h>
+#include <linux/poll.h>
+#include <linux/file.h>
+#include <linux/skbuff.h>
+#include <linux/uio.h>
+#include <linux/virtio_config.h>
+#include <linux/virtio_ring.h>
+
+struct vhost_device;
+
+enum {
+	VHOST_NET_MAX_SG = MAX_SKB_FRAGS + 2,
+};
+
+/* Poll a file (eventfd or socket) */
+/* Note: there's nothing vhost specific about this structure. */
+struct vhost_poll {
+	poll_table                table;
+	wait_queue_head_t        *wqh;
+	wait_queue_t              wait;
+	/* struct which will handle all actual work. */
+	struct work_struct        work;
+	unsigned long		  mask;
+};
+
+void vhost_poll_init(struct vhost_poll *poll, work_func_t func,
+		     unsigned long mask);
+void vhost_poll_start(struct vhost_poll *poll, struct file *file);
+void vhost_poll_stop(struct vhost_poll *poll);
+void vhost_poll_flush(struct vhost_poll *poll);
+void vhost_poll_queue(struct vhost_poll *poll);
+
+struct vhost_log {
+	u64 addr;
+	u64 len;
+};
+
+/* The virtqueue structure describes a queue attached to a device. */
+struct vhost_virtqueue {
+	struct vhost_dev *dev;
+
+	/* The actual ring of buffers. */
+	struct mutex mutex;
+	unsigned int num;
+	struct vring_desc __user *desc;
+	struct vring_avail __user *avail;
+	struct vring_used __user *used;
+	struct file *kick;
+	struct file *call;
+	struct file *error;
+	struct eventfd_ctx *call_ctx;
+	struct eventfd_ctx *error_ctx;
+	struct eventfd_ctx *log_ctx;
+
+	struct vhost_poll poll;
+
+	/* The routine to call when the Guest pings us, or timeout. */
+	work_func_t handle_kick;
+
+	/* Last available index we saw. */
+	u16 last_avail_idx;
+
+	/* Caches available index value from user. */
+	u16 avail_idx;
+
+	/* Last index we used. */
+	u16 last_used_idx;
+
+	/* Used flags */
+	u16 used_flags;
+
+	/* Log writes to used structure. */
+	bool log_used;
+	u64 log_addr;
+
+	struct iovec indirect[VHOST_NET_MAX_SG];
+	struct iovec iov[VHOST_NET_MAX_SG];
+	struct iovec hdr[VHOST_NET_MAX_SG];
+	size_t hdr_size;
+	/* We use a kind of RCU to access private pointer.
+	 * All readers access it from workqueue, which makes it possible to
+	 * flush the workqueue instead of synchronize_rcu. Therefore readers do
+	 * not need to call rcu_read_lock/rcu_read_unlock: the beginning of
+	 * work item execution acts instead of rcu_read_lock() and the end of
+	 * work item execution acts instead of rcu_read_lock().
+	 * Writers use virtqueue mutex. */
+	void *private_data;
+	/* Log write descriptors */
+	void __user *log_base;
+	struct vhost_log log[VHOST_NET_MAX_SG];
+};
+
+struct vhost_dev {
+	/* Readers use RCU to access memory table pointer
+	 * log base pointer and features.
+	 * Writers use mutex below.*/
+	struct vhost_memory *memory;
+	struct mm_struct *mm;
+	struct mutex mutex;
+	unsigned acked_features;
+	struct vhost_virtqueue *vqs;
+	int nvqs;
+	struct file *log_file;
+	struct eventfd_ctx *log_ctx;
+};
+
+long vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue *vqs, int nvqs);
+long vhost_dev_check_owner(struct vhost_dev *);
+long vhost_dev_reset_owner(struct vhost_dev *);
+void vhost_dev_cleanup(struct vhost_dev *);
+long vhost_dev_ioctl(struct vhost_dev *, unsigned int ioctl, unsigned long arg);
+
+unsigned vhost_get_vq_desc(struct vhost_dev *, struct vhost_virtqueue *,
+			   struct iovec iov[],
+			   unsigned int *out_num, unsigned int *in_num,
+			   struct vhost_log *log, unsigned int *log_num);
+void vhost_discard_vq_desc(struct vhost_virtqueue *);
+
+int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
+void vhost_trigger_irq(struct vhost_dev *, struct vhost_virtqueue *);
+void vhost_add_used_and_trigger(struct vhost_dev *, struct vhost_virtqueue *,
+				unsigned int head, int len);
+void vhost_no_notify(struct vhost_virtqueue *);
+bool vhost_notify(struct vhost_virtqueue *);
+
+int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
+		    unsigned int log_num, u64 len);
+
+int vhost_init(void);
+void vhost_cleanup(void);
+
+#define vq_err(vq, fmt, ...) do {                                  \
+		pr_debug(pr_fmt(fmt), ##__VA_ARGS__);       \
+		if ((vq)->error_ctx)                               \
+				eventfd_signal((vq)->error_ctx, 1);\
+	} while (0)
+
+enum {
+	VHOST_FEATURES = (1 << VIRTIO_F_NOTIFY_ON_EMPTY) |
+			 (1 << VIRTIO_RING_F_INDIRECT_DESC) |
+			 (1 << VHOST_F_LOG_ALL) |
+			 (1 << VHOST_NET_F_VIRTIO_NET_HDR),
+};
+
+static inline int vhost_has_feature(struct vhost_dev *dev, int bit)
+{
+	unsigned acked_features = rcu_dereference(dev->acked_features);
+	return acked_features & (1 << bit);
+}
+
+#endif
diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index 3f384d4..b6335c6 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -361,6 +361,7 @@ unifdef-y += uio.h
 unifdef-y += unistd.h
 unifdef-y += usbdevice_fs.h
 unifdef-y += utsname.h
+unifdef-y += vhost.h
 unifdef-y += videodev2.h
 unifdef-y += videodev.h
 unifdef-y += virtio_config.h
diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h
index adaf3c1..8b5f7cc 100644
--- a/include/linux/miscdevice.h
+++ b/include/linux/miscdevice.h
@@ -30,6 +30,7 @@
 #define HPET_MINOR		228
 #define FUSE_MINOR		229
 #define KVM_MINOR		232
+#define VHOST_NET_MINOR		233
 #define MISC_DYNAMIC_MINOR	255
 
 struct device;
diff --git a/include/linux/vhost.h b/include/linux/vhost.h
new file mode 100644
index 0000000..f66142f
--- /dev/null
+++ b/include/linux/vhost.h
@@ -0,0 +1,126 @@
+#ifndef _LINUX_VHOST_H
+#define _LINUX_VHOST_H
+/* Userspace interface for in-kernel virtio accelerators. */
+
+/* vhost is used to reduce the number of system calls involved in virtio.
+ *
+ * Existing virtio net code is used in the guest without modification.
+ *
+ * This header includes interface used by userspace hypervisor for
+ * device configuration.
+ */
+
+#include <linux/types.h>
+#include <linux/compiler.h>
+#include <linux/ioctl.h>
+#include <linux/virtio_config.h>
+#include <linux/virtio_ring.h>
+
+struct vhost_vring_state {
+	unsigned int index;
+	unsigned int num;
+};
+
+struct vhost_vring_file {
+	unsigned int index;
+	int fd; /* Pass -1 to unbind from file. */
+
+};
+
+struct vhost_vring_addr {
+	unsigned int index;
+	unsigned int padding;
+	__u64 user_addr;
+};
+
+struct vhost_memory_region {
+	__u64 guest_phys_addr;
+	__u64 memory_size; /* bytes */
+	__u64 userspace_addr;
+	__u64 flags_padding; /* No flags are currently specified. */
+};
+
+/* All region addresses and sizes must be 4K aligned. */
+#define VHOST_PAGE_SIZE 0x1000
+
+struct vhost_memory {
+	__u32 nregions;
+	__u32 padding;
+	struct vhost_memory_region regions[0];
+};
+
+/* ioctls */
+
+#define VHOST_VIRTIO 0xAF
+
+/* Features bitmask for forward compatibility.  Transport bits are used for
+ * vhost specific features. */
+#define VHOST_GET_FEATURES	_IOR(VHOST_VIRTIO, 0x00, __u64)
+#define VHOST_ACK_FEATURES	_IOW(VHOST_VIRTIO, 0x00, __u64)
+
+/* Set current process as the (exclusive) owner of this file descriptor.  This
+ * must be called before any other vhost command.  Further calls to
+ * VHOST_OWNER_SET fail until VHOST_OWNER_RESET is called. */
+#define VHOST_SET_OWNER _IO(VHOST_VIRTIO, 0x01)
+/* Give up ownership, and reset the device to default values.
+ * Allows subsequent call to VHOST_OWNER_SET to succeed. */
+#define VHOST_RESET_OWNER _IO(VHOST_VIRTIO, 0x02)
+
+/* Set up/modify memory layout */
+#define VHOST_SET_MEM_TABLE	_IOW(VHOST_VIRTIO, 0x03, struct vhost_memory)
+
+/* Write logging setup. */
+/* Memory writes can optionally be logged by setting bit at an offset
+ * (calculated from the physical address) from specified log base.
+ * The bit is set using an atomic 32 bit operation. */
+/* Set base address for logging. */
+#define VHOST_SET_LOG_BASE _IOW(VHOST_VIRTIO, 0x04, __u64)
+/* Specify an eventfd file descriptor to signal on log write. */
+#define VHOST_SET_LOG_FD _IOW(VHOST_VIRTIO, 0x07, int)
+
+/* Ring setup. These parameters can not be modified while ring is running
+ * (bound to a device). */
+/* Set number of descriptors in ring */
+#define VHOST_SET_VRING_NUM _IOW(VHOST_VIRTIO, 0x10, struct vhost_vring_state)
+/* Start of array of descriptors (virtually contiguous) */
+#define VHOST_SET_VRING_DESC _IOW(VHOST_VIRTIO, 0x11, struct vhost_vring_addr)
+/* Used structure address. Must be 32 bit aligned */
+#define VHOST_SET_VRING_USED _IOW(VHOST_VIRTIO, 0x12, struct vhost_vring_addr)
+/* Available structure address. Must be 16 bit aligned */
+#define VHOST_SET_VRING_AVAIL _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_addr)
+/* Base value where queue looks for available descriptors */
+#define VHOST_SET_VRING_BASE _IOW(VHOST_VIRTIO, 0x14, struct vhost_vring_state)
+/* Get accessor: reads index, writes value in num */
+#define VHOST_GET_VRING_BASE _IOWR(VHOST_VIRTIO, 0x14, struct vhost_vring_state)
+
+/* Logging support. Can be modified while ring is running. */
+/* Log writes to used structure, at offset calculated from specified address.
+ * Address must be 32 bit aligned. Pass 0x1 to disable logging. */
+#define VHOST_SET_VRING_LOG _IOW(VHOST_VIRTIO, 0x18, struct vhost_vring_addr)
+#define VHOST_VRING_LOG_DISABLE (0x1)
+
+/* The following ioctls use eventfd file descriptors to signal and poll
+ * for events. */
+
+/* Set eventfd to poll for added buffers */
+#define VHOST_SET_VRING_KICK _IOW(VHOST_VIRTIO, 0x20, struct vhost_vring_file)
+/* Set eventfd to signal when buffers have beed used */
+#define VHOST_SET_VRING_CALL _IOW(VHOST_VIRTIO, 0x21, struct vhost_vring_file)
+/* Set eventfd to signal an error */
+#define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file)
+
+/* VHOST_NET specific defines */
+
+/* Attach virtio net ring to a raw socket, or tap device.
+ * The socket must be already bound to an ethernet device, this device will be
+ * used for transmit.  Pass fd -1 to unbind from the socket and the transmit
+ * device.  This can be used to stop the ring (e.g. for migration). */
+#define VHOST_NET_SET_BACKEND _IOW(VHOST_VIRTIO, 0x30, struct vhost_vring_file)
+
+/* Feature bits */
+/* Log all write descriptors. Can be changed while device is active. */
+#define VHOST_F_LOG_ALL 26
+/* vhost-net should add virtio_net_hdr for RX, and strip for TX packets. */
+#define VHOST_NET_F_VIRTIO_NET_HDR 27
+
+#endif
