[PATCHv4 1/2] mm: export use_mm/unuse_mm to modules

[PATCHv4 1/2] mm: export use_mm/unuse_mm to modules

[Michael S. Tsirkin]

vhost net module wants to do copy to/from user from a kernel thread,
which needs use_mm (like what fs/aio has).  Move that into mm/ and
export to modules.

Acked-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

---
 fs/aio.c                    |   47 +----------------------------------
 include/linux/mmu_context.h |    9 ++++++
 mm/Makefile                 |    2 +-
 mm/mmu_context.c            |   58 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 69 insertions(+), 47 deletions(-)
 create mode 100644 include/linux/mmu_context.h
 create mode 100644 mm/mmu_context.c

diff --git a/fs/aio.c b/fs/aio.c
index d065b2c..fc21c23 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -24,6 +24,7 @@
 #include <linux/file.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
+#include <linux/mmu_context.h>
 #include <linux/slab.h>
 #include <linux/timer.h>
 #include <linux/aio.h>
@@ -34,7 +35,6 @@
 
 #include <asm/kmap_types.h>
 #include <asm/uaccess.h>
-#include <asm/mmu_context.h>
 
 #if DEBUG > 1
 #define dprintk		printk
@@ -595,51 +595,6 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
 }
 
 /*
- * use_mm
- *	Makes the calling kernel thread take on the specified
- *	mm context.
- *	Called by the retry thread execute retries within the
- *	iocb issuer's mm context, so that copy_from/to_user
- *	operations work seamlessly for aio.
- *	(Note: this routine is intended to be called only
- *	from a kernel thread context)
- */
-static void use_mm(struct mm_struct *mm)
-{
-	struct mm_struct *active_mm;
-	struct task_struct *tsk = current;
-
-	task_lock(tsk);
-	active_mm = tsk->active_mm;
-	atomic_inc(&mm->mm_count);
-	tsk->mm = mm;
-	tsk->active_mm = mm;
-	switch_mm(active_mm, mm, tsk);
-	task_unlock(tsk);
-
-	mmdrop(active_mm);
-}
-
-/*
- * unuse_mm
- *	Reverses the effect of use_mm, i.e. releases the
- *	specified mm context which was earlier taken on
- *	by the calling kernel thread
- *	(Note: this routine is intended to be called only
- *	from a kernel thread context)
- */
-static void unuse_mm(struct mm_struct *mm)
-{
-	struct task_struct *tsk = current;
-
-	task_lock(tsk);
-	tsk->mm = NULL;
-	/* active_mm is still 'mm' */
-	enter_lazy_tlb(mm, tsk);
-	task_unlock(tsk);
-}
-
-/*
  * Queue up a kiocb to be retried. Assumes that the kiocb
  * has already been marked as kicked, and places it on
  * the retry run list for the corresponding ioctx, if it
diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
new file mode 100644
index 0000000..70fffeb
--- /dev/null
+++ b/include/linux/mmu_context.h
@@ -0,0 +1,9 @@
+#ifndef _LINUX_MMU_CONTEXT_H
+#define _LINUX_MMU_CONTEXT_H
+
+struct mm_struct;
+
+void use_mm(struct mm_struct *mm);
+void unuse_mm(struct mm_struct *mm);
+
+#endif
diff --git a/mm/Makefile b/mm/Makefile
index 5e0bd64..46c3892 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -11,7 +11,7 @@ obj-y			:= bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
 			   maccess.o page_alloc.o page-writeback.o pdflush.o \
 			   readahead.o swap.o truncate.o vmscan.o shmem.o \
 			   prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
-			   page_isolation.o mm_init.o $(mmu-y)
+			   page_isolation.o mm_init.o mmu_context.o $(mmu-y)
 obj-y += init-mm.o
 
 obj-$(CONFIG_PROC_PAGE_MONITOR) += pagewalk.o
diff --git a/mm/mmu_context.c b/mm/mmu_context.c
new file mode 100644
index 0000000..9989c2f
--- /dev/null
+++ b/mm/mmu_context.c
@@ -0,0 +1,58 @@
+/* Copyright (C) 2009 Red Hat, Inc.
+ *
+ * See ../COPYING for licensing terms.
+ */
+
+#include <linux/mm.h>
+#include <linux/mmu_context.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+
+#include <asm/mmu_context.h>
+
+/*
+ * use_mm
+ *	Makes the calling kernel thread take on the specified
+ *	mm context.
+ *	Called by the retry thread execute retries within the
+ *	iocb issuer's mm context, so that copy_from/to_user
+ *	operations work seamlessly for aio.
+ *	(Note: this routine is intended to be called only
+ *	from a kernel thread context)
+ */
+void use_mm(struct mm_struct *mm)
+{
+	struct mm_struct *active_mm;
+	struct task_struct *tsk = current;
+
+	task_lock(tsk);
+	active_mm = tsk->active_mm;
+	atomic_inc(&mm->mm_count);
+	tsk->mm = mm;
+	tsk->active_mm = mm;
+	switch_mm(active_mm, mm, tsk);
+	task_unlock(tsk);
+
+	mmdrop(active_mm);
+}
+EXPORT_SYMBOL_GPL(use_mm);
+
+/*
+ * unuse_mm
+ *	Reverses the effect of use_mm, i.e. releases the
+ *	specified mm context which was earlier taken on
+ *	by the calling kernel thread
+ *	(Note: this routine is intended to be called only
+ *	from a kernel thread context)
+ */
+void unuse_mm(struct mm_struct *mm)
+{
+	struct task_struct *tsk = current;
+
+	task_lock(tsk);
+	tsk->mm = NULL;
+	/* active_mm is still 'mm' */
+	enter_lazy_tlb(mm, tsk);
+	task_unlock(tsk);
+}
+EXPORT_SYMBOL_GPL(unuse_mm);
-- 
1.6.2.5

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[PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Michael S. Tsirkin]

What it is: vhost net is a character device that can be used to reduce
the number of system calls involved in virtio networking.
Existing virtio net code is used in the guest without modification.

There's similarity with vringfd, with some differences and reduced scope
- uses eventfd for signalling
- structures can be moved around in memory at any time (good for migration)
- support memory table and not just an offset (needed for kvm)

common virtio related code has been put in a separate file vhost.c and
can be made into a separate module if/when more backends appear.  I used
Rusty's lguest.c as the source for developing this part : this supplied
me with witty comments I wouldn't be able to write myself.

What it is not: vhost net is not a bus, and not a generic new system
call. No assumptions are made on how guest performs hypercalls.
Userspace hypervisors are supported as well as kvm.

How it works: Basically, we connect virtio frontend (configured by
userspace) to a backend. The backend could be a network device, or a
tun-like device. In this version I only support raw socket as a backend,
which can be bound to e.g. SR IOV, or to macvlan device.  Backend is
also configured by userspace, including vlan/mac etc.

Status:
This works for me, and I haven't see any crashes.
I have not run any benchmarks yet, compared to userspace, I expect to
see improved latency (as I save up to 4 system calls per packet) but not
bandwidth/CPU (as TSO and interrupt mitigation are not supported).

Features that I plan to look at in the future:
- TSO
- interrupt mitigation
- zero copy

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 MAINTAINERS                |   10 +
 arch/x86/kvm/Kconfig       |    1 +
 drivers/Makefile           |    1 +
 drivers/vhost/Kconfig      |   11 +
 drivers/vhost/Makefile     |    2 +
 drivers/vhost/net.c        |  429 ++++++++++++++++++++++++++++
 drivers/vhost/vhost.c      |  664 ++++++++++++++++++++++++++++++++++++++++++++
 drivers/vhost/vhost.h      |  108 +++++++
 include/linux/Kbuild       |    1 +
 include/linux/miscdevice.h |    1 +
 include/linux/vhost.h      |  100 +++++++
 11 files changed, 1328 insertions(+), 0 deletions(-)
 create mode 100644 drivers/vhost/Kconfig
 create mode 100644 drivers/vhost/Makefile
 create mode 100644 drivers/vhost/net.c
 create mode 100644 drivers/vhost/vhost.c
 create mode 100644 drivers/vhost/vhost.h
 create mode 100644 include/linux/vhost.h

diff --git a/MAINTAINERS b/MAINTAINERS
index b1114cf..de4587f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5431,6 +5431,16 @@ S:	Maintained
 F:	Documentation/filesystems/vfat.txt
 F:	fs/fat/
 
+VIRTIO HOST (VHOST)
+P:	Michael S. Tsirkin
+M:	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 bc4205d..1551ae1 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -105,6 +105,7 @@ 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..d955406
--- /dev/null
+++ b/drivers/vhost/Kconfig
@@ -0,0 +1,11 @@
+config VHOST_NET
+	tristate "Host kernel accelerator for virtio net"
+	depends on NET && EVENTFD
+	---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..64d0c13
--- /dev/null
+++ b/drivers/vhost/net.c
@@ -0,0 +1,429 @@
+/* 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 <net/sock.h>
+
+#include "vhost.h"
+
+enum {
+	VHOST_NET_VQ_RX = 0,
+	VHOST_NET_VQ_TX = 1,
+	VHOST_NET_VQ_MAX = 2,
+};
+
+struct vhost_net {
+	struct vhost_dev dev;
+	struct vhost_virtqueue vqs[VHOST_NET_VQ_MAX];
+	/* We use a kind of RCU to access sock 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 device mutex. */
+	struct socket *sock;
+	struct vhost_poll poll[VHOST_NET_VQ_MAX];
+};
+
+/* 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;
+	struct msghdr msg = {
+		.msg_name = NULL,
+		.msg_namelen = 0,
+		.msg_control = NULL,
+		.msg_controllen = 0,
+		.msg_iov = (struct iovec *)vq->iov + 1,
+		.msg_flags = MSG_DONTWAIT,
+	};
+	size_t len;
+	int err;
+	struct socket *sock = rcu_dereference(net->sock);
+	if (!sock || !sock_writeable(sock->sk))
+		return;
+
+	use_mm(net->dev.mm);
+	mutex_lock(&vq->mutex);
+	for (;;) {
+		head = vhost_get_vq_desc(&net->dev, vq, vq->iov, &out, &in);
+		/* Nothing new?  Wait for eventfd to tell us they refilled. */
+		if (head == vq->num)
+			break;
+		if (out <= 1 || in) {
+			vq_err(vq, "Unexpected descriptor format for TX: "
+			       "out %d, int %d\n", out, in);
+			break;
+		}
+		/* Sanity check */
+		if (vq->iov->iov_len != sizeof(struct virtio_net_hdr)) {
+			vq_err(vq, "Unexpected header len for TX: "
+			       "%ld expected %zd\n", vq->iov->iov_len,
+			       sizeof(struct virtio_net_hdr));
+			break;
+		}
+		/* Skip header. TODO: support TSO. */
+		msg.msg_iovlen = out - 1;
+		len = iov_length(vq->iov + 1, out - 1);
+		/* TODO: Check specific error and bomb out unless ENOBUFS? */
+		err = sock->ops->sendmsg(NULL, sock, &msg, len);
+		if (err < 0) {
+			vhost_discard_vq_desc(vq);
+			break;
+		}
+		if (err != len)
+			pr_err("Truncated TX packet: "
+			       " len %d != %zd\n", err, len);
+		vhost_add_used_and_trigger(vq, head,
+				     len + sizeof(struct virtio_net_hdr));
+	}
+
+	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;
+	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 + 1,
+		.msg_flags = MSG_DONTWAIT,
+	};
+
+	struct virtio_net_hdr hdr = {
+		.flags = 0,
+		.gso_type = VIRTIO_NET_HDR_GSO_NONE
+	};
+
+	size_t len;
+	int err;
+	struct socket *sock = rcu_dereference(net->sock);
+	if (!sock || skb_queue_empty(&sock->sk->sk_receive_queue))
+		return;
+
+	use_mm(net->dev.mm);
+	mutex_lock(&vq->mutex);
+
+	for (;;) {
+		head = vhost_get_vq_desc(&net->dev, vq, vq->iov, &out, &in);
+		if (head == vq->num)
+			break;
+		if (in <= 1 || out) {
+			vq_err(vq, "Unexpected descriptor format for RX: "
+			       "out %d, int %d\n",
+			       out, in);
+			break;
+		}
+		/* Sanity check */
+		if (vq->iov->iov_len != sizeof(struct virtio_net_hdr)) {
+			vq_err(vq, "Unexpected header len for RX: "
+			       "%ld expected %zd\n",
+			       vq->iov->iov_len, sizeof(struct virtio_net_hdr));
+			break;
+		}
+		/* Skip header. TODO: support TSO/mergeable rx buffers. */
+		msg.msg_iovlen = in - 1;
+		len = iov_length(vq->iov + 1, in - 1);
+		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 = copy_to_user(vq->iov->iov_base, &hdr, sizeof hdr);
+		if (err) {
+			vq_err(vq, "Unable to write vnet_hdr at addr %p: %d\n",
+			       vq->iov->iov_base, err);
+			break;
+		}
+		vhost_add_used_and_trigger(vq, head, len + sizeof hdr);
+	}
+
+	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);
+	return 0;
+}
+
+static struct socket *vhost_net_stop(struct vhost_net *n)
+{
+	struct socket *sock = n->sock;
+	rcu_assign_pointer(n->sock, NULL);
+	if (sock) {
+		vhost_poll_flush(n->poll + VHOST_NET_VQ_TX);
+		vhost_poll_flush(n->poll + VHOST_NET_VQ_RX);
+	}
+	return sock;
+}
+
+static int vhost_net_release(struct inode *inode, struct file *f)
+{
+	struct vhost_net *n = f->private_data;
+	struct socket *sock;
+
+	sock = vhost_net_stop(n);
+	vhost_dev_cleanup(&n->dev);
+	if (sock)
+		fput(sock->file);
+	kfree(n);
+	return 0;
+}
+
+static long vhost_net_set_socket(struct vhost_net *n, int fd)
+{
+	struct {
+		struct sockaddr_ll sa;
+		char  buf[MAX_ADDR_LEN];
+	} uaddr;
+	struct socket *sock, *oldsock = NULL;
+	int uaddr_len = sizeof uaddr, r;
+
+	mutex_lock(&n->dev.mutex);
+	r = vhost_dev_check_owner(&n->dev);
+	if (r)
+		goto done;
+
+	if (fd == -1) {
+		/* Disconnect from socket and device. */
+		oldsock = vhost_net_stop(n);
+		goto done;
+	}
+
+	sock = sockfd_lookup(fd, &r);
+	if (!sock) {
+		r = -ENOTSOCK;
+		goto done;
+	}
+
+	/* Parameter checking */
+	if (sock->sk->sk_type != SOCK_RAW) {
+		r = -ESOCKTNOSUPPORT;
+		goto done;
+	}
+
+	r = sock->ops->getname(sock, (struct sockaddr *)&uaddr.sa,
+			       &uaddr_len, 0);
+	if (r)
+		goto done;
+
+	if (uaddr.sa.sll_family != AF_PACKET) {
+		r = -EPFNOSUPPORT;
+		goto done;
+	}
+
+	/* start polling new socket */
+	if (sock == oldsock)
+		goto done;
+
+	if (oldsock) {
+		vhost_poll_stop(n->poll + VHOST_NET_VQ_TX);
+		vhost_poll_stop(n->poll + VHOST_NET_VQ_RX);
+	}
+	oldsock = n->sock;
+	rcu_assign_pointer(n->sock, sock);
+	vhost_poll_start(n->poll + VHOST_NET_VQ_TX, sock->file);
+	vhost_poll_start(n->poll + VHOST_NET_VQ_RX, sock->file);
+done:
+	mutex_unlock(&n->dev.mutex);
+	if (oldsock) {
+		vhost_poll_flush(n->poll + VHOST_NET_VQ_TX);
+		vhost_poll_flush(n->poll + VHOST_NET_VQ_RX);
+		vhost_poll_flush(&n->dev.vqs[VHOST_NET_VQ_TX].poll);
+		vhost_poll_flush(&n->dev.vqs[VHOST_NET_VQ_RX].poll);
+		fput(oldsock->file);
+	}
+	return r;
+}
+
+static long vhost_net_reset_owner(struct vhost_net *n)
+{
+	struct socket *sock = NULL;
+	long r;
+	mutex_lock(&n->dev.mutex);
+	r = vhost_dev_check_owner(&n->dev);
+	if (r)
+		goto done;
+	sock = vhost_net_stop(n);
+	r = vhost_dev_reset_owner(&n->dev);
+done:
+	mutex_unlock(&n->dev.mutex);
+	if (sock)
+		fput(sock->file);
+	return r;
+}
+
+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;
+	int __user *fdp = argp;
+	u32 features;
+	int fd, r;
+	switch (ioctl) {
+	case VHOST_NET_SET_SOCKET:
+		r = get_user(fd, fdp);
+		if (r < 0)
+			return r;
+		return vhost_net_set_socket(n, fd);
+	case VHOST_GET_FEATURES:
+		/* No features for now */
+		features = 0;
+		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)
+			return -EOPNOTSUPP;
+		return 0;
+	case VHOST_RESET_OWNER:
+		return vhost_net_reset_owner(n);
+	default:
+		return vhost_dev_ioctl(&n->dev, ioctl, arg);
+	}
+}
+
+#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..e14169f
--- /dev/null
+++ b/drivers/vhost/vhost.c
@@ -0,0 +1,664 @@
+/* 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/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,
+};
+
+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 user 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);
+}
+
+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;
+}
+
+/* User should have device mutex */
+long vhost_dev_check_owner(struct vhost_dev *dev)
+{
+	return dev->mm == current->mm ? 0 : -EPERM;
+}
+
+/* User should have device mutex */
+static long vhost_dev_set_owner(struct vhost_dev *dev)
+{
+	if (dev->mm)
+		return -EBUSY;
+	dev->mm = get_task_mm(current);
+	return 0;
+}
+
+/* User 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 = kmalloc(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;
+}
+
+/* User 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;
+	}
+	/* 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)
+{
+	u16 flags = 0;
+	int r = put_user(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->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)(long)a.user_addr != a.user_addr) {
+			r = -EFAULT;
+			break;
+		}
+		vq->desc = (void __user *)(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)(long)a.user_addr != a.user_addr) {
+			r = -EFAULT;
+			break;
+		}
+		vq->avail = (void __user *)(long)a.user_addr;
+		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)(long)a.user_addr != a.user_addr) {
+			r = -EFAULT;
+			break;
+		}
+		vq->used = (void __user *)(long)a.user_addr;
+		r = init_used(vq);
+		if (r)
+			break;
+		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 0;
+}
+
+long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, unsigned long arg)
+{
+	void __user *argp = (void __user *)arg;
+	long r;
+
+	mutex_lock(&d->mutex);
+	if (ioctl == VHOST_SET_OWNER) {
+		r = vhost_dev_set_owner(d);
+		goto done;
+	}
+
+	r = vhost_dev_check_owner(d);
+	if (r)
+		goto done;
+
+	switch (ioctl) {
+	case VHOST_SET_MEM_TABLE:
+		r = vhost_set_memory(d, argp);
+		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;
+}
+
+/* FIXME: this does not handle a region that spans multiple
+ * address/len pairs */
+int translate_desc(struct vhost_dev *dev, u64 addr, u32 len,
+		   struct iovec iov[], int iov_count, int iov_size,
+		   unsigned *num)
+{
+	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 (*num + iov_count >= iov_size) {
+			ret = -ENOBUFS;
+			break;
+		}
+		reg = find_region(mem, addr, len);
+		if (!reg) {
+			ret = -EFAULT;
+			break;
+		}
+		_iov = iov + iov_count + *num;
+		size = reg->memory_size - addr + reg->guest_phys_addr;
+		_iov->iov_len = min((u64)len, size);
+		_iov->iov_base = (void *)
+			(reg->userspace_addr + addr - reg->guest_phys_addr);
+		s += size;
+		addr += size;
+		++*num;
+	}
+
+	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 vq->vring.num if we're
+ * at the end. */
+static unsigned next_desc(struct vhost_virtqueue *vq, 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 vq->num;
+
+	/* 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();
+
+	if (next >= vq->num) {
+		vq_err(vq, "Desc next is %u > %u", next, vq->num);
+		return vq->num;
+	}
+
+	return next;
+}
+
+/* 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 vring_desc desc;
+	unsigned int i, head;
+	u16 last_avail_idx, idx;
+
+	/* Check it isn't doing very strange things with descriptor numbers. */
+	last_avail_idx = vq->last_avail_idx;
+	if (get_user(idx, &vq->avail->idx)) {
+		vq_err(vq, "Failed to access avail idx at %p\n",
+		       &vq->avail->idx);
+		return vq->num;
+	}
+
+	if ((u16)(idx - last_avail_idx) > vq->num) {
+		vq_err(vq, "Guest moved used index from %u to %u",
+		       last_avail_idx, idx);
+		return vq->num;
+	}
+
+	/* If there's nothing new since last we looked, return invalid. */
+	if (idx == last_avail_idx)
+		return vq->num;
+
+	/* 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",
+		       idx, &vq->avail->ring[last_avail_idx % vq->num]);
+		return vq->num;
+	}
+
+	/* If their number is silly, that's a fatal mistake. */
+	if (head >= vq->num) {
+		vq_err(vq, "Guest says index %u > %u is available",
+		       head, vq->num);
+		return vq->num;
+	}
+
+	vq->last_avail_idx++;
+
+	/* When we start there are none of either input nor output. */
+	*out_num = *in_num = 0;
+
+	i = head;
+	do {
+		unsigned *num;
+		unsigned iov_count;
+		if (copy_from_user(&desc, vq->desc + i, sizeof desc)) {
+			vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
+			       i, vq->desc + i);
+			return vq->num;
+		}
+		/* If this is an input descriptor, increment that count. */
+		if (desc.flags & VRING_DESC_F_WRITE) {
+			num = in_num;
+			iov_count = *out_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;
+			}
+			num = out_num;
+			iov_count = *in_num;
+		}
+		if (translate_desc(dev, desc.addr, desc.len, iov, iov_count,
+				   VHOST_NET_MAX_SG, num)) {
+			vq_err(vq, "Failed to translate descriptor: idx %d\n",
+			       i);
+			return vq->num;
+		}
+
+		/* If we've got too many, that implies a descriptor loop. */
+		if (*out_num + *in_num > vq->num) {
+			vq_err(vq, "Looped descriptor: idx %d\n", i);
+			return vq->num;
+		}
+	} while ((i = next_desc(vq, &desc)) != vq->num);
+
+	vq->inflight++;
+	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--;
+	vq->inflight--;
+}
+
+/* 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;
+	}
+	vq->last_used_idx++;
+	vq->inflight--;
+	return 0;
+}
+
+/* This actually sends the interrupt for this virtqueue */
+void vhost_trigger_irq(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->inflight)
+		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_virtqueue *vq,
+				unsigned int head, int len)
+{
+	vhost_add_used(vq, head, len);
+	vhost_trigger_irq(vq);
+}
+
+int vhost_init(void)
+{
+	vhost_workqueue = create_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..7f7ffcd
--- /dev/null
+++ b/drivers/vhost/vhost.h
@@ -0,0 +1,108 @@
+#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>
+
+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);
+
+/* 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 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;
+
+	/* Last index we used. */
+	u16 last_used_idx;
+
+	/* Outstanding buffers */
+	unsigned int inflight;
+
+	/* Is this blocked? */
+	bool blocked;
+
+	struct iovec iov[VHOST_NET_MAX_SG];
+
+} ____cacheline_aligned;
+
+struct vhost_dev {
+	/* Readers use RCU to access memory table pointer.
+	 * Writers use mutex below.*/
+	struct vhost_memory *memory;
+	struct mm_struct *mm;
+	struct vhost_virtqueue *vqs;
+	int nvqs;
+	struct mutex mutex;
+};
+
+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);
+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_virtqueue *);
+void vhost_add_used_and_trigger(struct vhost_virtqueue *,
+				unsigned int head, int len);
+
+int vhost_init(void);
+void vhost_cleanup(void);
+
+#define vq_err(vq, fmt, ...) do {                                  \
+		printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__);       \
+		if ((vq)->error_ctx)                               \
+				eventfd_signal((vq)->error_ctx, 1);\
+	} while (0)
+
+#endif
diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index dec2f18..975df9a 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -360,6 +360,7 @@ 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 0521177..781a8bb 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..9ec6d5f
--- /dev/null
+++ b/include/linux/vhost.h
@@ -0,0 +1,100 @@
+#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;
+};
+
+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 padding; /* read/write protection? */
+};
+
+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 must be zero. */
+#define VHOST_GET_FEATURES	_IOR(VHOST_VIRTIO, 0x00, __u32)
+#define VHOST_ACK_FEATURES	_IOW(VHOST_VIRTIO, 0x00, __u32)
+
+/* 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)
+
+/* 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 */
+#define VHOST_SET_VRING_USED _IOW(VHOST_VIRTIO, 0x12, struct vhost_vring_addr)
+/* Available structure address */
+#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)
+
+/* 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 device to a raw socket. The socket must be already
+ * bound to an ethernet device, this device will be used for transmit.
+ * Pass -1 to unbind from the socket and the transmit device.
+ * This can be used to stop the device (e.g. for migration). */
+#define VHOST_NET_SET_SOCKET _IOW(VHOST_VIRTIO, 0x30, int)
+
+#endif
-- 
1.6.2.5

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Rusty Russell]

On Thu, 20 Aug 2009 12:33:09 am Michael S. Tsirkin wrote:
> What it is: vhost net is a character device that can be used to reduce
> the number of system calls involved in virtio networking.
> Existing virtio net code is used in the guest without modification.

...

> +config VHOST_NET
> +	tristate "Host kernel accelerator for virtio net"
> +	depends on NET && EVENTFD
> +	---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.

Just want to note that the patch explanation and the Kconfig help text are
exceptional examples of reader-oriented text.  Nice!

> +		/* Sanity check */
> +		if (vq->iov->iov_len != sizeof(struct virtio_net_hdr)) {
> +			vq_err(vq, "Unexpected header len for TX: "
> +			       "%ld expected %zd\n", vq->iov->iov_len,
> +			       sizeof(struct virtio_net_hdr));
> +			break;
> +		}

OK, this check, which is in the qemu version, is *wrong*.  There should be
no assumption on sg boundaries.  For example, the guest should be able to
put the virtio_net_hdr in the front of the skbuf data if there is room.

You should try to explicitly "consume" sizeof(struct virtio_net_hdr) of the
iov, and if fail, do this message.  You can skip the out <= 1 test then,
too.

Anyway, I really prefer vq->iov[0]. to vq->iov-> here.

> +		/* Sanity check */
> +		if (vq->iov->iov_len != sizeof(struct virtio_net_hdr)) {
> +			vq_err(vq, "Unexpected header len for RX: "
> +			       "%ld expected %zd\n",
> +			       vq->iov->iov_len, sizeof(struct virtio_net_hdr));
> +			break;

Here too.

> +	u32 __user *featurep = argp;
> +	int __user *fdp = argp;
> +	u32 features;
> +	int fd, r;
> +	switch (ioctl) {
> +	case VHOST_NET_SET_SOCKET:
> +		r = get_user(fd, fdp);
> +		if (r < 0)
> +			return r;
> +		return vhost_net_set_socket(n, fd);
> +	case VHOST_GET_FEATURES:
> +		/* No features for now */
> +		features = 0;
> +		return put_user(features, featurep);

We may well get more than 32 feature bits, at least for virtio_net, which will
force us to do some trickery in virtio_pci.  I'd like to avoid that here,
though it's kind of ugly.  We'd need VHOST_GET_FEATURES (and ACK) to take a
struct like:

	u32 feature_size;
	u32 features[];

> +int vhost_net_init(void)

static?

> +void vhost_net_exit(void)

static?

> +/* Start polling a file. We add ourselves to file's wait queue. The user must
> + * keep a reference to a file until after vhost_poll_stop is called. */

I experienced minor confusion from the comments in this file.  Where you said
"user" I think "caller".  No biggie though.

> +	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;

Not sure I understand why there are two regions to start?

> +	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->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;

Ah, this is my fault.  I didn't expose the last_avail_idx in the ring
because the other side doesn't need it; but without it the ring state is not
fully observable from outside (no external save / restore!).

I have a patch which published these indices (we have room), see:
	http://ozlabs.org/~rusty/kernel/rr-2009-08-12-1/virtio:ring-publish-indices.patch

Perhaps we should use that mechanism instead?  We don't actually have to
offer the feature (we don't care about the guest state), but it's nice as
documentation.  I've been waiting for an excuse to use that patch.

> +long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, unsigned long arg)
> +{
> +	void __user *argp = (void __user *)arg;
> +	long r;
> +
> +	mutex_lock(&d->mutex);
> +	if (ioctl == VHOST_SET_OWNER) {
> +		r = vhost_dev_set_owner(d);
> +		goto done;
> +	}
> +
> +	r = vhost_dev_check_owner(d);

You can do a VHOST_SET_OWNER without being the owner?  So really,
the -EPERM from all the vhost_dev_check_owner() is not a security thing,
but a "I don't think you mean to do that" thing?

If so, a comment above it might help?

> +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 */

Ah, you actually mean "this code has been carefully cache-optimized for the
common case" :)

> +/* FIXME: this does not handle a region that spans multiple
> + * address/len pairs */
> +int translate_desc(struct vhost_dev *dev, u64 addr, u32 len,
> +		   struct iovec iov[], int iov_count, int iov_size,
> +		   unsigned *num)
> +{
> +	const struct vhost_memory_region *reg;
> +	struct vhost_memory *mem;
> +	struct iovec *_iov;
> +	u64 s = 0;
> +	int ret = 0;

Would this be neater if it returned the num iovecs used?  And offsetting
iov in the caller, rather than passing iov_count?

> +	/* If their number is silly, that's a fatal mistake. */
> +	if (head >= vq->num) {
> +		vq_err(vq, "Guest says index %u > %u is available",
> +		       head, vq->num);
> +		return vq->num;
> +	}

Not a fatal mistake in this code/

> +	vq->inflight++;

vq->inflight was a brain fart in the old lguest code.  See
commit ebf9a5a99c1a464afe0b4dfa64416fc8b273bc5c.

Also, see other fixes to the lguest launcher since then which might
be relevant to this code:
	lguest: get more serious about wmb() in example Launcher code
	lguest: clean up length-used value in example launcher

> +	/* If they don't want an interrupt, don't send one, unless empty. */
> +	if ((flags & VRING_AVAIL_F_NO_INTERRUPT) && vq->inflight)
> +		return;

And I wouldn't support notify on empty at all, TBH.  It should
definitely be conditional on the guest accepting the NOTIFY_ON_EMPTY
feature.

> +/* The virtqueue structure describes a queue attached to a device. */
> +struct vhost_virtqueue {
...
> +} ____cacheline_aligned;

Really?  I'd want to see numbers on this one.  False sharing vs. more cache
utilization.

> +#define vq_err(vq, fmt, ...) do {                                  \
> +		printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__);       \
> +		if ((vq)->error_ctx)                               \
> +				eventfd_signal((vq)->error_ctx, 1);\
> +	} while (0)

Mmm... guests should not be able to create unlimited printks in the host.

But really, nothing major to object to in here...

Thanks!
Rusty.

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Michael S. Tsirkin]

Thanks for the comments, I'll work on them ASAP.
Answers to questions and more comments below.

On Tue, Aug 25, 2009 at 09:40:40PM +0930, Rusty Russell wrote:
> On Thu, 20 Aug 2009 12:33:09 am Michael S. Tsirkin wrote:
> > What it is: vhost net is a character device that can be used to reduce
> > the number of system calls involved in virtio networking.
> > Existing virtio net code is used in the guest without modification.
> 
> ...
> 
> > +config VHOST_NET
> > +	tristate "Host kernel accelerator for virtio net"
> > +	depends on NET && EVENTFD
> > +	---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.
> 
> Just want to note that the patch explanation and the Kconfig help text are
> exceptional examples of reader-oriented text.  Nice!

High praise indeed from the author of the lguest Quest :).

> > +		/* Sanity check */
> > +		if (vq->iov->iov_len != sizeof(struct virtio_net_hdr)) {
> > +			vq_err(vq, "Unexpected header len for TX: "
> > +			       "%ld expected %zd\n", vq->iov->iov_len,
> > +			       sizeof(struct virtio_net_hdr));
> > +			break;
> > +		}
> 
> OK, this check, which is in the qemu version, is *wrong*.  There should be
> no assumption on sg boundaries.  For example, the guest should be able to
> put the virtio_net_hdr in the front of the skbuf data if there is room.
> 
> You should try to explicitly "consume" sizeof(struct virtio_net_hdr) of the
> iov, and if fail, do this message.  You can skip the out <= 1 test then,
> too.
> 
> Anyway, I really prefer vq->iov[0]. to vq->iov-> here.

I'll fix that. Probably should fix qemu as well.

> > +		/* Sanity check */
> > +		if (vq->iov->iov_len != sizeof(struct virtio_net_hdr)) {
> > +			vq_err(vq, "Unexpected header len for RX: "
> > +			       "%ld expected %zd\n",
> > +			       vq->iov->iov_len, sizeof(struct virtio_net_hdr));
> > +			break;
> 
> Here too.
> 
> > +	u32 __user *featurep = argp;
> > +	int __user *fdp = argp;
> > +	u32 features;
> > +	int fd, r;
> > +	switch (ioctl) {
> > +	case VHOST_NET_SET_SOCKET:
> > +		r = get_user(fd, fdp);
> > +		if (r < 0)
> > +			return r;
> > +		return vhost_net_set_socket(n, fd);
> > +	case VHOST_GET_FEATURES:
> > +		/* No features for now */
> > +		features = 0;
> > +		return put_user(features, featurep);
> 
> We may well get more than 32 feature bits, at least for virtio_net, which will
> force us to do some trickery in virtio_pci.  I'd like to avoid that here,
> though it's kind of ugly.  We'd need VHOST_GET_FEATURES (and ACK) to take a
> struct like:
> 
> 	u32 feature_size;
> 	u32 features[];

Do you feel just making it 64 bit won't be enough?  How about 128 bit?

> > +int vhost_net_init(void)
> 
> static?
> 
> > +void vhost_net_exit(void)
> 
> static?

Good catch.

> > +/* Start polling a file. We add ourselves to file's wait queue. The user must
> > + * keep a reference to a file until after vhost_poll_stop is called. */
> 
> I experienced minor confusion from the comments in this file.  Where you said
> "user" I think "caller".  No biggie though.
> 
> > +	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;
> 
> Not sure I understand why there are two regions to start?

We are trying to cover a whole 2^64 range here.  It's size does not fit
in a single 64 bit length value.  I could special case 0 length to mean
2^64, but decided against it.

> > +	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->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;
> 
> Ah, this is my fault.  I didn't expose the last_avail_idx in the ring
> because the other side doesn't need it; but without it the ring state is not
> fully observable from outside (no external save / restore!).
> 
> I have a patch which published these indices (we have room), see:
> 	http://ozlabs.org/~rusty/kernel/rr-2009-08-12-1/virtio:ring-publish-indices.patch
> 
> Perhaps we should use that mechanism instead?  We don't actually have to
> offer the feature (we don't care about the guest state), but it's nice as
> documentation.  I've been waiting for an excuse to use that patch.

Good idea and might be handy for optimizations as well, and I
would have used it if it was there.  I'd like to support existing guests
in vhost though, so I think we need to support this ioctl for now.

> > +long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, unsigned long arg)
> > +{
> > +	void __user *argp = (void __user *)arg;
> > +	long r;
> > +
> > +	mutex_lock(&d->mutex);
> > +	if (ioctl == VHOST_SET_OWNER) {
> > +		r = vhost_dev_set_owner(d);
> > +		goto done;
> > +	}
> > +
> > +	r = vhost_dev_check_owner(d);
> 
> You can do a VHOST_SET_OWNER without being the owner?

Only if no one else is the owner.  It has a mutual exclusion
mechanism.

> So really,
> the -EPERM from all the vhost_dev_check_owner() is not a security thing,
> but a "I don't think you mean to do that" thing?

Mostly that.  I started by assuming that an open fd can't be
passed around at all, but talking with management guys here,
they really like being able to open fds and pass them around
through unix domain sockets.

Since using this fd from multiple processes does not work well,
I decided to make this explicit in the interface.  I find it quite
possible that there's no security thing here, but this is just a simpler
model to think about than guessing whether some crash is exploitable or
not.

> If so, a comment above it might help?

Yes.

> > +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 */
> 
> Ah, you actually mean "this code has been carefully cache-optimized for the
> common case" :)
> 
> > +/* FIXME: this does not handle a region that spans multiple
> > + * address/len pairs */
> > +int translate_desc(struct vhost_dev *dev, u64 addr, u32 len,
> > +		   struct iovec iov[], int iov_count, int iov_size,
> > +		   unsigned *num)
> > +{
> > +	const struct vhost_memory_region *reg;
> > +	struct vhost_memory *mem;
> > +	struct iovec *_iov;
> > +	u64 s = 0;
> > +	int ret = 0;
> 
> Would this be neater if it returned the num iovecs used?  And offsetting
> iov in the caller, rather than passing iov_count?

iov_size would have to be tweaked instead as well.

> > +	/* If their number is silly, that's a fatal mistake. */
> > +	if (head >= vq->num) {
> > +		vq_err(vq, "Guest says index %u > %u is available",
> > +		       head, vq->num);
> > +		return vq->num;
> > +	}
> 
> Not a fatal mistake in this code/
> 
> > +	vq->inflight++;
> 
> vq->inflight was a brain fart in the old lguest code.  See
> commit ebf9a5a99c1a464afe0b4dfa64416fc8b273bc5c.

I wondered about that. OK.

> Also, see other fixes to the lguest launcher since then which might
> be relevant to this code:
> 	lguest: get more serious about wmb() in example Launcher code
> 	lguest: clean up length-used value in example launcher

I'll go over them, thanks!
I did look over barriers, but this is tricky stuff.

> > +	/* If they don't want an interrupt, don't send one, unless empty. */
> > +	if ((flags & VRING_AVAIL_F_NO_INTERRUPT) && vq->inflight)
> > +		return;
> 
> And I wouldn't support notify on empty at all, TBH.

If I don't, virtio net in guest uses a timer, which might be expensive.
Will need to check what this does.

>  It should
> definitely be conditional on the guest accepting the NOTIFY_ON_EMPTY
> feature.

Good point.

> > +/* The virtqueue structure describes a queue attached to a device. */
> > +struct vhost_virtqueue {
> ...
> > +} ____cacheline_aligned;
> 
> Really?  I'd want to see numbers on this one.  False sharing vs. more cache
> utilization.

I don't yet want to focus on micro optimizations.  What's your guess?
That it's better without? I'll kill it then ...


> > +#define vq_err(vq, fmt, ...) do {                                  \
> > +		printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__);       \
> > +		if ((vq)->error_ctx)                               \
> > +				eventfd_signal((vq)->error_ctx, 1);\
> > +	} while (0)
> 
> Mmm... guests should not be able to create unlimited printks in the host.

Yes, but handy for debugging :)
I guess I'll just make it use pr_debug instead?

> But really, nothing major to object to in here...
> 
> Thanks!
> Rusty.

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Michael S. Tsirkin]

On Tue, Aug 25, 2009 at 04:16:34PM +0300, Michael S. Tsirkin wrote:
> > > +	/* If they don't want an interrupt, don't send one, unless empty. */
> > > +	if ((flags & VRING_AVAIL_F_NO_INTERRUPT) && vq->inflight)
> > > +		return;
> > 
> > And I wouldn't support notify on empty at all, TBH.
> 
> If I don't, virtio net in guest uses a timer, which might be expensive.
> Will need to check what this does.
> 
> >  It should
> > definitely be conditional on the guest accepting the NOTIFY_ON_EMPTY
> > feature.

lguest does not do it this way though, do it?

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Rusty Russell]

On Thu, 27 Aug 2009 02:26:55 am Michael S. Tsirkin wrote:
> On Tue, Aug 25, 2009 at 04:16:34PM +0300, Michael S. Tsirkin wrote:
> > > > +	/* If they don't want an interrupt, don't send one, unless empty. */
> > > > +	if ((flags & VRING_AVAIL_F_NO_INTERRUPT) && vq->inflight)
> > > > +		return;
> > > 
> > > And I wouldn't support notify on empty at all, TBH.
> > 
> > If I don't, virtio net in guest uses a timer, which might be expensive.
> > Will need to check what this does.
> > 
> > >  It should
> > > definitely be conditional on the guest accepting the NOTIFY_ON_EMPTY
> > > feature.
> 
> lguest does not do it this way though, do it?

Does when a patch in my current queue is applied though.

Thanks,
Rusty.

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Michael S. Tsirkin]

On Tue, Aug 25, 2009 at 09:40:40PM +0930, Rusty Russell wrote:
> > +	u32 __user *featurep = argp;
> > +	int __user *fdp = argp;
> > +	u32 features;
> > +	int fd, r;
> > +	switch (ioctl) {
> > +	case VHOST_NET_SET_SOCKET:
> > +		r = get_user(fd, fdp);
> > +		if (r < 0)
> > +			return r;
> > +		return vhost_net_set_socket(n, fd);
> > +	case VHOST_GET_FEATURES:
> > +		/* No features for now */
> > +		features = 0;
> > +		return put_user(features, featurep);
> 
> We may well get more than 32 feature bits, at least for virtio_net, which will
> force us to do some trickery in virtio_pci.

Unlike PCI, if we ever run out of bits we can just
add FEATURES_EXTENDED ioctl, no need for trickery.

>  I'd like to avoid that here,
> though it's kind of ugly.  We'd need VHOST_GET_FEATURES (and ACK) to take a
> struct like:
> 
> 	u32 feature_size;
> 	u32 features[];


Thinking about this proposal some more, how will the guest
determine the size to supply the GET_FEATURES ioctl?

Since we are a bit tight in 32 bit space already,
let's just use a 64 bit integer and be done with it?
Right?

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Arnd Bergmann]

On Tuesday 25 August 2009, Michael S. Tsirkin wrote:
> >  I'd like to avoid that here,
> > though it's kind of ugly.  We'd need VHOST_GET_FEATURES (and ACK) to take a
> > struct like:
> > 
> >       u32 feature_size;
> >       u32 features[];

Hmm, variable length ioctl arguments, I'd rather not go there.
The ioctl infrastructure already has a length argument encoded
in the ioctl number. We can use that if we need more, e.g.

/* now */
#define VHOST_GET_FEATURES     _IOR(VHOST_VIRTIO, 0x00, __u64)
/*
 * uncomment if we run out of feature bits:

struct vhost_get_features2 {
	__u64 bits[2];
};
#define VHOST_GET_FEATURES2     _IOR(VHOST_VIRTIO, 0x00, \
			struct  vhost_get_features2)
 */

> Thinking about this proposal some more, how will the guest
> determine the size to supply the GET_FEATURES ioctl?

Wait, the *guest*?

Maybe I misunderstood something in a major way here, but
I expected the features to be negotiated between host
user space (qemu) and host kernel, as well as between
guest and qemu (as they are already), but never between
guest and kernel.

I would certainly expect the bits to be distinct from
the virtio-net feature bits. E.g. stuff like TAP frame
format opposed to TCP socket frame format (length+date)
is something we need to negotiate here but that the
guest does not care about.

> Since we are a bit tight in 32 bit space already,
> let's just use a 64 bit integer and be done with it?

Can't hurt, but don't use a struct unless you think
we are going to need more than 64 bits.

	Arnd <><

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Michael S. Tsirkin]

On Wed, Aug 26, 2009 at 03:40:59PM +0200, Arnd Bergmann wrote:
> On Tuesday 25 August 2009, Michael S. Tsirkin wrote:
> > >  I'd like to avoid that here,
> > > though it's kind of ugly.  We'd need VHOST_GET_FEATURES (and ACK) to take a
> > > struct like:
> > > 
> > >       u32 feature_size;
> > >       u32 features[];
> 
> Hmm, variable length ioctl arguments, I'd rather not go there.
> The ioctl infrastructure already has a length argument encoded
> in the ioctl number. We can use that if we need more, e.g.
> 
> /* now */
> #define VHOST_GET_FEATURES     _IOR(VHOST_VIRTIO, 0x00, __u64)
> /*
>  * uncomment if we run out of feature bits:
> 
> struct vhost_get_features2 {
> 	__u64 bits[2];
> };
> #define VHOST_GET_FEATURES2     _IOR(VHOST_VIRTIO, 0x00, \
> 			struct  vhost_get_features2)
>  */
> 
> > Thinking about this proposal some more, how will the guest
> > determine the size to supply the GET_FEATURES ioctl?
> 
> Wait, the *guest*?

Sorry. the userspace hypervisor.

> Maybe I misunderstood something in a major way here, but
> I expected the features to be negotiated between host
> user space (qemu) and host kernel, as well as between
> guest and qemu (as they are already), but never between
> guest and kernel.

Yes.

> I would certainly expect the bits to be distinct from
> the virtio-net feature bits. E.g. stuff like TAP frame
> format opposed to TCP socket frame format (length+date)
> is something we need to negotiate here but that the
> guest does not care about.

My idea is to use virtio format for things I share with virtio (e.g.
mergeable buffers).  Since we are a kind of transport, I thought that I
will use the transport bits, that is bits 28 and up for vhost things.

> > Since we are a bit tight in 32 bit space already,
> > let's just use a 64 bit integer and be done with it?
> 
> Can't hurt, but don't use a struct unless you think
> we are going to need more than 64 bits.
> 
> 	Arnd <><

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Michael S. Tsirkin]

On Wed, Aug 26, 2009 at 03:40:59PM +0200, Arnd Bergmann wrote:
> On Tuesday 25 August 2009, Michael S. Tsirkin wrote:
> > >  I'd like to avoid that here,
> > > though it's kind of ugly.  We'd need VHOST_GET_FEATURES (and ACK) to take a
> > > struct like:
> > > 
> > >       u32 feature_size;
> > >       u32 features[];
> 
> Hmm, variable length ioctl arguments, I'd rather not go there.
> The ioctl infrastructure already has a length argument encoded
> in the ioctl number. We can use that if we need more, e.g.
> 
> /* now */
> #define VHOST_GET_FEATURES     _IOR(VHOST_VIRTIO, 0x00, __u64)
> /*
>  * uncomment if we run out of feature bits:
> 
> struct vhost_get_features2 {
> 	__u64 bits[2];
> };
> #define VHOST_GET_FEATURES2     _IOR(VHOST_VIRTIO, 0x00, \
> 			struct  vhost_get_features2)
>  */


I thought so, too. Rusty, agree?

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Rusty Russell]

On Thu, 27 Aug 2009 07:40:26 pm Michael S. Tsirkin wrote:
> On Wed, Aug 26, 2009 at 03:40:59PM +0200, Arnd Bergmann wrote:
> > On Tuesday 25 August 2009, Michael S. Tsirkin wrote:
> > > >  I'd like to avoid that here,
> > > > though it's kind of ugly.  We'd need VHOST_GET_FEATURES (and ACK) to take a
> > > > struct like:
> > > > 
> > > >       u32 feature_size;
> > > >       u32 features[];
> > 
> > Hmm, variable length ioctl arguments, I'd rather not go there.
> > The ioctl infrastructure already has a length argument encoded
> > in the ioctl number. We can use that if we need more, e.g.
> > 
> > /* now */
> > #define VHOST_GET_FEATURES     _IOR(VHOST_VIRTIO, 0x00, __u64)
> > /*
> >  * uncomment if we run out of feature bits:
> > 
> > struct vhost_get_features2 {
> > 	__u64 bits[2];
> > };
> > #define VHOST_GET_FEATURES2     _IOR(VHOST_VIRTIO, 0x00, \
> > 			struct  vhost_get_features2)
> >  */
> 
> 
> I thought so, too. Rusty, agree?

Yep, am convinced.  Make it u64 to stop us having to do this tomorrow, then
we can always extend later.

Thanks,
Rusty.

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Michael S. Tsirkin]

On Tue, Aug 25, 2009 at 09:40:40PM +0930, Rusty Russell wrote:
> Also, see other fixes to the lguest launcher since then which might
> be relevant to this code:
> 	lguest: get more serious about wmb() in example Launcher code

Heh, this just gets one step closer to a real wmb.  I just used the
correct code from linux, so I think nothing needs to be done in vhost.
Apropos this change in lguest: why is a compiler barrier sufficient? The
comment says devices are run in separate threads (presumably from
guest?), if so don't you need to tell CPU that there's a barrier as
well?

> 	lguest: clean up length-used value in example launcher

OK, fixing that.

Thanks!

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Rusty Russell]

On Thu, 27 Aug 2009 08:15:18 pm Michael S. Tsirkin wrote:
> On Tue, Aug 25, 2009 at 09:40:40PM +0930, Rusty Russell wrote:
> > Also, see other fixes to the lguest launcher since then which might
> > be relevant to this code:
> > 	lguest: get more serious about wmb() in example Launcher code
> 
> Heh, this just gets one step closer to a real wmb.  I just used the
> correct code from linux, so I think nothing needs to be done in vhost.
> Apropos this change in lguest: why is a compiler barrier sufficient? The
> comment says devices are run in separate threads (presumably from
> guest?), if so don't you need to tell CPU that there's a barrier as
> well?

Yep, but x86 only :)  The kernel uses a real insn if XMM/XMM2, but I don't
know if userspace needs that.  I just use compiler barriers.

Thanks,
Rusty.

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Re: [PATCHv4 2/2] vhost_net: a kernel-level virtio server

[Michael S. Tsirkin]

On Thu, Aug 27, 2009 at 08:40:02PM +0930, Rusty Russell wrote:
> On Thu, 27 Aug 2009 08:15:18 pm Michael S. Tsirkin wrote:
> > On Tue, Aug 25, 2009 at 09:40:40PM +0930, Rusty Russell wrote:
> > > Also, see other fixes to the lguest launcher since then which might
> > > be relevant to this code:
> > > 	lguest: get more serious about wmb() in example Launcher code
> > 
> > Heh, this just gets one step closer to a real wmb.  I just used the
> > correct code from linux, so I think nothing needs to be done in vhost.
> > Apropos this change in lguest: why is a compiler barrier sufficient? The
> > comment says devices are run in separate threads (presumably from
> > guest?), if so don't you need to tell CPU that there's a barrier as
> > well?
> 
> Yep, but x86 only :)

Okay, writes are ordered them. But mb() orders reads as well,
so it'll have to have a real one IMO, even in userspace?

>  The kernel uses a real insn if XMM/XMM2, but I don't
> know if userspace needs that.  I just use compiler barriers.
> 
> Thanks,
> Rusty.

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