Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Tiwei Bie <tiwei.bie@intel.com>
To:     mst@redhat.com, jasowang@redhat.com, alex.williamson@redhat.com,
        maxime.coquelin@redhat.com
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        dan.daly@intel.com, cunming.liang@intel.com,
        zhihong.wang@intel.com, lingshan.zhu@intel.com, tiwei.bie@intel.com
Subject: [PATCH v4] vhost: introduce mdev based hardware backend
Date:   Thu, 31 Oct 2019 22:01:14 +0800
Message-Id: <20191031140114.25615-1-tiwei.bie@intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

This patch introduces a mdev based hardware vhost backend.
This backend is built on top of the same abstraction used
in virtio-mdev and provides a generic vhost interface for
userspace to accelerate the virtio devices in guest.

This backend is implemented as a mdev device driver on top
of the same mdev device ops used in virtio-mdev but using
a different mdev class id, and it will register the device
as a VFIO device for userspace to use. Userspace can setup
the IOMMU with the existing VFIO container/group APIs and
then get the device fd with the device name. After getting
the device fd of this device, userspace can use vhost ioctls
to setup the backend.

Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
---
This patch depends on below series:
https://lkml.org/lkml/2019/10/30/62

v3 -> v4:
- Rebase on top of virtio-mdev series v6;
- Some minor tweaks and improvements;

v2 -> v3:
- Fix the return value (Jason);
- Don't cache unnecessary information in vhost-mdev (Jason);
- Get rid of the memset in open (Jason);
- Add comments for VHOST_SET_MEM_TABLE, ... (Jason);
- Filter out unsupported features in vhost-mdev (Jason);
- Add _GET_DEVICE_ID ioctl (Jason);
- Add _GET_CONFIG/_SET_CONFIG ioctls (Jason);
- Drop _GET_QUEUE_NUM ioctl (Jason);
- Fix the copy-paste errors in _IOW/_IOR usage;
- Some minor fixes and improvements;

v1 -> v2:
- Replace _SET_STATE with _SET_STATUS (MST);
- Check status bits at each step (MST);
- Report the max ring size and max number of queues (MST);
- Add missing MODULE_DEVICE_TABLE (Jason);
- Only support the network backend w/o multiqueue for now;
- Some minor fixes and improvements;
- Rebase on top of virtio-mdev series v4;

RFC v4 -> v1:
- Implement vhost-mdev as a mdev device driver directly and
  connect it to VFIO container/group. (Jason);
- Pass ring addresses as GPAs/IOVAs in vhost-mdev to avoid
  meaningless HVA->GPA translations (Jason);

RFC v3 -> RFC v4:
- Build vhost-mdev on top of the same abstraction used by
  virtio-mdev (Jason);
- Introduce vhost fd and pass VFIO fd via SET_BACKEND ioctl (MST);

RFC v2 -> RFC v3:
- Reuse vhost's ioctls instead of inventing a VFIO regions/irqs
  based vhost protocol on top of vfio-mdev (Jason);

RFC v1 -> RFC v2:
- Introduce a new VFIO device type to build a vhost protocol
  on top of vfio-mdev;

 drivers/vfio/mdev/mdev_core.c    |  20 ++
 drivers/vfio/mdev/mdev_private.h |   1 +
 drivers/vhost/Kconfig            |  12 +
 drivers/vhost/Makefile           |   3 +
 drivers/vhost/mdev.c             | 556 +++++++++++++++++++++++++++++++
 include/linux/mdev.h             |   5 +
 include/uapi/linux/vhost.h       |  18 +
 include/uapi/linux/vhost_types.h |   8 +
 8 files changed, 623 insertions(+)
 create mode 100644 drivers/vhost/mdev.c

diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
index 22ca589750d8..109dbac01a8f 100644
--- a/drivers/vfio/mdev/mdev_core.c
+++ b/drivers/vfio/mdev/mdev_core.c
@@ -96,6 +96,26 @@ mdev_get_virtio_ops(struct mdev_device *mdev)
 }
 EXPORT_SYMBOL(mdev_get_virtio_ops);
 
+/* Specify the vhost device ops for the mdev device, this
+ * must be called during create() callback for vhost mdev device.
+ */
+void mdev_set_vhost_ops(struct mdev_device *mdev,
+			const struct virtio_mdev_device_ops *vhost_ops)
+{
+	mdev_set_class(mdev, MDEV_CLASS_ID_VHOST);
+	mdev->vhost_ops = vhost_ops;
+}
+EXPORT_SYMBOL(mdev_set_vhost_ops);
+
+/* Get the vhost device ops for the mdev device. */
+const struct virtio_mdev_device_ops *
+mdev_get_vhost_ops(struct mdev_device *mdev)
+{
+	WARN_ON(mdev->class_id != MDEV_CLASS_ID_VHOST);
+	return mdev->vhost_ops;
+}
+EXPORT_SYMBOL(mdev_get_vhost_ops);
+
 struct device *mdev_dev(struct mdev_device *mdev)
 {
 	return &mdev->dev;
diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h
index 7b47890c34e7..5597c846e52f 100644
--- a/drivers/vfio/mdev/mdev_private.h
+++ b/drivers/vfio/mdev/mdev_private.h
@@ -40,6 +40,7 @@ struct mdev_device {
 	union {
 		const struct vfio_mdev_device_ops *vfio_ops;
 		const struct virtio_mdev_device_ops *virtio_ops;
+		const struct virtio_mdev_device_ops *vhost_ops;
 	};
 };
 
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 3d03ccbd1adc..062cada28f89 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -34,6 +34,18 @@ config VHOST_VSOCK
 	To compile this driver as a module, choose M here: the module will be called
 	vhost_vsock.
 
+config VHOST_MDEV
+	tristate "Vhost driver for Mediated devices"
+	depends on EVENTFD && VFIO && VFIO_MDEV
+	select VHOST
+	default n
+	---help---
+	This kernel module can be loaded in host kernel to accelerate
+	guest virtio devices with the mediated device based backends.
+
+	To compile this driver as a module, choose M here: the module will
+	be called vhost_mdev.
+
 config VHOST
 	tristate
 	---help---
diff --git a/drivers/vhost/Makefile b/drivers/vhost/Makefile
index 6c6df24f770c..ad9c0f8c6d8c 100644
--- a/drivers/vhost/Makefile
+++ b/drivers/vhost/Makefile
@@ -10,4 +10,7 @@ vhost_vsock-y := vsock.o
 
 obj-$(CONFIG_VHOST_RING) += vringh.o
 
+obj-$(CONFIG_VHOST_MDEV) += vhost_mdev.o
+vhost_mdev-y := mdev.o
+
 obj-$(CONFIG_VHOST)	+= vhost.o
diff --git a/drivers/vhost/mdev.c b/drivers/vhost/mdev.c
new file mode 100644
index 000000000000..236cd6eedaad
--- /dev/null
+++ b/drivers/vhost/mdev.c
@@ -0,0 +1,556 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Vhost driver for mediated device based backends.
+ *
+ * Copyright (C) 2018-2019 Intel Corporation.
+ *
+ * Author: Tiwei Bie <tiwei.bie@intel.com>
+ *
+ * Thanks to Jason Wang and Michael S. Tsirkin for the valuable
+ * comments and suggestions.  And thanks to Cunming Liang and
+ * Zhihong Wang for all their supports.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mdev.h>
+#include <linux/vfio.h>
+#include <linux/vhost.h>
+#include <linux/virtio_net.h>
+#include <linux/virtio_mdev_ops.h>
+#include <linux/nospec.h>
+
+#include "vhost.h"
+
+enum {
+	VHOST_MDEV_FEATURES =
+		(1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) |
+		(1ULL << VIRTIO_F_ANY_LAYOUT) |
+		(1ULL << VIRTIO_F_VERSION_1) |
+		(1ULL << VIRTIO_F_IOMMU_PLATFORM) |
+		(1ULL << VIRTIO_F_RING_PACKED) |
+		(1ULL << VIRTIO_F_ORDER_PLATFORM) |
+		(1ULL << VIRTIO_RING_F_INDIRECT_DESC) |
+		(1ULL << VIRTIO_RING_F_EVENT_IDX),
+
+	VHOST_MDEV_NET_FEATURES = VHOST_MDEV_FEATURES |
+		(1ULL << VIRTIO_NET_F_CSUM) |
+		(1ULL << VIRTIO_NET_F_GUEST_CSUM) |
+		(1ULL << VIRTIO_NET_F_MTU) |
+		(1ULL << VIRTIO_NET_F_MAC) |
+		(1ULL << VIRTIO_NET_F_GUEST_TSO4) |
+		(1ULL << VIRTIO_NET_F_GUEST_TSO6) |
+		(1ULL << VIRTIO_NET_F_GUEST_ECN) |
+		(1ULL << VIRTIO_NET_F_GUEST_UFO) |
+		(1ULL << VIRTIO_NET_F_HOST_TSO4) |
+		(1ULL << VIRTIO_NET_F_HOST_TSO6) |
+		(1ULL << VIRTIO_NET_F_HOST_ECN) |
+		(1ULL << VIRTIO_NET_F_HOST_UFO) |
+		(1ULL << VIRTIO_NET_F_MRG_RXBUF) |
+		(1ULL << VIRTIO_NET_F_STATUS) |
+		(1ULL << VIRTIO_NET_F_SPEED_DUPLEX),
+};
+
+/* Currently, only network backend w/o multiqueue is supported. */
+#define VHOST_MDEV_VQ_MAX	2
+
+struct vhost_mdev {
+	/* The lock is to protect this structure. */
+	struct mutex mutex;
+	struct vhost_dev dev;
+	struct vhost_virtqueue *vqs;
+	int nvqs;
+	int virtio_id;
+	bool opened;
+	struct mdev_device *mdev;
+};
+
+static const u64 vhost_mdev_features[] = {
+	[VIRTIO_ID_NET] = VHOST_MDEV_NET_FEATURES,
+};
+
+static void handle_vq_kick(struct vhost_work *work)
+{
+	struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
+						  poll.work);
+	struct vhost_mdev *m = container_of(vq->dev, struct vhost_mdev, dev);
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(m->mdev);
+
+	ops->kick_vq(m->mdev, vq - m->vqs);
+}
+
+static irqreturn_t vhost_mdev_virtqueue_cb(void *private)
+{
+	struct vhost_virtqueue *vq = private;
+	struct eventfd_ctx *call_ctx = vq->call_ctx;
+
+	if (call_ctx)
+		eventfd_signal(call_ctx, 1);
+
+	return IRQ_HANDLED;
+}
+
+static void vhost_mdev_reset(struct vhost_mdev *m)
+{
+	struct mdev_device *mdev = m->mdev;
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+
+	ops->set_status(mdev, 0);
+}
+
+static long vhost_mdev_get_device_id(struct vhost_mdev *m, u8 __user *argp)
+{
+	struct mdev_device *mdev = m->mdev;
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+	u32 device_id;
+
+	device_id = ops->get_device_id(mdev);
+
+	if (copy_to_user(argp, &device_id, sizeof(device_id)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static long vhost_mdev_get_status(struct vhost_mdev *m, u8 __user *statusp)
+{
+	struct mdev_device *mdev = m->mdev;
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+	u8 status;
+
+	status = ops->get_status(mdev);
+
+	if (copy_to_user(statusp, &status, sizeof(status)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static long vhost_mdev_set_status(struct vhost_mdev *m, u8 __user *statusp)
+{
+	struct mdev_device *mdev = m->mdev;
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+	u8 status;
+
+	if (copy_from_user(&status, statusp, sizeof(status)))
+		return -EFAULT;
+
+	/*
+	 * Userspace shouldn't remove status bits unless reset the
+	 * status to 0.
+	 */
+	if (status != 0 && (ops->get_status(mdev) & ~status) != 0)
+		return -EINVAL;
+
+	ops->set_status(mdev, status);
+
+	return 0;
+}
+
+static int vhost_mdev_config_validate(struct vhost_mdev *m,
+				      struct vhost_mdev_config *c)
+{
+	long size = 0;
+
+	switch (m->virtio_id) {
+	case VIRTIO_ID_NET:
+		size = sizeof(struct virtio_net_config);
+		break;
+	}
+
+	if (c->len == 0)
+		return -EINVAL;
+
+	if (c->off >= size || c->len > size || c->off + c->len > size)
+		return -E2BIG;
+
+	return 0;
+}
+
+static long vhost_mdev_get_config(struct vhost_mdev *m,
+				  struct vhost_mdev_config __user *c)
+{
+	struct mdev_device *mdev = m->mdev;
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+	struct vhost_mdev_config config;
+	unsigned long size = offsetof(struct vhost_mdev_config, buf);
+	u8 *buf;
+
+	if (copy_from_user(&config, c, size))
+		return -EFAULT;
+	if (vhost_mdev_config_validate(m, &config))
+		return -EINVAL;
+	buf = kvzalloc(config.len, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	ops->get_config(mdev, config.off, buf, config.len);
+
+	if (copy_to_user(c->buf, buf, config.len)) {
+		kvfree(buf);
+		return -EFAULT;
+	}
+
+	kvfree(buf);
+	return 0;
+}
+
+static long vhost_mdev_set_config(struct vhost_mdev *m,
+				  struct vhost_mdev_config __user *c)
+{
+	struct mdev_device *mdev = m->mdev;
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+	struct vhost_mdev_config config;
+	unsigned long size = offsetof(struct vhost_mdev_config, buf);
+	u8 *buf;
+
+	if (copy_from_user(&config, c, size))
+		return -EFAULT;
+	if (vhost_mdev_config_validate(m, &config))
+		return -EINVAL;
+	buf = kvzalloc(config.len, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	if (copy_from_user(buf, c->buf, config.len)) {
+		kvfree(buf);
+		return -EFAULT;
+	}
+
+	ops->set_config(mdev, config.off, buf, config.len);
+
+	kvfree(buf);
+	return 0;
+}
+
+static long vhost_mdev_get_features(struct vhost_mdev *m, u64 __user *featurep)
+{
+	struct mdev_device *mdev = m->mdev;
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+	u64 features;
+
+	features = ops->get_features(mdev);
+	features &= vhost_mdev_features[m->virtio_id];
+
+	if (copy_to_user(featurep, &features, sizeof(features)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static long vhost_mdev_set_features(struct vhost_mdev *m, u64 __user *featurep)
+{
+	struct mdev_device *mdev = m->mdev;
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+	u64 features;
+
+	/*
+	 * It's not allowed to change the features after they have
+	 * been negotiated.
+	 */
+	if (ops->get_status(mdev) & VIRTIO_CONFIG_S_FEATURES_OK)
+		return -EBUSY;
+
+	if (copy_from_user(&features, featurep, sizeof(features)))
+		return -EFAULT;
+
+	if (features & ~vhost_mdev_features[m->virtio_id])
+		return -EINVAL;
+
+	if (ops->set_features(mdev, features))
+		return -EINVAL;
+
+	return 0;
+}
+
+static long vhost_mdev_get_vring_num(struct vhost_mdev *m, u16 __user *argp)
+{
+	struct mdev_device *mdev = m->mdev;
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+	u16 num;
+
+	num = ops->get_vq_num_max(mdev);
+
+	if (copy_to_user(argp, &num, sizeof(num)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static long vhost_mdev_vring_ioctl(struct vhost_mdev *m, unsigned int cmd,
+				   void __user *argp)
+{
+	struct mdev_device *mdev = m->mdev;
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+	struct virtio_mdev_callback cb;
+	struct vhost_virtqueue *vq;
+	struct vhost_vring_state s;
+	u8 status;
+	u32 idx;
+	long r;
+
+	r = get_user(idx, (u32 __user *)argp);
+	if (r < 0)
+		return r;
+	if (idx >= m->nvqs)
+		return -ENOBUFS;
+
+	idx = array_index_nospec(idx, m->nvqs);
+	vq = &m->vqs[idx];
+
+	status = ops->get_status(mdev);
+
+	/*
+	 * It's not allowed to detect and program vqs before
+	 * features negotiation or after enabling driver.
+	 */
+	if (!(status & VIRTIO_CONFIG_S_FEATURES_OK) ||
+	    (status & VIRTIO_CONFIG_S_DRIVER_OK))
+		return -EBUSY;
+
+	if (cmd == VHOST_MDEV_SET_VRING_ENABLE) {
+		if (copy_from_user(&s, argp, sizeof(s)))
+			return -EFAULT;
+		ops->set_vq_ready(mdev, idx, s.num);
+		return 0;
+	}
+
+	/*
+	 * It's not allowed to detect and program vqs with
+	 * vqs enabled.
+	 */
+	if (ops->get_vq_ready(mdev, idx))
+		return -EBUSY;
+
+	if (cmd == VHOST_GET_VRING_BASE)
+		vq->last_avail_idx = ops->get_vq_state(m->mdev, idx);
+
+	r = vhost_vring_ioctl(&m->dev, cmd, argp);
+	if (r)
+		return r;
+
+	switch (cmd) {
+	case VHOST_SET_VRING_ADDR:
+		/*
+		 * In vhost-mdev, the ring addresses set by userspace should
+		 * be the DMA addresses within the VFIO container/group.
+		 */
+		if (ops->set_vq_address(mdev, idx, (u64)vq->desc,
+					(u64)vq->avail, (u64)vq->used))
+			r = -EINVAL;
+		break;
+
+	case VHOST_SET_VRING_BASE:
+		if (ops->set_vq_state(mdev, idx, vq->last_avail_idx))
+			r = -EINVAL;
+		break;
+
+	case VHOST_SET_VRING_CALL:
+		if (vq->call_ctx) {
+			cb.callback = vhost_mdev_virtqueue_cb;
+			cb.private = vq;
+		} else {
+			cb.callback = NULL;
+			cb.private = NULL;
+		}
+		ops->set_vq_cb(mdev, idx, &cb);
+		break;
+
+	case VHOST_SET_VRING_NUM:
+		ops->set_vq_num(mdev, idx, vq->num);
+		break;
+	}
+
+	return r;
+}
+
+static int vhost_mdev_open(void *device_data)
+{
+	struct vhost_mdev *m = device_data;
+	struct vhost_dev *dev;
+	struct vhost_virtqueue **vqs;
+	int nvqs, i, r;
+
+	if (!try_module_get(THIS_MODULE))
+		return -ENODEV;
+
+	mutex_lock(&m->mutex);
+
+	if (m->opened) {
+		r = -EBUSY;
+		goto err;
+	}
+
+	nvqs = m->nvqs;
+	vhost_mdev_reset(m);
+
+	vqs = kmalloc_array(nvqs, sizeof(*vqs), GFP_KERNEL);
+	if (!vqs) {
+		r = -ENOMEM;
+		goto err;
+	}
+
+	dev = &m->dev;
+	for (i = 0; i < nvqs; i++) {
+		vqs[i] = &m->vqs[i];
+		vqs[i]->handle_kick = handle_vq_kick;
+	}
+	vhost_dev_init(dev, vqs, nvqs, 0, 0, 0);
+	m->opened = true;
+	mutex_unlock(&m->mutex);
+
+	return 0;
+
+err:
+	mutex_unlock(&m->mutex);
+	module_put(THIS_MODULE);
+	return r;
+}
+
+static void vhost_mdev_release(void *device_data)
+{
+	struct vhost_mdev *m = device_data;
+
+	mutex_lock(&m->mutex);
+	vhost_mdev_reset(m);
+	vhost_dev_stop(&m->dev);
+	vhost_dev_cleanup(&m->dev);
+
+	kfree(m->dev.vqs);
+	m->opened = false;
+	mutex_unlock(&m->mutex);
+	module_put(THIS_MODULE);
+}
+
+static long vhost_mdev_unlocked_ioctl(void *device_data,
+				      unsigned int cmd, unsigned long arg)
+{
+	struct vhost_mdev *m = device_data;
+	void __user *argp = (void __user *)arg;
+	long r;
+
+	mutex_lock(&m->mutex);
+
+	switch (cmd) {
+	case VHOST_MDEV_GET_DEVICE_ID:
+		r = vhost_mdev_get_device_id(m, argp);
+		break;
+	case VHOST_MDEV_GET_STATUS:
+		r = vhost_mdev_get_status(m, argp);
+		break;
+	case VHOST_MDEV_SET_STATUS:
+		r = vhost_mdev_set_status(m, argp);
+		break;
+	case VHOST_MDEV_GET_CONFIG:
+		r = vhost_mdev_get_config(m, argp);
+		break;
+	case VHOST_MDEV_SET_CONFIG:
+		r = vhost_mdev_set_config(m, argp);
+		break;
+	case VHOST_GET_FEATURES:
+		r = vhost_mdev_get_features(m, argp);
+		break;
+	case VHOST_SET_FEATURES:
+		r = vhost_mdev_set_features(m, argp);
+		break;
+	case VHOST_MDEV_GET_VRING_NUM:
+		r = vhost_mdev_get_vring_num(m, argp);
+		break;
+	default:
+		/*
+		 * VHOST_SET_MEM_TABLE, VHOST_SET_LOG_BASE, and
+		 * VHOST_SET_LOG_FD are not used yet.
+		 */
+		r = vhost_dev_ioctl(&m->dev, cmd, argp);
+		if (r == -ENOIOCTLCMD)
+			r = vhost_mdev_vring_ioctl(m, cmd, argp);
+	}
+
+	mutex_unlock(&m->mutex);
+	return r;
+}
+
+static const struct vfio_device_ops vfio_vhost_mdev_dev_ops = {
+	.name		= "vfio-vhost-mdev",
+	.open		= vhost_mdev_open,
+	.release	= vhost_mdev_release,
+	.ioctl		= vhost_mdev_unlocked_ioctl,
+};
+
+static int vhost_mdev_probe(struct device *dev)
+{
+	struct mdev_device *mdev = mdev_from_dev(dev);
+	const struct virtio_mdev_device_ops *ops = mdev_get_vhost_ops(mdev);
+	struct vhost_mdev *m;
+	int nvqs, r;
+
+	/* Currently, we only accept the network devices. */
+	if (ops->get_device_id(mdev) != VIRTIO_ID_NET)
+		return -ENOTSUPP;
+
+	if (ops->get_mdev_features(mdev) != VIRTIO_MDEV_F_VERSION_1)
+		return -ENOTSUPP;
+
+	m = devm_kzalloc(dev, sizeof(*m), GFP_KERNEL | __GFP_RETRY_MAYFAIL);
+	if (!m)
+		return -ENOMEM;
+
+	nvqs = VHOST_MDEV_VQ_MAX;
+
+	m->vqs = devm_kmalloc_array(dev, nvqs, sizeof(struct vhost_virtqueue),
+				    GFP_KERNEL);
+	if (!m->vqs)
+		return -ENOMEM;
+
+	mutex_init(&m->mutex);
+
+	m->mdev = mdev;
+	m->nvqs = nvqs;
+	m->virtio_id = ops->get_device_id(mdev);
+
+	r = vfio_add_group_dev(dev, &vfio_vhost_mdev_dev_ops, m);
+	if (r) {
+		mutex_destroy(&m->mutex);
+		return r;
+	}
+
+	return 0;
+}
+
+static void vhost_mdev_remove(struct device *dev)
+{
+	struct vhost_mdev *m;
+
+	m = vfio_del_group_dev(dev);
+	mutex_destroy(&m->mutex);
+}
+
+static const struct mdev_class_id vhost_mdev_match[] = {
+	{ MDEV_CLASS_ID_VHOST },
+	{ 0 },
+};
+MODULE_DEVICE_TABLE(mdev, vhost_mdev_match);
+
+static struct mdev_driver vhost_mdev_driver = {
+	.name	= "vhost_mdev",
+	.probe	= vhost_mdev_probe,
+	.remove	= vhost_mdev_remove,
+	.id_table = vhost_mdev_match,
+};
+
+static int __init vhost_mdev_init(void)
+{
+	return mdev_register_driver(&vhost_mdev_driver, THIS_MODULE);
+}
+module_init(vhost_mdev_init);
+
+static void __exit vhost_mdev_exit(void)
+{
+	mdev_unregister_driver(&vhost_mdev_driver);
+}
+module_exit(vhost_mdev_exit);
+
+MODULE_VERSION("0.0.1");
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Intel Corporation");
+MODULE_DESCRIPTION("Mediated device based accelerator for virtio");
diff --git a/include/linux/mdev.h b/include/linux/mdev.h
index 9b69b0bbebfd..3e1e03926355 100644
--- a/include/linux/mdev.h
+++ b/include/linux/mdev.h
@@ -117,6 +117,10 @@ void mdev_set_virtio_ops(struct mdev_device *mdev,
 			 const struct virtio_mdev_device_ops *virtio_ops);
 const struct virtio_mdev_device_ops *
 mdev_get_virtio_ops(struct mdev_device *mdev);
+void mdev_set_vhost_ops(struct mdev_device *mdev,
+			const struct virtio_mdev_device_ops *vhost_ops);
+const struct virtio_mdev_device_ops *
+mdev_get_vhost_ops(struct mdev_device *mdev);
 
 extern struct bus_type mdev_bus_type;
 
@@ -133,6 +137,7 @@ struct mdev_device *mdev_from_dev(struct device *dev);
 enum {
 	MDEV_CLASS_ID_VFIO = 1,
 	MDEV_CLASS_ID_VIRTIO = 2,
+	MDEV_CLASS_ID_VHOST = 3,
 	/* New entries must be added here */
 };
 
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index 40d028eed645..061a2824a1b3 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -116,4 +116,22 @@
 #define VHOST_VSOCK_SET_GUEST_CID	_IOW(VHOST_VIRTIO, 0x60, __u64)
 #define VHOST_VSOCK_SET_RUNNING		_IOW(VHOST_VIRTIO, 0x61, int)
 
+/* VHOST_MDEV specific defines */
+
+/* Get the device id. The device ids follow the same definition of
+ * the device id defined in virtio-spec. */
+#define VHOST_MDEV_GET_DEVICE_ID	_IOR(VHOST_VIRTIO, 0x70, __u32)
+/* Get and set the status. The status bits follow the same definition
+ * of the device status defined in virtio-spec. */
+#define VHOST_MDEV_GET_STATUS		_IOR(VHOST_VIRTIO, 0x71, __u8)
+#define VHOST_MDEV_SET_STATUS		_IOW(VHOST_VIRTIO, 0x72, __u8)
+/* Get and set the device config. The device config follows the same
+ * definition of the device config defined in virtio-spec. */
+#define VHOST_MDEV_GET_CONFIG		_IOR(VHOST_VIRTIO, 0x73, struct vhost_mdev_config)
+#define VHOST_MDEV_SET_CONFIG		_IOW(VHOST_VIRTIO, 0x74, struct vhost_mdev_config)
+/* Enable/disable the ring. */
+#define VHOST_MDEV_SET_VRING_ENABLE	_IOW(VHOST_VIRTIO, 0x75, struct vhost_vring_state)
+/* Get the max ring size. */
+#define VHOST_MDEV_GET_VRING_NUM	_IOR(VHOST_VIRTIO, 0x76, __u16)
+
 #endif
diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
index c907290ff065..7b105d0b2fb9 100644
--- a/include/uapi/linux/vhost_types.h
+++ b/include/uapi/linux/vhost_types.h
@@ -119,6 +119,14 @@ struct vhost_scsi_target {
 	unsigned short reserved;
 };
 
+/* VHOST_MDEV specific definitions */
+
+struct vhost_mdev_config {
+	__u32 off;
+	__u32 len;
+	__u8 buf[0];
+};
+
 /* Feature bits */
 /* Log all write descriptors. Can be changed while device is active. */
 #define VHOST_F_LOG_ALL 26
-- 
2.23.0