Date:   Wed, 30 Oct 2019 15:07:12 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Tiwei Bie <tiwei.bie@...el.com>
Cc:     mst@...hat.com, alex.williamson@...hat.com,
        maxime.coquelin@...hat.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, dan.daly@...el.com,
        cunming.liang@...el.com, zhihong.wang@...el.com,
        lingshan.zhu@...el.com
Subject: Re: [PATCH v3] vhost: introduce mdev based hardware backend


On 2019/10/30 下午1:52, Tiwei Bie wrote:
> On Wed, Oct 30, 2019 at 09:55:57AM +0800, Jason Wang wrote:
>> On 2019/10/29 下午6:07, Tiwei Bie wrote:
>>> 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.
>>
>> Hi Tiwei:
>>
>> The patch looks good overall, just few comments & nits.
> Thanks for the review! I do appreciate it.


You're welcome :)


>
>>
>>> Signed-off-by: Tiwei Bie <tiwei.bie@...el.com>
>>> ---
>>> This patch depends on below series:
>>> https://lkml.org/lkml/2019/10/23/614
>>>
>>> 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             | 554 +++++++++++++++++++++++++++++++
>>>  include/linux/mdev.h             |   5 +
>>>  include/uapi/linux/vhost.h       |  18 +
>>>  include/uapi/linux/vhost_types.h |   8 +
>>>  8 files changed, 621 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 9b00c3513120..3cfd787d605c 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..35b2fb33e686
>>> --- /dev/null
>>> +++ b/drivers/vhost/mdev.c
>>> @@ -0,0 +1,554 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/*
>>> + * Vhost driver for mediated device based backends.
>>> + *
>>> + * Copyright (C) 2018-2019 Intel Corporation.
>>> + *
>>> + * Author: Tiwei Bie <tiwei.bie@...el.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 "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;
>>> +}
>>
>> I believe we need get_vendor_id() as well?
> Currently, there is no official way for vendors to do vendor
> specific extensions in vhost-mdev yet. It might be better to
> add this ioctl when we support this.


Good point.


>
>>
>>> +
>>> +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;
>>
>> I think it's better to let the parent to do such validation. Especially
>> consider that the size of config may depend on feature (e.g MQ).
> Above check is just a basic sanity check to make sure
> that e.g. we won't alloc a huge amount of memory.


I see.


>
>>
>>> +	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;
>>> +
>>> +	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;
>>> +
>>> +	vq = &m->vqs[idx];
>>> +
>>> +	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 = -ENODEV;
>>
>> Nit: It looks to me that we need expose alignment of vq to userspace
>> (get_vq_align()).
> Guest drivers are using (maybe hardcoded) alignments based
> on the alignment requirements defined in the spec. It might
> be better to let backends follow the same standard for the
> compatibility.


Ok.

Thanks


>
>> Thanks
>>
>>
>>> +		break;
>>> +
>>> +	case VHOST_SET_VRING_BASE:
>>> +		if (ops->set_vq_state(mdev, idx, vq->last_avail_idx))
>>> +			r = -ENODEV;
>>> +		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

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