[RFC v4 3/3] vhost: introduce mdev based hardware backend

Jason Wang
2019-09-17T07:26:30Z

On 2019/9/17 ??9:02, Tiwei Bie wrote:
> More details about this patch can be found from the cover
> letter for now. Only compile test has been done for now.
>
> Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
> ---
>   drivers/vhost/Kconfig            |   9 +
>   drivers/vhost/Makefile           |   3 +
>   drivers/vhost/mdev.c             | 462 +++++++++++++++++++++++++++++++
>   drivers/vhost/vhost.c            |  39 ++-
>   drivers/vhost/vhost.h            |   6 +
>   include/uapi/linux/vhost.h       |  10 +
>   include/uapi/linux/vhost_types.h |   5 +
>   7 files changed, 528 insertions(+), 6 deletions(-)
>   create mode 100644 drivers/vhost/mdev.c
>
> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> index 3d03ccbd1adc..ef9783156d2e 100644
> --- a/drivers/vhost/Kconfig
> +++ b/drivers/vhost/Kconfig
> @@ -34,6 +34,15 @@ config VHOST_VSOCK
>   	To compile this driver as a module, choose M here: the module will be
called
>   	vhost_vsock.
>
> +config VHOST_MDEV
> +	tristate "Mediated device based hardware vhost accelerator"
> +	depends on EVENTFD && VFIO && VFIO_MDEV
> +	select VHOST
> +	default n
> +	---help---
> +	Say Y here to enable the vhost_mdev module
> +	for use with hardware vhost accelerators
> +
>   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..8c6597aff45e
> --- /dev/null
> +++ b/drivers/vhost/mdev.c
> @@ -0,0 +1,462 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2018-2019 Intel Corporation.
> + */
> +
> +#include <linux/compat.h>
> +#include <linux/kernel.h>
> +#include <linux/miscdevice.h>
> +#include <linux/mdev.h>
> +#include <linux/module.h>
> +#include <linux/vfio.h>
> +#include <linux/vhost.h>
> +#include <linux/virtio_mdev.h>
> +
> +#include "vhost.h"
> +
> +struct vhost_mdev {
> +	struct mutex mutex;
> +	struct vhost_dev dev;
> +	struct vhost_virtqueue *vqs;
> +	int nvqs;
> +	u64 state;
> +	u64 features;
> +	u64 acked_features;
> +	struct vfio_group *vfio_group;
> +	struct vfio_device *vfio_device;
> +	struct mdev_device *mdev;
> +};
> +
> +/*
> + * XXX
> + * We assume virtio_mdev.ko exposes below symbols for now, as we
> + * don't have a proper way to access parent ops directly yet.
> + *
> + * virtio_mdev_readl()
> + * virtio_mdev_writel()
> + */
> +extern u32 virtio_mdev_readl(struct mdev_device *mdev, loff_t off);
> +extern void virtio_mdev_writel(struct mdev_device *mdev, loff_t off, u32
val);


Need to consider a better approach, I feel we should do it through some
kind of mdev driver instead of talk to mdev device directly.


> +
> +static u8 mdev_get_status(struct mdev_device *mdev)
> +{
> +	return virtio_mdev_readl(mdev, VIRTIO_MDEV_STATUS);
> +}
> +
> +static void mdev_set_status(struct mdev_device *mdev, u8 status)
> +{
> +	virtio_mdev_writel(mdev, VIRTIO_MDEV_STATUS, status);
> +}
> +
> +static void mdev_add_status(struct mdev_device *mdev, u8 status)
> +{
> +	status |= mdev_get_status(mdev);
> +	mdev_set_status(mdev, status);
> +}
> +
> +static void mdev_reset(struct mdev_device *mdev)
> +{
> +	mdev_set_status(mdev, 0);
> +}
> +
> +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);
> +
> +	virtio_mdev_writel(m->mdev, VIRTIO_MDEV_QUEUE_NOTIFY, vq - m->vqs);
> +}
> +
> +static long vhost_mdev_start_backend(struct vhost_mdev *m)
> +{
> +	struct mdev_device *mdev = m->mdev;
> +	u64 features = m->acked_features;
> +	u64 addr;
> +	struct vhost_virtqueue *vq;
> +	int queue_id;
> +
> +	features |= 1ULL << VIRTIO_F_IOMMU_PLATFORM;


Is it better to get this feature from backend?


> +
> +	virtio_mdev_writel(mdev, VIRTIO_MDEV_DRIVER_FEATURES_SEL, 1);
> +	virtio_mdev_writel(mdev, VIRTIO_MDEV_DRIVER_FEATURES,
> +			   (u32)(features >> 32));
> +
> +	virtio_mdev_writel(mdev, VIRTIO_MDEV_DRIVER_FEATURES_SEL, 0);
> +	virtio_mdev_writel(mdev, VIRTIO_MDEV_DRIVER_FEATURES,
> +			   (u32)features);
> +
> +	mdev_add_status(mdev, VIRTIO_CONFIG_S_FEATURES_OK);
> +	if (!(mdev_get_status(mdev) & VIRTIO_CONFIG_S_FEATURES_OK))
> +		return -ENODEV;
> +
> +	for (queue_id = 0; queue_id < m->nvqs; queue_id++) {
> +		vq = &m->vqs[queue_id];
> +
> +		if (!vq->desc || !vq->avail || !vq->used)
> +			break;
> +
> +		virtio_mdev_writel(mdev, VIRTIO_MDEV_QUEUE_NUM, vq->num);
> +
> +		if (!vhost_translate_ring_addr(vq, (u64)vq->desc,
> +					       vhost_get_desc_size(vq, vq->num),
> +					       &addr))
> +			return -EINVAL;


Interesting, any reason for doing such kinds of translation to HVA? I
believe the add should already an IOVA that has been map by VFIO.


> +
> +		virtio_mdev_writel(mdev, VIRTIO_MDEV_QUEUE_DESC_LOW, addr);
> +		virtio_mdev_writel(mdev, VIRTIO_MDEV_QUEUE_DESC_HIGH,
> +				   (addr >> 32));
> +
> +		if (!vhost_translate_ring_addr(vq, (u64)vq->avail,
> +					       vhost_get_avail_size(vq, vq->num),
> +					       &addr))
> +			return -EINVAL;
> +
> +		virtio_mdev_writel(mdev, VIRTIO_MDEV_QUEUE_AVAIL_LOW, addr);
> +		virtio_mdev_writel(mdev, VIRTIO_MDEV_QUEUE_AVAIL_HIGH,
> +				   (addr >> 32));
> +
> +		if (!vhost_translate_ring_addr(vq, (u64)vq->used,
> +					       vhost_get_used_size(vq, vq->num),
> +					       &addr))
> +			return -EINVAL;
> +
> +		virtio_mdev_writel(mdev, VIRTIO_MDEV_QUEUE_USED_LOW, addr);
> +		virtio_mdev_writel(mdev, VIRTIO_MDEV_QUEUE_USED_HIGH,
> +				   (addr >> 32));
> +
> +		// XXX: we need to support set_vring_base


I'm working on V2 that support this API.


> +
> +		virtio_mdev_writel(mdev, VIRTIO_MDEV_QUEUE_READY, 1);
> +	}
> +
> +	// XXX: we need to setup interrupt as well


V2 will have a better interrupt API like some kind of callback. It could
be as simple as a wrapper of eventfd_signal().


> +
> +	mdev_add_status(mdev, VIRTIO_CONFIG_S_DRIVER_OK);
> +	return 0;
> +}
> +
> +static long vhost_mdev_stop_backend(struct vhost_mdev *m)
> +{
> +	struct mdev_device *mdev = m->mdev;
> +
> +	mdev_reset(mdev);
> +	mdev_add_status(mdev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
> +	mdev_add_status(mdev, VIRTIO_CONFIG_S_DRIVER);
> +	return 0;
> +}
> +
> +static long vhost_set_state(struct vhost_mdev *m, u64 __user *statep)
> +{
> +	u64 state;
> +	long r;
> +
> +	if (copy_from_user(&state, statep, sizeof(state)))
> +		return -EFAULT;
> +
> +	if (state >= VHOST_MDEV_S_MAX)
> +		return -EINVAL;
> +
> +	if (m->state == state)
> +		return 0;
> +
> +	m->state = state;
> +
> +	switch (m->state) {
> +	case VHOST_MDEV_S_RUNNING:
> +		r = vhost_mdev_start_backend(m);
> +		break;
> +	case VHOST_MDEV_S_STOPPED:
> +		r = vhost_mdev_stop_backend(m);
> +		break;
> +	default:
> +		r = -EINVAL;
> +		break;
> +	}
> +
> +	return r;
> +}
> +
> +static long vhost_get_features(struct vhost_mdev *m, u64 __user *featurep)
> +{
> +	if (copy_to_user(featurep, &m->features, sizeof(m->features)))
> +		return -EFAULT;
> +	return 0;
> +}
> +
> +static long vhost_set_features(struct vhost_mdev *m, u64 __user *featurep)
> +{
> +	u64 features;
> +
> +	if (copy_from_user(&features, featurep, sizeof(features)))
> +		return -EFAULT;
> +
> +	if (features & ~m->features)
> +		return -EINVAL;
> +
> +	m->acked_features = features;
> +
> +	return 0;
> +}
> +
> +static long vhost_get_vring_base(struct vhost_mdev *m, void __user *argp)
> +{
> +	struct vhost_virtqueue *vq;
> +	u32 idx;
> +	long r;
> +
> +	r = get_user(idx, (u32 __user *)argp);
> +	if (r < 0)
> +		return r;
> +	if (idx >= m->nvqs)
> +		return -ENOBUFS;
> +
> +	vq = &m->vqs[idx];
> +
> +	// XXX: we need to support get_vring_base
> +	//vq->last_avail_idx = virtio_mdev_readl(b->mdev, ...);
> +
> +	return vhost_vring_ioctl(&m->dev, VHOST_GET_VRING_BASE, argp);
> +}
> +
> +static void vhost_mdev_release_backend(struct vhost_mdev *m)
> +{
> +	if (!m->mdev)
> +		return;
> +
> +	if (m->state != VHOST_MDEV_S_STOPPED) {
> +		m->state = VHOST_MDEV_S_STOPPED;
> +		vhost_mdev_stop_backend(m);
> +	}
> +
> +	vhost_dev_stop(&m->dev);
> +	vhost_dev_cleanup(&m->dev);
> +
> +	kfree(m->dev.vqs);
> +	kfree(m->vqs);
> +
> +	vfio_device_put(m->vfio_device);
> +	vfio_group_put_external_user(m->vfio_group);
> +
> +	m->mdev = NULL;
> +}
> +
> +static long vhost_mdev_set_backend(struct vhost_mdev *m,
> +				   struct vhost_mdev_backend __user *argp)
> +{
> +	struct vhost_mdev_backend backend;
> +	struct mdev_device *mdev;
> +	struct vhost_dev *dev;
> +	struct vhost_virtqueue **vqs;
> +	struct file *file;
> +	struct vfio_device *device;
> +	struct vfio_group *group;
> +	unsigned long magic;
> +	u64 features;
> +	int i, nvqs;
> +	long r;
> +
> +	vhost_mdev_release_backend(m);
> +
> +	if (copy_from_user(&backend, argp, sizeof(backend))) {
> +		r = -EFAULT;
> +		goto err;
> +	}
> +
> +	file = fget(backend.group_fd);
> +	if (!file) {
> +		r = -EBADF;
> +		goto err;
> +	}
> +
> +	group = vfio_group_get_external_user(file);
> +	fput(file);
> +	if (IS_ERR(group)) {
> +		r = PTR_ERR(group);
> +		goto err;
> +	}
> +
> +	device = vfio_device_get_from_fd(group, backend.device_fd);
> +	if (!IS_ERR(device)) {
> +		r = PTR_ERR(device);
> +		goto err_put_group;
> +	}
> +
> +	if (!vfio_device_ops_match(device, &vfio_mdev_dev_ops)) {
> +		r = -EINVAL;
> +		goto err_put_device;
> +	}


It looks to me that we can avoid to expose vfio_mdev_dev_ops here.


> +
> +	mdev = vfio_device_data(m->vfio_device);
> +
> +	magic = virtio_mdev_readl(mdev, VIRTIO_MDEV_MAGIC_VALUE);
> +	if (magic != ('v' | 'i' << 8 | 'r' <<
16 | 't' << 24)) {
> +		r = -ENODEV;
> +		goto err_put_device;
> +	}
> +
> +	mdev_reset(mdev);
> +	mdev_add_status(mdev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
> +	mdev_add_status(mdev, VIRTIO_CONFIG_S_DRIVER);
> +
> +	virtio_mdev_writel(mdev, VIRTIO_MDEV_DEVICE_FEATURES_SEL, 1);
> +	features = virtio_mdev_readl(mdev, VIRTIO_MDEV_DEVICE_FEATURES);
> +	features <<= 32;
> +
> +	virtio_mdev_writel(mdev, VIRTIO_MDEV_DEVICE_FEATURES_SEL, 0);
> +	features |= virtio_mdev_readl(mdev, VIRTIO_MDEV_DEVICE_FEATURES);
> +
> +	if (!(features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))) {
> +		r = -EINVAL;
> +		goto err_put_device;
> +	}
> +
> +	m->features = features;
> +
> +	nvqs = virtio_mdev_readl(mdev, VIRTIO_MDEV_QUEUE_NUM_MAX);
> +	m->nvqs = nvqs;
> +
> +	m->vqs = kmalloc_array(nvqs, sizeof(struct vhost_virtqueue),
> +			       GFP_KERNEL);
> +	if (!m->vqs) {
> +		r = -ENOMEM;
> +		goto err_put_device;
> +	}
> +
> +	vqs = kmalloc_array(nvqs, sizeof(*vqs), GFP_KERNEL);
> +	if (!vqs) {
> +		r = -ENOMEM;
> +		goto err_free_vqs;
> +	}
> +
> +	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->vfio_group = group;
> +	m->vfio_device = device;
> +	m->mdev = mdev;
> +
> +	return 0;
> +
> +err_free_vqs:
> +	kfree(m->vqs);
> +err_put_device:
> +	vfio_device_put(device);
> +err_put_group:
> +	vfio_group_put_external_user(group);
> +err:
> +	return r;
> +}
> +
> +static int vhost_mdev_open(struct inode *inode, struct file *f)
> +{
> +	struct vhost_mdev *m;
> +
> +	m = kzalloc(sizeof(*m), GFP_KERNEL | __GFP_RETRY_MAYFAIL);
> +	if (!m)
> +		return -ENOMEM;
> +
> +	mutex_init(&m->mutex);
> +	f->private_data = m;
> +
> +	return 0;
> +}
> +
> +static int vhost_mdev_release(struct inode *inode, struct file *f)
> +{
> +	struct vhost_mdev *m = f->private_data;
> +
> +	vhost_mdev_release_backend(m);
> +	mutex_destroy(&m->mutex);
> +	kfree(m);
> +
> +	return 0;
> +}
> +
> +static long vhost_mdev_ioctl(struct file *f, unsigned int cmd,
> +			     unsigned long arg)
> +{
> +	void __user *argp = (void __user *)arg;
> +	struct vhost_mdev *m = f->private_data;
> +	long r;
> +
> +	mutex_lock(&m->mutex);
> +
> +	if (cmd == VHOST_MDEV_SET_BACKEND) {
> +		r = vhost_mdev_set_backend(m, argp);
> +		goto done;
> +	}
> +
> +	if (!m->mdev) {
> +		r = -EINVAL;
> +		goto done;
> +	}
> +
> +	switch (cmd) {
> +	case VHOST_MDEV_SET_STATE:
> +		r = vhost_set_state(m, argp);
> +		break;
> +	case VHOST_GET_FEATURES:
> +		r = vhost_get_features(m, argp);
> +		break;
> +	case VHOST_SET_FEATURES:
> +		r = vhost_set_features(m, argp);
> +		break;
> +	case VHOST_GET_VRING_BASE:
> +		r = vhost_get_vring_base(m, argp);
> +		break;
> +	default:
> +		r = vhost_dev_ioctl(&m->dev, cmd, argp);
> +		if (r == -ENOIOCTLCMD)
> +			r = vhost_vring_ioctl(&m->dev, cmd, argp);
> +	}
> +
> +done:
> +	mutex_lock(&m->mutex);
> +	return r;
> +}
> +
> +#ifdef CONFIG_COMPAT
> +static long vhost_mdev_compat_ioctl(struct file *f, unsigned int ioctl,
> +				    unsigned long arg)
> +{
> +	return vhost_mdev_ioctl(f, ioctl, (unsigned long)compat_ptr(arg));
> +}
> +#endif
> +
> +static const struct file_operations vhost_mdev_fops = {
> +	.owner		= THIS_MODULE,
> +	.release	= vhost_mdev_release,
> +	.unlocked_ioctl	= vhost_mdev_ioctl,
> +#ifdef CONFIG_COMPAT
> +	.compat_ioctl	= vhost_mdev_compat_ioctl,
> +#endif
> +	.open		= vhost_mdev_open,
> +	.llseek		= noop_llseek,
> +};
> +
> +static struct miscdevice vhost_mdev_misc = {
> +	.minor = MISC_DYNAMIC_MINOR,
> +	.name = "vhost-mdev",
> +	.fops = &vhost_mdev_fops,
> +};
> +
> +static int __init vhost_mdev_init(void)
> +{
> +	return misc_register(&vhost_mdev_misc);
> +}
> +module_init(vhost_mdev_init);
> +
> +static void __exit vhost_mdev_exit(void)
> +{
> +	misc_deregister(&vhost_mdev_misc);
> +}
> +module_exit(vhost_mdev_exit);
> +
> +MODULE_VERSION("0.0.0");
> +MODULE_LICENSE("GPL v2");
> +MODULE_DESCRIPTION("Hardware vhost accelerator abstraction");
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 5dc174ac8cac..0f7236a17a56 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -426,8 +426,7 @@ bool vhost_exceeds_weight(struct vhost_virtqueue *vq,
>   }
>   EXPORT_SYMBOL_GPL(vhost_exceeds_weight);
>
> -static size_t vhost_get_avail_size(struct vhost_virtqueue *vq,
> -				   unsigned int num)
> +size_t vhost_get_avail_size(struct vhost_virtqueue *vq, unsigned int num)
>   {
>   	size_t event __maybe_unused >   	       vhost_has_feature(vq,
VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
> @@ -435,9 +434,9 @@ static size_t vhost_get_avail_size(struct
vhost_virtqueue *vq,
>   	return sizeof(*vq->avail) +
>   	       sizeof(*vq->avail->ring) * num + event;
>   }
> +EXPORT_SYMBOL_GPL(vhost_get_avail_size);
>
> -static size_t vhost_get_used_size(struct vhost_virtqueue *vq,
> -				  unsigned int num)
> +size_t vhost_get_used_size(struct vhost_virtqueue *vq, unsigned int num)
>   {
>   	size_t event __maybe_unused >   	       vhost_has_feature(vq,
VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
> @@ -445,12 +444,13 @@ static size_t vhost_get_used_size(struct
vhost_virtqueue *vq,
>   	return sizeof(*vq->used) +
>   	       sizeof(*vq->used->ring) * num + event;
>   }
> +EXPORT_SYMBOL_GPL(vhost_get_used_size);
>
> -static size_t vhost_get_desc_size(struct vhost_virtqueue *vq,
> -				  unsigned int num)
> +size_t vhost_get_desc_size(struct vhost_virtqueue *vq, unsigned int num)
>   {
>   	return sizeof(*vq->desc) * num;
>   }
> +EXPORT_SYMBOL_GPL(vhost_get_desc_size);
>
>   void vhost_dev_init(struct vhost_dev *dev,
>   		    struct vhost_virtqueue **vqs, int nvqs,
> @@ -2617,6 +2617,33 @@ struct vhost_msg_node *vhost_dequeue_msg(struct
vhost_dev *dev,
>   }
>   EXPORT_SYMBOL_GPL(vhost_dequeue_msg);
>
> +bool vhost_translate_ring_addr(struct vhost_virtqueue *vq, u64 ring_addr,
> +			       u64 len, u64 *addr)
> +{
> +	struct vhost_umem *umem = vq->umem;
> +	struct vhost_umem_node *u;
> +
> +	if (vhost_overflow(ring_addr, len))
> +		return false;
> +
> +	if (vq->iotlb) {
> +		/* Ring address is already IOVA */
> +		*addr = ring_addr;
> +		return true;
> +	}
> +
> +	/* Ring address is host virtual address. */
> +	list_for_each_entry(u, &umem->umem_list, link) {
> +		if (u->userspace_addr <= ring_addr &&
> +		    u->userspace_addr + u->size >= ring_addr + len) {
> +			*addr = ring_addr - u->userspace_addr + u->start;
> +			return true;
> +		}
> +	}
> +
> +	return false;
> +}
> +EXPORT_SYMBOL_GPL(vhost_translate_ring_addr);


As we've discussed, this is necessary.


Thanks


>
>   static int __init vhost_init(void)
>   {
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index e9ed2722b633..294a6bcb6adf 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -189,6 +189,12 @@ long vhost_dev_ioctl(struct vhost_dev *, unsigned int
ioctl, void __user *argp);
>   long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void
__user *argp);
>   bool vhost_vq_access_ok(struct vhost_virtqueue *vq);
>   bool vhost_log_access_ok(struct vhost_dev *);
> +bool vhost_translate_ring_addr(struct vhost_virtqueue *vq, u64 ring_addr,
> +			       u64 len, u64 *addr);
> +
> +size_t vhost_get_avail_size(struct vhost_virtqueue *vq, unsigned int num);
> +size_t vhost_get_used_size(struct vhost_virtqueue *vq, unsigned int num);
> +size_t vhost_get_desc_size(struct vhost_virtqueue *vq, unsigned int num);
>
>   int vhost_get_vq_desc(struct vhost_virtqueue *,
>   		      struct iovec iov[], unsigned int iov_count,
> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> index 40d028eed645..7213aedc8506 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -116,4 +116,14 @@
>   #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 */
> +
> +#define VHOST_MDEV_SET_BACKEND	_IOW(VHOST_VIRTIO, 0x70, \
> +					struct vhost_mdev_backend)
> +#define VHOST_MDEV_SET_STATE	_IOW(VHOST_VIRTIO, 0x71, __u64)
> +
> +#define VHOST_MDEV_S_STOPPED	0
> +#define VHOST_MDEV_S_RUNNING	1
> +#define VHOST_MDEV_S_MAX	2
> +
>   #endif
> diff --git a/include/uapi/linux/vhost_types.h
b/include/uapi/linux/vhost_types.h
> index c907290ff065..f06f0dbb7e51 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -119,6 +119,11 @@ struct vhost_scsi_target {
>   	unsigned short reserved;
>   };
>
> +struct vhost_mdev_backend {
> +	int group_fd;
> +	int device_fd;
> +};
> +
>   /* Feature bits */
>   /* Log all write descriptors. Can be changed while device is active. */
>   #define VHOST_F_LOG_ALL 26