Date:   Tue, 22 Oct 2019 21:30:16 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Tiwei Bie <tiwei.bie@...el.com>, mst@...hat.com,
        alex.williamson@...hat.com, maxime.coquelin@...hat.com
Cc:     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 v2] vhost: introduce mdev based hardware backend


On 2019/10/22 下午5:52, 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.
>
> Signed-off-by: Tiwei Bie <tiwei.bie@...el.com>
> ---
> This patch depends on below series:
> https://lkml.org/lkml/2019/10/17/286
>
> 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;


Any idea on how to extend it to support devices other than net? I think 
we want a generic API or an API that could be made generic in the future.

Do we want to e.g having a generic vhost mdev for all kinds of devices 
or introducing e.g vhost-net-mdev and vhost-scsi-mdev?


> - 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 |  12 +
>   drivers/vhost/Kconfig         |   9 +
>   drivers/vhost/Makefile        |   3 +
>   drivers/vhost/mdev.c          | 415 ++++++++++++++++++++++++++++++++++
>   include/linux/mdev.h          |   3 +
>   include/uapi/linux/vhost.h    |  13 ++
>   6 files changed, 455 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 5834f6b7c7a5..2963f65e6648 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -69,6 +69,18 @@ void mdev_set_virtio_ops(struct mdev_device *mdev,
>   }
>   EXPORT_SYMBOL(mdev_set_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)
> +{
> +	WARN_ON(mdev->class_id);
> +	mdev->class_id = MDEV_CLASS_ID_VHOST;
> +	mdev->device_ops = vhost_ops;
> +}
> +EXPORT_SYMBOL(mdev_set_vhost_ops);
> +
>   const void *mdev_get_dev_ops(struct mdev_device *mdev)
>   {
>   	return mdev->device_ops;
> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> index 3d03ccbd1adc..7b5c2f655af7 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 "Vhost driver for Mediated devices"
> +	depends on EVENTFD && VFIO && VFIO_MDEV
> +	select VHOST
> +	default n
> +	---help---
> +	Say M here to enable the vhost_mdev module for use with
> +	the mediated device based 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..5f9cae61018c
> --- /dev/null
> +++ b/drivers/vhost/mdev.c
> @@ -0,0 +1,415 @@
> +// 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 <linux/virtio_ids.h>
> +
> +#include "vhost.h"
> +
> +/* 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;
> +	u64 status;
> +	u64 features;
> +	u64 acked_features;
> +	bool opened;
> +	struct mdev_device *mdev;
> +};
> +
> +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_dev_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_dev_ops(mdev);
> +
> +	m->status = 0;
> +	return ops->set_status(mdev, m->status);
> +}
> +
> +static long vhost_mdev_get_status(struct vhost_mdev *m, u8 __user *statusp)
> +{
> +	const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(m->mdev);
> +	struct mdev_device *mdev = m->mdev;
> +	u8 status;
> +
> +	status = ops->get_status(mdev);
> +	m->status = status;
> +
> +	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)
> +{
> +	const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(m->mdev);
> +	struct mdev_device *mdev = m->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 && (m->status & ~status) != 0)
> +		return -EINVAL;


We don't cache vq ready information but we cache status and features 
here, any reason for this?


> +
> +	ops->set_status(mdev, status);
> +	m->status = ops->get_status(mdev);
> +
> +	return 0;
> +}
> +
> +static long vhost_mdev_get_features(struct vhost_mdev *m, u64 __user *featurep)
> +{
> +	if (copy_to_user(featurep, &m->features, sizeof(m->features)))
> +		return -EFAULT;


As discussed in previous version do we need to filter out MQ feature here?


> +	return 0;
> +}
> +
> +static long vhost_mdev_set_features(struct vhost_mdev *m, u64 __user *featurep)
> +{
> +	const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(m->mdev);
> +	struct mdev_device *mdev = m->mdev;
> +	u64 features;
> +
> +	/*
> +	 * It's not allowed to change the features after they have
> +	 * been negotiated.
> +	 */
> +	if (m->status & VIRTIO_CONFIG_S_FEATURES_OK)
> +		return -EPERM;


-EBUSY?


> +
> +	if (copy_from_user(&features, featurep, sizeof(features)))
> +		return -EFAULT;
> +
> +	if (features & ~m->features)
> +		return -EINVAL;
> +
> +	m->acked_features = features;
> +	if (ops->set_features(mdev, m->acked_features))
> +		return -ENODEV;


-EINVAL should be better, this would be more obvious for parent that 
wants to force any feature.


> +
> +	return 0;
> +}
> +
> +static long vhost_mdev_get_vring_num(struct vhost_mdev *m, u16 __user *argp)
> +{
> +	const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(m->mdev);
> +	struct mdev_device *mdev = m->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_get_queue_num(struct vhost_mdev *m, u32 __user *argp)
> +{
> +	u32 nvqs = m->nvqs;
> +
> +	if (copy_to_user(argp, &nvqs, sizeof(nvqs)))
> +		return -EFAULT;
> +	return 0;
> +}
> +
> +static long vhost_mdev_vring_ioctl(struct vhost_mdev *m, unsigned int cmd,
> +				   void __user *argp)
> +{
> +	const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(m->mdev);
> +	struct mdev_device *mdev = m->mdev;
> +	struct virtio_mdev_callback cb;
> +	struct vhost_virtqueue *vq;
> +	struct vhost_vring_state s;
> +	u32 idx;
> +	long r;
> +
> +	r = get_user(idx, (u32 __user *)argp);
> +	if (r < 0)
> +		return r;
> +	if (idx >= m->nvqs)
> +		return -ENOBUFS;
> +
> +	/*
> +	 * It's not allowed to detect and program vqs before
> +	 * features negotiation or after enabling driver.
> +	 */
> +	if (!(m->status & VIRTIO_CONFIG_S_FEATURES_OK) ||
> +	    (m->status & VIRTIO_CONFIG_S_DRIVER_OK))
> +		return -EPERM;


So the question is: is it better to do this in parent or not?


> +
> +	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 -EPERM;
> +
> +	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;
> +		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);
> +
> +	memset(&m->dev, 0, sizeof(m->dev));
> +	memset(m->vqs, 0, nvqs * sizeof(struct vhost_virtqueue));
> +
> +	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_STATUS:
> +		r = vhost_mdev_get_status(m, argp);
> +		break;
> +	case VHOST_MDEV_SET_STATUS:
> +		r = vhost_mdev_set_status(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;
> +	case VHOST_MDEV_GET_QUEUE_NUM:
> +		r = vhost_mdev_get_queue_num(m, argp);
> +		break;


It's not clear to me that how this API will be used by userspace? I 
think e.g features without MQ implies the queue num here.


> +	default:
> +		r = vhost_dev_ioctl(&m->dev, cmd, argp);


I believe having SET_MEM_TABLE/SET_LOG_BASE/SET_LOG_FD  is for future 
support of those features. If it's true need add some comments on this.


> +		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_dev_ops(mdev);
> +	struct vhost_mdev *m;
> +	int nvqs, r;
> +
> +	/* Currently, only network backend is supported. */
> +	if (ops->get_device_id(mdev) != VIRTIO_ID_NET)
> +		return -ENOTSUPP;


If we decide to go with the way of vhost-net-mdev, probably need 
something smarter. E.g a vhost bus etc.


> +
> +	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->nvqs = nvqs;
> +
> +	m->vqs = devm_kmalloc_array(dev, nvqs, sizeof(struct vhost_virtqueue),
> +				    GFP_KERNEL);
> +	if (!m->vqs)
> +		return -ENOMEM;


Is it better to move those allocation to open? Otherwise the memset 
there seems strange.


> +
> +	r = vfio_add_group_dev(dev, &vfio_vhost_mdev_dev_ops, m);
> +	if (r)
> +		return r;
> +
> +	mutex_init(&m->mutex);
> +	m->features = ops->get_features(mdev);
> +	m->mdev = mdev;
> +	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_DESCRIPTION("Mediated device based accelerator for virtio");
> diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> index 13e045e09d3b..6060cdbe6d3e 100644
> --- a/include/linux/mdev.h
> +++ b/include/linux/mdev.h
> @@ -114,6 +114,8 @@ void mdev_set_vfio_ops(struct mdev_device *mdev,
>   		       const struct vfio_mdev_device_ops *vfio_ops);
>   void mdev_set_virtio_ops(struct mdev_device *mdev,
>                            const struct virtio_mdev_device_ops *virtio_ops);
> +void mdev_set_vhost_ops(struct mdev_device *mdev,
> +			const struct virtio_mdev_device_ops *vhost_ops);
>   const void *mdev_get_dev_ops(struct mdev_device *mdev);
>   
>   extern struct bus_type mdev_bus_type;
> @@ -131,6 +133,7 @@ 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..dad3c62bd91b 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -116,4 +116,17 @@
>   #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 and set the status of the backend. The status bits follow the
> + * same definition of the device status defined in virtio-spec. */
> +#define VHOST_MDEV_GET_STATUS		_IOW(VHOST_VIRTIO, 0x70, __u8)
> +#define VHOST_MDEV_SET_STATUS		_IOW(VHOST_VIRTIO, 0x71, __u8)
> +/* Enable/disable the ring. */
> +#define VHOST_MDEV_SET_VRING_ENABLE	_IOW(VHOST_VIRTIO, 0x72, struct vhost_vring_state)
> +/* Get the max ring size. */
> +#define VHOST_MDEV_GET_VRING_NUM	_IOW(VHOST_VIRTIO, 0x73, __u16)
> +/* Get the max number of queues. */
> +#define VHOST_MDEV_GET_QUEUE_NUM	_IOW(VHOST_VIRTIO, 0x74, __u32)


Do we need API for userspace to get backend capability? (that calls 
get_mdev_device_features())

Thanks


> +
>   #endif

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