linux-kernel - Re: [PATCH v4] vhost: introduce mdev based hardware backend

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Date:   Fri, 1 Nov 2019 15:17:39 +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 v4] vhost: introduce mdev based hardware backend


On 2019/10/31 下午10:01, 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/2019/10/30/62
>
> 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;


Any reason why virtio_ops is not used for vhost here?

Other looks good.

Thanks