linux-kernel - Re: [RFC v2] vhost: introduce mdev based hardware vhost backend

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Message-ID: <20190703123157.2452bf95@x1.home>
Date:   Wed, 3 Jul 2019 12:31:57 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Tiwei Bie <tiwei.bie@...el.com>
Cc:     mst@...hat.com, jasowang@...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
Subject: Re: [RFC v2] vhost: introduce mdev based hardware vhost backend

On Wed,  3 Jul 2019 17:13:39 +0800
Tiwei Bie <tiwei.bie@...el.com> wrote:
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 8f10748dac79..6c5718ab7eeb 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -201,6 +201,7 @@ struct vfio_device_info {
>  #define VFIO_DEVICE_FLAGS_AMBA  (1 << 3)	/* vfio-amba device */
>  #define VFIO_DEVICE_FLAGS_CCW	(1 << 4)	/* vfio-ccw device */
>  #define VFIO_DEVICE_FLAGS_AP	(1 << 5)	/* vfio-ap device */
> +#define VFIO_DEVICE_FLAGS_VHOST	(1 << 6)	/* vfio-vhost device */
>  	__u32	num_regions;	/* Max region index + 1 */
>  	__u32	num_irqs;	/* Max IRQ index + 1 */
>  };
> @@ -217,6 +218,7 @@ struct vfio_device_info {
>  #define VFIO_DEVICE_API_AMBA_STRING		"vfio-amba"
>  #define VFIO_DEVICE_API_CCW_STRING		"vfio-ccw"
>  #define VFIO_DEVICE_API_AP_STRING		"vfio-ap"
> +#define VFIO_DEVICE_API_VHOST_STRING		"vfio-vhost"
>  
>  /**
>   * VFIO_DEVICE_GET_REGION_INFO - _IOWR(VFIO_TYPE, VFIO_BASE + 8,
> @@ -573,6 +575,23 @@ enum {
>  	VFIO_CCW_NUM_IRQS
>  };
>  
> +/*
> + * The vfio-vhost bus driver makes use of the following fixed region and
> + * IRQ index mapping. Unimplemented regions return a size of zero.
> + * Unimplemented IRQ types return a count of zero.
> + */
> +
> +enum {
> +	VFIO_VHOST_CONFIG_REGION_INDEX,
> +	VFIO_VHOST_NOTIFY_REGION_INDEX,
> +	VFIO_VHOST_NUM_REGIONS
> +};
> +
> +enum {
> +	VFIO_VHOST_VQ_IRQ_INDEX,
> +	VFIO_VHOST_NUM_IRQS
> +};
> +

Note that the vfio API has evolved a bit since vfio-pci started this
way, with fixed indexes for pre-defined region types.  We now support
device specific regions which can be identified by a capability within
the REGION_INFO ioctl return data.  This allows a bit more flexibility,
at the cost of complexity, but the infrastructure already exists in
kernel and QEMU to make it relatively easy.  I think we'll have the
same support for interrupts soon too.  If you continue to pursue the
vfio-vhost direction you might want to consider these before committing
to fixed indexes.  Thanks,

Alex