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

From: Jason Wang
Date: Thu Jul 04 2019 - 00:32:21 EST

On 2019/7/3 äå9:08, Tiwei Bie wrote:
On Wed, Jul 03, 2019 at 08:16:23PM +0800, Jason Wang wrote:
On 2019/7/3 äå7:52, Tiwei Bie wrote:
On Wed, Jul 03, 2019 at 06:09:51PM +0800, Jason Wang wrote:
On 2019/7/3 äå5:13, Tiwei Bie wrote:
Details about this can be found here:

What's new in this version

A new VFIO device type is introduced - vfio-vhost. This addressed
some comments from here:

Below is the updated device interface:

Currently, there are two regions of this device: 1) CONFIG_REGION
(VFIO_VHOST_CONFIG_REGION_INDEX), which can be used to setup the
can be used to notify the device.


The region described by CONFIG_REGION is the main control interface.
Messages will be written to or read from this region.

The message type is determined by the `request` field in message
header. The message size is encoded in the message header too.
The message format looks like this:

struct vhost_vfio_op {
__u64 request;
__u32 flags;
/* Flag values: */
#define VHOST_VFIO_NEED_REPLY 0x1 /* Whether need reply */
__u32 size;
union {
__u64 u64;
struct vhost_vring_state state;
struct vhost_vring_addr addr;
} payload;

The existing vhost-kernel ioctl cmds are reused as the message
requests in above structure.
Still a comments like V1. What's the advantage of inventing a new protocol?
I'm trying to make it work in VFIO's way..

I believe either of the following should be better:

- using vhost ioctl, we can start from SET_VRING_KICK/SET_VRING_CALL and
extend it with e.g notify region. The advantages is that all exist userspace
program could be reused without modification (or minimal modification). And
vhost API hides lots of details that is not necessary to be understood by
application (e.g in the case of container).
Do you mean reusing vhost's ioctl on VFIO device fd directly,
or introducing another mdev driver (i.e. vhost_mdev instead of
using the existing vfio_mdev) for mdev device?
Can we simply add them into ioctl of mdev_parent_ops?
Right, either way, these ioctls have to be and just need to be
added in the ioctl of the mdev_parent_ops. But another thing we
also need to consider is that which file descriptor the userspace
will do the ioctl() on. So I'm wondering do you mean let the
userspace do the ioctl() on the VFIO device fd of the mdev

Yes. Is there any other way btw?