Re: Move vhost-user SET_STATUS 0 after get vring base?

[Yajun Wu]

On 4/18/2023 11:34 PM, Michael S. Tsirkin wrote:
> On Tue, Apr 18, 2023 at 11:18:11AM -0400, Stefan Hajnoczi wrote:
> > Hi,
> > Cindy's commit ca71db438bdc ("vhost: implement vhost_dev_start method")
> > added SET_STATUS calls to vhost_dev_start() and vhost_dev_stop() for all
> > vhost backends.
> >
> > Eugenio's commit c3716f260bff ("vdpa: move vhost reset after get vring
> > base") deferred the SET_STATUS 0 call in vhost_dev_stop() until after
> > GET_VRING_BASE for vDPA only. In that commit Eugenio said, "A patch to
> > make vhost_user_dev_start more similar to vdpa is desirable, but it can
> > be added on top".
> >
> > I agree and think it's a good idea to keep the vhost backends in sync
> > where possible.
> >
> > vhost-user still has the old behavior where QEMU sends SET_STATUS 0
> > before GET_VRING_BASE. Most existing vhost-user backends don't implement
> > the SET_STATUS message, so I think no one has tripped over this yet.
> >
> > Any thoughts on making vhost-user behave like vDPA here?
> >
> > Stefan
> Wow. Well  SET_STATUS 0 resets the device so yes, I think doing that
> before GET_VRING_BASE will lose a state. Donnu how it does not trip
> up people, indeed the only idea is if people ignore SET_STATUS.
>
>
> --
> MST

For DPDK vhost-user backend SET_STATUS 0 (reset) is ignored.

Yajun