RE: [PATCH 1/2] virtio: introduce selective queue enabling

[Parav Pandit <parav@nvidia.com>]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Tuesday, June 6, 2023 3:20 PM
> >
> > Can you please highlight, current spec normative which indicates that
> > all queues must be enabled before DRIVER_OK and more queues cannot be
> > enabled after DRIVER_OK?
> 
> 
> This one:
> \drivernormative{\subsection}{Device Initialization}{General Initialization And
> Device Operation / Device Initialization}
> 
> it does not say "all queues" if you want to split hairs but I think assuming it's
> safe to enable queues later is dangerous.
> 
Yes, I have read it few times and every time I concluded that:
it does not say that it must be done before DRIVER_OK and cannot be done after DRIVER_OK.

> E.g. vhost user backends tend to assume no new queues appear after
> DRIVER_OK.

This backend implementation can be improved without introducing new bits on the guest side.
Q reset is already a second example that demonstrates that queues will be disabled/enabled after DRIVER_OK.

And for PCI transport, PCI device and driver do not restrict queue_enable access after DRIVER_OK.