RE: [virtio-comment] [PATCH v1 1/8] admin: Add theory of operation for device migration

[Parav Pandit <parav@nvidia.com>]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Friday, November 17, 2023 3:38 PM
> 
> On Wed, Nov 15, 2023 at 05:39:43PM +0000, Parav Pandit wrote:
> > > >
> > > > Additionally, if hypervisor has put the trap on virtio config, and
> > > > because the memory device already has the interface for virtio
> > > > config,
> > > >
> > > > Hypervisor can directly write/read from the virtual config to the
> > > > member's
> > > config space, without going through the device context, right?
> > >
> > > If it can do it or it can choose to not. I don't see how it is
> > > related to the discussion here.
> > >
> > It is. I donât see a point of hypervisor not using the native interface provided
> by the member device.
> 
> So for example, it seems reasonable to a member supporting both existing pci
> register interface for compatibility and the future DMA based one for scale. In
> such a case, it seems possible that DMA will expose more features than pci. And
> then a hypervisor might decide to use that in preference to pci registers.

We donât find it right to involve owner device for mediating at current scale and to not break TDISP efforts in upcoming time by such design.
And for future scale, having new SIOV interface makes more sense which has its own direct interface to device.

I finally captured all past discussions in form of a FAQ at [1].

[1] https://docs.google.com/document/d/1Iyn-l3Nm0yls3pZaul4lZiVj8x1s73Ed6rOsmn6LfXc/edit?usp=sharing