[virtio-dev] Re: [virtio-comment] Re: [PATCH 09/11] transport-pci: Describe PCI MMR dev config registers

Michael S. Tsirkin
2023-04-14T06:58:44Z

On Fri, Apr 14, 2023 at 10:36:52AM +0800, Jason Wang wrote:
> On Fri, Apr 14, 2023 at 5:08 AM Parav Pandit <parav@nvidia.com> wrote:
> >
> >
> >
> > > From: Michael S. Tsirkin <mst@redhat.com>
> > > Sent: Thursday, April 13, 2023 5:02 PM
> >
> > > This thing ... you move some code to the card and reduce the amount of virtio
> > > knowledge in software but do not eliminate it completely.
> > Sure. Practically there is no knowledge other than transporting like a vxlan encapsulating, here its AQ.
> >
> > > Seems kind of pointless. Minimal hardware changes make more sense to me, I'd
> > > say. Talking about that, what is a minimal hardware change to allow a vdpa
> > > based solution?
> > > I think that's VIRTIO_NET_F_LEGACY_HEADER, right?
>
> I think it is. It would be much easier if we do this.

It does not look like Parav is interested in this approach but
if you like it feel free to propose it.

> >
> > The main requirement/point is that there is virito PCI VF that to be mapped to the guest VM.
> > Hence, there is no vdpa type of hypervisor layer exists in this use case.
>
> It's about mediation which is a must for things like legacy. If
> there's a way that helps the vendor to get rid of the tricky legacy
> completely, then why not?
>
> >
> > This same VF need to be transitional as the guest kernel may not be known.
> > hence sometimes vdpa sometime regular 1.x VF is not an option.
> > Hence for next few years, transitional VF will be plugged in into the guest VM when user is using the PCI VF devices.
>
> I'm not sure I get this. With VIRTIO_NET_F_LEGACY_HEADER, we don't
> need mediation for datapath. For the control path, mediation is a must
> for legacy and it's very easy to keep it work for modern, what's wrong
> with that?
>
> Thanks
>
> >
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> > OASIS Virtual I/O Device (VIRTIO) TC.
> >
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