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

[Jason Wang <jasowang@redhat.com>]

On Fri, Apr 14, 2023 at 5:08âAM 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.

>
> 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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