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

Parav Pandit
2023-04-13T21:08:27Z

> 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?

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.

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.