Re: [PATCH v1 0/4] virtio-msg transport layer

On Wed, Feb 25, 2026 at 07:53:38AM -0500, Demi Marie Obenour wrote:
> On 2/25/26 02:45, Manivannan Sadhasivam wrote:
> > Hi Bertrand,
> > 
> > On Fri, Feb 20, 2026 at 09:02:12AM +0000, Bertrand Marquis wrote:
> >> Hi Parav,
> 
> (snip)
> 
> >>> How can one implement a transport without defining the basic data transfer semantics?
> >>
> >> We did a lot of experiments and we are feature equivalent to PCI, MMIO or Channel I/O.
> >> If anything is missing, we are more than happy to discuss it and solve the issue.
> >>
> > 
> > I'd love to have this transport over PCI because it addresses the shortcomings
> > of the existing PCI transport which just assumes that every config space access\
> > is trap and emulate.
> 
> Would you mind elaborating on "over PCI"?
> 
> I can see two meanings for this:
> 
> 1. Virtio-msg over a physical PCI bus for heterogeneous multiprocessing
>    environments.
> 
> 2. Virtio-msg over an emulated PCI bus for QEMU, Cloud Hypervisor,
>    and other existing VMMs.
> 
> Which one are you referring to?
> 

Physical PCI bus, that's why I mentioned 'trap and emulate' which only applies
to emulated PCI bus.

> > But that being said, I somewhat agree with Parav that we should define the bus
> > implementations in the spec to avoid fixing the ABI in the implementations. For
> > instance, if we try to use this transport over PCI, we've got questions like:> 
> > 1. How the device should be bind to the virtio-msg-pci bus driver and not with
> > the existing virtio-pci driver? Should it use a new Vendor ID or Sub-IDs?
> > 
> > 2. How the Virtio messages should be transferred? Is it through endpoint config
> > space or through some other means?
> > 
> > 3. How the notification be delivered from the device to the host? Through
> > INT-X/MSI/MSI-X or even polling?
> > 
> > And these are just a few questions that comes to the top of my head. There could
> > be plenty more.
> > 
> > How can we expect all the virtio-msg bus implementations to adhere to the same
> > format so that the interoperability offered by the Virtio spec is guaranteed?
> This really ought to be included in the virtio standard.  FF-A is an
> Arm specification, but PCI is not, and virtio already references PCI.

Yes!

- Mani

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