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

Demi Marie Obenour
2026-02-25T12:53:43Z

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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?

> 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.
--
Sincerely,
Demi Marie Obenour (she/her/hers)

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