Re: Virtio in Xen on Arm (based on IOREQ concept)

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 17 Jul 2020, Oleksandr wrote:
> > > *A few word about solution:*
> > > As it was mentioned at [1], in order to implement virtio-mmio Xen on Arm
> > Any plans for virtio-pci? Arm seems to be moving to the PCI bus, and
> > it would be very interesting from a x86 PoV, as I don't think
> > virtio-mmio is something that you can easily use on x86 (or even use
> > at all).
> 
> Being honest I didn't consider virtio-pci so far. Julien's PoC (we are based
> on) provides support for the virtio-mmio transport
> 
> which is enough to start working around VirtIO and is not as complex as
> virtio-pci. But it doesn't mean there is no way for virtio-pci in Xen.
> 
> I think, this could be added in next steps. But the nearest target is
> virtio-mmio approach (of course if the community agrees on that).

Hi Julien, Oleksandr,

Aside from complexity and easy-of-development, are there any other
architectural reasons for using virtio-mmio?

I am not asking because I intend to suggest to do something different
(virtio-mmio is fine as far as I can tell.) I am asking because recently
there was a virtio-pci/virtio-mmio discussion recently in Linaro and I
would like to understand if there are any implications from a Xen point
of view that I don't yet know.

For instance, what's your take on notifications with virtio-mmio? How
are they modelled today? Are they good enough or do we need MSIs?