Re: [VirtIO] Support for various devices in Xen

[Vikram Garhwal <vikram.garhwal@amd.com>]

Hi Andrei & Stefano,
On Thu, Jan 11, 2024 at 04:35:22PM -0800, Stefano Stabellini wrote:
> Hi Andrei,
> 
> Great that you are working with Xen and virtio. We at AMD are very
> interested in it as well.
> 
> I'll let Artem (CCed) and his team comment about the xen-troops
> repository.
> 
> I can share that from our side we are working toward adding complete
> support for using QEMU as virtio-backends provider. Vikram (CCed)
> managed to get virtio-net to work with the backend in QEMU. He should be
> able to provide instructions. We want to get those patches upstream in
> Xen and QEMU as soon as possible.
Actually, QEMU patches are already upstreamed for virtio-blk and virtio-net
devices available in v8.2.0.
For virtio with grants, the patches are WiP.

On Xen side, we are yet to upstream xen-tools patches which basically generate
the right arguments when invoking QEMU.
Here are down stream patches if you want:
1. https://github.com/Xilinx/xen/commit/be35b46e907c7c78fd23888d837475eb28334638
2. For Virtio disk backend:
    https://github.com/Xilinx/xen/commit/947280803294bbb963f428423f679d074c60d632
3. For Virtio-net:
    https://github.com/Xilinx/xen/commit/32fcc702718591270e5c8928b7687d853249c882
4. For changing the machine name to Xenpvh(to align with QEMU changes):
    https://github.com/Xilinx/xen/commit/5f669949c9ffdb1947cb47038956b5fb8eeb072a
> 
> The libxl changes are lagging behind a bit and you might have to use
> device_model_args to enable virtio backends in QEMU.
But QEMU 8.2.0 can still be used for virtio-net on ARM.

@Andrei here is an example on how to use virtio-net with QEMU:
    -device virtio-net-device,id=nic0,netdev=net0,mac=00:16:3e:4f:43:05 \
    -netdev type=tap,id=net0,ifname=vif1.0-emu,br=xenbr0,script=no,downscript=no\
    -machine xenpvh

Please make sure to use xenpvh as QEMU machine.

Regards,
Vikram
> 
> For SCMI, I'll let Bertrand (CCed) comment.
> 
> Cheers,
> 
> Stefano
> 
> 
> On Thu, 11 Jan 2024, Andrei Cherechesu (OSS) wrote:
> > Hello,
> > 
> > As I've mentioned in previous discussion threads in the xen-devel
> > community, we are running Xen 4.17 (uprev to 4.18 in progress) on NXP
> > S32G automotive processors (Cortex-A53 cores) and we wanted to know more
> > about the support for various VirtIO device types in Xen.
> > 
> > In the Xen 4.17 release notes, the VirtIO standalone backends mentioned
> > as supported and tested are: virtio-disk, virtio-net, virtio-i2c and
> > virtio-gpio.
> > 
> > However, we've only managed to successfully set up and try some
> > use-cases with the virtio-disk standalone backend [0] (which Olexandr
> > provided) based on the virtio-mmio transport.
> > 
> > As such, we have a few questions, which we haven't been able to figure
> > out from the mailing list discussions and/or code:
> >     1. Are there any plans for the virtio-disk repo to have a stable
> >     version? Is it going to be long-term hosted and maintained in the
> >     xen-troops github repo? Or was it just an one-time PoC implementation
> > 
> >     and the strategy for future VirtIO devices will be based on a more generic
> > 
> >     approach (i.e., without need for a specific standalone app)?
> > 
> > 
> >     2. With regards to the other backends, we want to try out and provide PV
> > 
> >     networking to a DomU based on virtio-net, but we haven't found any available
> > 
> >     resources for it (e.g., the standalone backend implementation if needed for
> > 
> >     control plane, configuration examples, presentations, demos, docs). Does it
> > 
> >     rely on the QEMU virtio-net or vhost implementation? Are there any examples
> > 
> >     on how to set it up? Any required Xen/Linux Kernel/QEMU versions?
> > 
> > 
> >     3. What other VirtIO device types are there planned to be supported in Xen?
> > 
> >     I'm supposing libxl will also need changes to accomodate new configuration
> > 
> >     parameters for each of them. Or is there something I'm missing?
> > 
> > 
> >     4. Also, while we're at it, are there any plans regarding SCMI
> >     awareness for Xen (e.g., SCMI Mediator - where the RFC thread from 2022
> > 
> >     seems discontinued)? Or is the preferred approach for sharing SCMI access
> > 
> >     to guests through virtio-scmi?
> > 
> > Thank you very much for the support, once again, and we're also looking
> > forward to the progress on the rust-vmm initiative.
> > 
> > Regards,
> > Andrei Cherechesu,
> > NXP Semiconductors
> > 
> > [0] https://github.com/xen-troops/virtio-disk
> > 
> > 
> >