Re: [PATCH v2 4/4] virtio-net: Add support for USO features

[Thomas Huth]

On 26/07/2024 08.08, Michael S. Tsirkin wrote:
> On Thu, Jul 25, 2024 at 06:18:20PM -0400, Peter Xu wrote:
> > On Tue, Aug 01, 2023 at 01:31:48AM +0300, Yuri Benditovich wrote:
> > > USO features of virtio-net device depend on kernel ability
> > > to support them, for backward compatibility by default the
> > > features are disabled on 8.0 and earlier.
> > >
> > > Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
> > > Signed-off-by: Andrew Melnychecnko <andrew@daynix.com>
> >
> > Looks like this patch broke migration when the VM starts on a host that has
> > USO supported, to another host that doesn't..
>
> This was always the case with all offloads. The answer at the moment is,
> don't do this.

May I ask for my understanding:
"don't do this" = don't automatically enable/disable virtio features in QEMU 
depending on host kernel features, or "don't do this" = don't try to migrate 
between machines that have different host kernel features?

> Long term, we need to start exposing management APIs
> to discover this, and management has to disable unsupported features.

Ack, this likely needs some treatments from the libvirt side, too.

 Thomas