Re: virtio-vsock requires 'disable-legacy=on' in QEMU 5.1

[Stefano Garzarella]

On Tue, Aug 18, 2020 at 04:31:01PM +0200, Cornelia Huck wrote:
> On Tue, 18 Aug 2020 16:01:20 +0200
> Stefano Garzarella <sgarzare@redhat.com> wrote:
> 
> > On Tue, Aug 18, 2020 at 02:44:50PM +0200, Cornelia Huck wrote:
> 
> > > It seems to me that the status before this was "works by accident, but
> > > only if we're not negotiating to legacy, or the guest/host are both
> > > little endian". IOW, no visible breakage for most people (or we'd
> > > probably have heard of it already). Now we have a setup that's correct,
> > > but forces users to adapt their QEMU command lines. Option 1 would
> > > eliminate the need to do that, but would cause possibly
> > > not-really-fixable migration issues (you can probably deal with that
> > > manually, detaching and re-attaching the device as a last resort.)
> > > 
> > > So, force modern, probably also remove the -transitional device type,
> > > and put a prominent explanation into the change log?
> > >   
> > 
> > I completely agree with your analysis and solution.
> > 
> > So, for now we need to patch vhost-vsock-pci and vhost-user-vsock-pci,
> > and queue the patches in stable.
> 
> I think we should also change -ccw; even though users won't get an
> error when starting QEMU, they might still run into the legacy problems
> in theory.

Okay.

> 
> Not sure how fast we'll have a stable release, though.
> 
> > 
> > Do you prefer to send them? Otherwise I can do that.
> 
> If you already have something on your disk, please go ahead :)

Yes, I have something for pci, and I'll follow your suggestion for ccw!

If you have time, can you share with me some tips on how to install
s390x guest on my laptop?

> 
> > 
> > Thanks again for the help and the test with s390x guest!
> 
> np; especially as it was my patch which started this in the first place
> :/
> 

I'm not sure that was a bad thing, since we found out that virtio-vsock is
modern only :-)

Thanks,
Stefano