Re: [PATCH] Documentation: KVM: Document guest-visible compatibility expectations

[Oliver Upton <oupton@kernel.org>]

On Wed, May 20, 2026 at 12:33:52AM +0100, David Woodhouse wrote:
> On Tue, 2026-05-19 at 15:57 -0700, Oliver Upton wrote:
> > What ifs and maybes do not meet the bar, in my opinion, for preserving
> > bug emulation in KVM. Of course there could be a little flexibility with
> > that but we need to have some way of discriminating between bug fixes
> > and genuine guest expectations around the behavior of virtual hardware.
> 
> I believe you have this completely backwards.

No, I really don't.

Leaving every bugfix that could _possibly_ have a guest-visible impact
subject to drive-by scrutiny many years after the dust has settled is
not an acceptable working dynamic. Especially since it would appear
that the rest of the ecosystem has long since moved on from this
particular issue.

If this matters to you so deeply then please, be part of the solution
instead. You may find that reviewing patches leads to better outcomes
than getting belligerent with the arm64 folks every time you guys
decide to rebase your kernel. Hell, hypotheticals actually have a lot
more weight in the context of a review. And if your testing is extensive
enough to catch these sort of subtleties, don't you think it's better
done against mainline?

Maybe it's just me but I am left feeling disappointed that we all
haven't found a productive way of working together. I've tried to bridge
the gap here; we obviously need to do something that at least fixes the
UAPI breakage. Although apparently we don't even care to meet that low
of bar.

> A stable and mature platform doesn't get to play in its ivory tower and
> randomly inflict breakage on guests because they "deserve it".

Really? Aren't you asking for us to emulate something completely broken
for you?

Thanks,
Oliver