Re: Ping²: [PATCH] x86/PV: conditionally avoid raising #GP for early guest MSR accesses

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.02.2021 11:56, Jürgen Groß wrote:
> As we need to consider backports of processor bug mitigations
> in old guests, too, I think we need to have a "catch-all"
> fallback.
> 
> Not being able to run an old updated guest until we add handling
> for a new MSR isn't a viable option IMO.

I'm not sure I follow you here: Such backports should still make
use of the respective CPUID bits, and hence shouldn't contain
"blind" MSR accesses. And if there's really something needing to
probe an MSR, then I'd expect such a backport to make sure the
probing actually works in a prereq (presumably) backport.

Jan