Re: [PATCH RFC for-4.15] x86/msr: introduce an option for legacy MSR behavior selection

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Jan Beulich writes ("Re: [PATCH RFC for-4.15] x86/msr: introduce an option for 
legacy MSR behavior selection"):
> On 04.03.2021 11:05, Roger Pau Monné wrote:
...
> > This one seems like a fine candidate to implement in
> > svm_msr_read_intercept, because Xen needs to return a specific value
> > for this MSR.
> > 
> > Regarding the global approach to fixing the fallout from the MSR
> > policy change, I don't see why we couldn't do a mix between pro-active
> > and reactive.
> > 
> > I think we must have an option to fallback to something similar to the
> > old policy for HVM guests so that users have a way to get their guests
> > running after an update without requiring a code change.
> > 
> > That doesn't mean we can't reactively add the missing MSRs as we go
> > discovering them. I would even print a warning when using such
> > fallback legacy MSR handling option that you need to report the issue
> > to xen-devel because the option might be removed in future releases.
> > 
> > Does the above seem like a sensible plan?
> 
> I think so, yes. I wonder what Andrew thinks, though.

FTR I am on board with this plan.  I would like to see quick progress
on this issue as it seems like one of the major risks in the release.

Thanks,
Ian.