Re: [PATCH 1/3] Revert "x86/msr: drop compatibility #GP handling in guest_{rd,wr}msr()"

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Andrew Cooper writes ("Re: [PATCH 1/3] Revert "x86/msr: drop compatibility #GP 
handling in guest_{rd,wr}msr()""):
> On 17/03/2021 13:37, Ian Jackson wrote:
> > AFAICT there is no explanation for why patches 1/ and 2/ deserve to go
> > into 4.15.

I see now, rereading the thread, that there was a sentence about this
in each patch betwen the commit message and the diff.  Sorry for
missing that.  (Although TBH at least one of those messages could
usefully have gone into the commit message, as useful motivational
background.)

> >   We are late in the freeze now, so I would ideally be
> > looking for a clear and compelling argument.  I'd also like to
> > understand what the risks are of taking these.  Can someone please
> > enlighten me ?
> 
> To make the code in 4.15 match 4.14, so patch 3 can be written in the
> first place.
> 
> Also, as a side benefit, patches 1 and 2 reduce the quantity of logspew
> from the impacted MSRs.
> 
> We cannot simply take patch 3 as-is, and say "4.14 and earlier" for
> backport, because that still forces end users to specify msr_relaxed to
> unbreak their Solaris guests, which is usability regression vs 4.14

This is plausible and going in the right direction but I still feel
uncertain.

Jan, what is your summary opinion about patch 3 ?

Roger, can I get your opinion about the possible downside risks of
this patch ?

Thanks,
Ian.