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

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 17/03/2021 13:37, Ian Jackson wrote:
> I have read this thread and with my release manager hat on I feel
> confused and/or ignorant.
>
> Patch 3/ has a good explanation of what the problem is it is
> addressing and why this is important for 4.15.  But then there is
> Jan's most recent reply starting "I find all of this confusing".  Jan,
> can you please tell me in words of one syllable what the implication
> of that message is ?  In particular is any of what you say a reason
> for me to withhold my release-ack ?
>
> AFAICT there is no explanation for why patches 1/ and 2/ deserve to go
> into 4.15.  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

~Andrew