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


  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Fri, 19 Mar 2021 12:59:38 +0000
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  • Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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On 16/03/2021 16:58, Jan Beulich wrote:
> On 16.03.2021 17:18, Andrew Cooper wrote:
>> In hindsight, this was a poor move.  Some of these MSRs require probing for,
>> causing unhelpful spew into xl dmesg, as well as spew from unit tests
>> explicitly checking behaviour.
> I can indeed see your point for MSRs that require probing. But what about
> the others (which, as it seems, is the majority)? And perhaps specifically
> what about the entire WRMSR side, which won't be related to probing? I'm
> not opposed to the change, but I'd like to understand the reasoning for
> every one of the MSRs, not just a subset.
>
> Of course such ever-growing lists of case labels aren't very nice - this
> going away was one of the things I particularly liked about the original
> change.

The logging in the default case is only useful when it is genuinely MSRs
we haven't considered.

It is very useful at pointing bugs in guests, or bugs in Xen, but only
when the logging is not drowned out by things we know about.

~Andrew




 


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