Re: [Xen-devel] [PATCH for-4.11] x86/msr: Correct the emulation behaviour of MSR_PRED_CMD

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.04.18 at 13:19, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 16/04/18 12:12, Jan Beulich wrote:
>>>>> On 16.04.18 at 12:56, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> The behaviour of reserved bits in MSR_PRED_CMD changed between beta and
>>> production microcode, and now raises a #GP fault for set reserved bits.
>> Interesting - quite unfortunate a change. Plus - I can't find where this is 
>> being
>> said.
> 
> Its not, but the new behaviour can be demonstrated easily.  Those with
> the beta microcode can confirm that the old behaviour was to ignore.
> 
> FWIW, ignoring reserved bits was always dubious, and I only implemented
> it like that to match how hardware behaved.  This new behaviour is far
> more sane.

Fully agree - should have been that way from the beginning.

Jan



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