Re: [Xen-devel] [PATCH] x86: log XPTI enabled status

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.02.18 at 13:29, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 01/02/18 08:52, Jan Beulich wrote:
>> At the same time also report the state of the two defined
>> ARCH_CAPABILITIES MSR bits (but don't expose the MSR to guests yet).
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> Should we disable XPTI right here when we find RDCL_NO?
> 
> I was planning to wait for a working piece of hardware before trying to
> implement ARCH_CAPS, given how often the spec changed.  Then again, at
> the point Linux is doing this, we might as well consider it safe.

I have no idea how far Linux has progressed in that direction, so I
can't decide whether this is a "yes" or a "let's better wait".

>> --- a/xen/include/public/arch-x86/cpufeatureset.h
>> +++ b/xen/include/public/arch-x86/cpufeatureset.h
>> @@ -244,6 +244,7 @@ XEN_CPUFEATURE(AVX512_4VNNIW, 9*32+ 2) /
>>  XEN_CPUFEATURE(AVX512_4FMAPS, 9*32+ 3) /*A  AVX512 Multiply Accumulation 
>> Single Precision */
>>  XEN_CPUFEATURE(IBRSB,         9*32+26) /*A  IBRS and IBPB support (used by 
>> Intel) */
>>  XEN_CPUFEATURE(STIBP,         9*32+27) /*A! STIBP */
>> +XEN_CPUFEATURE(ARCH_CAPS,     9*32+29) /*   IA32_ARCH_CAPABILITIES MSR */
> 
> This doesn't appear to be used?

See the conditional around rdmsrl(MSR_ARCH_CAPABILITIES, caps).

Jan


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