Re: [Xen-devel] [PATCH 06/10] x86/cpuid: Handle leaf 0x6 in guest_cpuid()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.02.17 at 10:12, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 22/02/17 08:23, Andrew Cooper wrote:
>> On 22/02/17 07:31, Jan Beulich wrote:
>>>>>> On 21.02.17 at 18:40, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> On 21/02/17 17:25, Jan Beulich wrote:
>>>>>>>> On 20.02.17 at 12:00, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>>>> The PV MSR handling logic as minimal support for some thermal/perf 
>>>>>> operations
>>>>>> from the hardware domain, so leak through the implemented subset of 
>>>>>> features.
>>>>> Does it make sense to continue to special case PV hwdom here?
>>>> Being able to play with these MSRs will be actively wrong for HVM
>>>> context.  It is already fairly wrong for PV context, as nothing prevents
>>>> you being rescheduled across pcpus while in the middle of a read/write
>>>> cycle on the MSRs.
>>> So the MSRs in question are, afaics
>>> - MSR_IA32_MPERF, MSR_IA32_APERF, MSR_IA32_PERF_CTL (all
>>>   of which are is_cpufreq_controller() dependent)
>>> - MSR_IA32_THERM_CONTROL, MSR_IA32_ENERGY_PERF_BIAS
>>>   (both of which are is_pinned_vcpu() dependent)
>>> For the latter your argument doesn't apply. For the former, I've
>>> been wondering for a while whether we shouldn't do away with
>>> "cpufreq=dom0-kernel".
>> Hmm.  All good points.  If I can get away without leaking any of this,
>> that would be ideal.  (Lets see what Linux thinks of such a setup.)
> 
> Linux seems fine without any of this leakage.

But is that for a broad range of versions, or just the one you had
to hand?

Jan


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