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Re: [Xen-devel] [PATCH] Allow dom0 to write MSR IA32_ENERGY_PERF_BIAS

To: "Gang Wei" <gang.wei@xxxxxxxxx>,"Keir Fraser" <keir@xxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Allow dom0 to write MSR IA32_ENERGY_PERF_BIAS
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Wed, 05 Jan 2011 08:31:22 +0000
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>>> On 05.01.11 at 09:22, Keir Fraser <keir@xxxxxxx> wrote:
> On 05/01/2011 08:17, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>>>> On 05.01.11 at 09:13, Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:
>>> On 05/01/2011 07:59, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>>>>> Why would you allow this only if Dom0 has its vcpus pinned?
>>>>> It is meaningless if dom0 can't control all pcpus exactly. Only in case of
>>>>> dom0 vcpus pinned, it makes sense.
>>>> Disagree. The user mode tool could set its own affinity (virtual and
>>>> physical) and then issue the MSR write. Please don't enforce
>>>> restrictions where not really needed (I actually suppose that the
>>>> restriction should be removed for MSR_IA32_THERM_CONTROL too).
>>> If so, it deserves a separate patch to strip out *all* the is_pinned checks
>>> at the same time.
>> You certainly don't mean *all*, but yes, I'm intending to submit such
>> a patch.
> The ones in x86/traps.c (WRMSR emulation) and x86/domain.c
> (VCPUOP_get_physid) are both unnecessary, at least.

They aren't outright unnecessary I'd say, they just need some
relaxing (as the code makes sense also when the vCPU is
constrained to a single pCPU). That's the change I'm going to
send shortly.


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