Re: [PATCH v2 0/2] kvm: x86: Emulate MSR_PLATFORM_INFO

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On Tue, Jun 18, 2013 at 8:16 AM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
> On Tue, Jun 18, 2013 at 04:05:08PM +0200, Paolo Bonzini wrote:
>> Il 05/06/2013 10:42, Gleb Natapov ha scritto:
>> >> > These patches add an emulated MSR_PLATFORM_INFO that kvm guests
>> >> > can read as described in section 14.3.2.4 of the Intel SDM.
>> >> > The relevant changes and details are in [2/2]; [1/2] makes vendor_intel
>> >> > generic. There are atleat two known applications that fail to run because
>> >> > of this MSR missing - Sandra and vTune.
>> > So I really want Intel opinion on this. Right now it is impossible to
>> > implement the MSR correctly in the face of migration (may be with tsc
>> > scaling it will be possible) and while it is unimplemented if application
>> > tries to use it it fails, but if we will implement it application will
>> > just produce incorrect result without any means for user to detect it.
>>
>> Jun, ping?  (Perhaps Gleb you want to ask a more specific question though).
>>
>> I don't think this is much different from any other RDTSC usage in
>> applications (they will typically do their calibration manually, and do
>> it just once).  I'm applying it to queue.
>>
> And we do not support application that uses RDTSC directly! If we could
> catch those it would be good from support point of view, so the way
> MSR_PLATFORM_INFO behaves now it better then proposed alternative.

Is it reasonable or possible to expose MSR_PLATFORM_INFO more and then
disable migration? Some use cases (like VTune) don't need live
migration.


--
Jun
Intel Open Source Technology Center
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