PMU in KVM

PMU in KVM

[Arthur Chunqi Li]

Hi Gleb,

I noticed that arch/x86/kvm/pmu.c is on your management and I have
some questions about PMU in KVM. Thanks ahead if you can spare time
answering these questions.

1. How could PMU cooperate with Intel VT? For example, I only find
flags in IA32_PERFEVTSELx MSRs to count in OS and USER mode (Ring 0
and other rings). What is the consequence when I open VMXON with PMU
enabled? Can I distinguish the counts in root and non-root mode? I
cannot find the related descriptions in Intel manual.

2. What is the current status of vPMU in KVM? Is it auto-enabled? And
how can I use (or enable/disable) it?

Thanks,
Arthur

-- 
Arthur Chunqi Li
Department of Computer Science
School of EECS
Peking University
Beijing, China

Re: PMU in KVM

[Gleb Natapov]

On Tue, Nov 26, 2013 at 04:02:36PM +0800, Arthur Chunqi Li wrote:
> Hi Gleb,
> 
> I noticed that arch/x86/kvm/pmu.c is on your management and I have
> some questions about PMU in KVM. Thanks ahead if you can spare time
> answering these questions.
> 
> 1. How could PMU cooperate with Intel VT? For example, I only find
> flags in IA32_PERFEVTSELx MSRs to count in OS and USER mode (Ring 0
> and other rings). What is the consequence when I open VMXON with PMU
> enabled? Can I distinguish the counts in root and non-root mode? I
> cannot find the related descriptions in Intel manual.
> 
No you cannot. You can disable/enable PMU counters before/after
vmexit/vmentry and in this way know in what sate event was counted. That
what MPU emulation does.

> 2. What is the current status of vPMU in KVM? Is it auto-enabled? And
> how can I use (or enable/disable) it?
> 
If you run with -cpu host on Intel machine it will be enabled.

--
			Gleb.