linux-kernel - Re: [PATCH 2/6] KVM: x86: selftests: Define AMD PMU CPUID leaves

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Message-ID: <ZtDZMZgYp7F6e_Qd@google.com>
Date: Thu, 29 Aug 2024 13:25:21 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Colton Lewis <coltonlewis@...gle.com>
Cc: Mingwei Zhang <mizhang@...gle.com>, kvm@...r.kernel.org, ljr.kernel@...il.com, 
	jmattson@...gle.com, aaronlewis@...gle.com, pbonzini@...hat.com, 
	shuah@...nel.org, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] KVM: x86: selftests: Define AMD PMU CPUID leaves

On Wed, Aug 28, 2024, Colton Lewis wrote:
> Hi Mingwei, thanks for reviewing!
> 
> Mingwei Zhang <mizhang@...gle.com> writes:
> 
> > On Tue, Aug 13, 2024, Colton Lewis wrote:
> > > This defined the CPUID calls to determine what extensions and
> > > properties are available. AMD reference manual names listed below.
> 
> > > * PerfCtrExtCore (six core counters instead of four)
> > > * PerfCtrExtNB (four counters for northbridge events)
> > > * PerfCtrExtL2I (four counters for L2 cache events)
> > > * PerfMonV2 (support for registers to control multiple
> > >    counters with a single register write)
> > > * LbrAndPmcFreeze (support for freezing last branch recorded stack on
> > >    performance counter overflow)
> > > * NumPerfCtrCore (number of core counters)
> > > * NumPerfCtrNB (number of northbridge counters)
> 
> > > Signed-off-by: Colton Lewis <coltonlewis@...gle.com>
> > > ---
> > >   tools/testing/selftests/kvm/include/x86_64/processor.h | 7 +++++++
> > >   1 file changed, 7 insertions(+)
> 
> > > diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h
> > > b/tools/testing/selftests/kvm/include/x86_64/processor.h
> > > index a0c1440017bb..9d87b5f8974f 100644
> > > --- a/tools/testing/selftests/kvm/include/x86_64/processor.h
> > > +++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
> > > @@ -183,6 +183,9 @@ struct kvm_x86_cpu_feature {
> > >   #define	X86_FEATURE_GBPAGES		KVM_X86_CPU_FEATURE(0x80000001, 0, EDX, 26)
> > >   #define	X86_FEATURE_RDTSCP		KVM_X86_CPU_FEATURE(0x80000001, 0, EDX, 27)
> > >   #define	X86_FEATURE_LM			KVM_X86_CPU_FEATURE(0x80000001, 0, EDX, 29)
> > > +#define	X86_FEATURE_PERF_CTR_EXT_CORE	KVM_X86_CPU_FEATURE(0x80000001,
> > > 0, ECX, 23)
> > > +#define	X86_FEATURE_PERF_CTR_EXT_NB	KVM_X86_CPU_FEATURE(0x80000001,
> > > 0, ECX, 24)
> > > +#define	X86_FEATURE_PERF_CTR_EXT_L2I	KVM_X86_CPU_FEATURE(0x80000001,
> > > 0, ECX, 28)
> 
> > You won't be testing Northbridge counters and L2I counters, so these two
> > could be optional to the patch.
> 
> That's correct. Since it was a small thing to include I thought it best
> to include and save someone in the future from digging through the
> reference manual again.

+1.  They're defines, i.e. have no meaningful cost.  And anything that *might*
save me from having to find CPUID entries in the SDM/APM is worth adding.