Re: [PATCH v2 3/4] Add support for AMD Core Perf Extension in guest

[Natarajan, Janakarajan]

On 12/5/2017 11:56 AM, Radim Krcmar wrote:
> 2017-12-01 13:30-0600, Natarajan, Janakarajan:
> > On 11/17/2017 5:44 AM, Borislav Petkov wrote:
> > > On Thu, Nov 16, 2017 at 12:00:11PM -0600, Natarajan, Janakarajan wrote:
> > > > Ah my apologies. So when the pmu is initialized the cpuid entries
> > > > aren't available then.
> > > So let's see:
> > >
> > > ... kvm_arch_vcpu_create() ->
> > > svm_create_vcpu() ->
> > > kvm_vcpu_init() ->
> > > kvm_arch_vcpu_init() ->
> > >
> > > <--- HERE
> > >
> > > kvm_pmu_init()
> > >
> > > But at HERE in kvm_arch_vcpu_init() right before kvm_pmu_init() we do already query
> > > cpuid:
> > >
> > > 	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
> > >
> > > so it's not like we don't know about cpuid leafs at that point. Which
> > > would mean that the code can be made to set the CPU family earlier,
> > > before kvm_pmu_init() runs so that you have the proper CPU family and
> > > thus have this thing properly designed.
> > >
> > > Maybe Paolo and Radim have a better suggestion here...
> > Paolo, Radim any suggestions about this. I feel that the number of counters
> > initialized can be 6
> This is the best solution with the current framework.

Okay.

> > and the subsequent code (kvm_pmu_refresh()) takes care of the number of
> > counters to be used (4 or 6)
> > based on the vcpu family.
> Can't we look only at X86_FEATURE_PERFCTR_CORE and completely ignore the
> AMD family?
> Using the family would bring problems with compatiblity.

Yeah. We can just use the X86_FEATURE_PERFCTR_CORE flag as a check. I'll 
send a v3
with the changes.

Thanks.

> Thanks.