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

From: "Natarajan, Janakarajan" <Janakarajan.Natarajan@amd.com>
To: Borislav Petkov <bp@suse.de>, Paolo Bonzini <pbonzini@redhat.com>,
	Radim Krcmar <rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org, x86@kernel.org,
	linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
	Len Brown <len.brown@intel.com>, Kyle Huey <me@kylehuey.com>,
	Kan Liang <Kan.liang@intel.com>,
	Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Tony Luck <tony.luck@intel.com>
Subject: Re: [PATCH v2 3/4] Add support for AMD Core Perf Extension in guest
Date: Fri, 1 Dec 2017 13:30:15 -0600	[thread overview]
Message-ID: <8ff957e3-67b7-3986-05ef-3e42bd7143f6@amd.com> (raw)
In-Reply-To: <20171117114445.iv2s7sm2mjqusztx@pd.tnic>

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
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.

>