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

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Message-ID: <20171117114445.iv2s7sm2mjqusztx@pd.tnic>
Date:   Fri, 17 Nov 2017 12:44:45 +0100
From:   Borislav Petkov <bp@...e.de>
To:     "Natarajan, Janakarajan" <Janakarajan.Natarajan@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>
Cc:     kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, Len Brown <len.brown@...el.com>,
        Kyle Huey <me@...ehuey.com>, Kan Liang <Kan.liang@...el.com>,
        Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v2 3/4] Add support for AMD Core Perf Extension in guest

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...

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--