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Date:   Mon, 27 Nov 2017 12:21:37 -0600
From:   "Natarajan, Janakarajan" <>
To:     Borislav Petkov <>, Paolo Bonzini <>,
        Radim Krcmar <>
        Thomas Gleixner <>,
        Ingo Molnar <>,
        "H . Peter Anvin" <>, Len Brown <>,
        Kyle Huey <>, Kan Liang <>,
        Grzegorz Andrejczuk <>,
        Tom Lendacky <>,
        Tony Luck <>
Subject: Re: [PATCH v2 3/4] Add support for AMD Core Perf Extension in guest

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);

cpuid_query_maxphyaddr first checks for for the 0x80000008 cpuid entry, 
and if it can't find it
returns a default value of 36.

When invoked in the kvm_arch_vcpu_init(), the default is being returned. 
The vcpu->arch.maxphyaddr
is later updated in the kvm_update_cpuid(), which in my case was setting 
the maxphyaddr to 40.
I believe the cpuid entry is not available when invoked in the init call 
and a default value is
being used as a placeholder until the entries are updated by qemu.

> 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...

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