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Date: Mon, 06 Jan 2014 09:18:44 -0800
From: Dirk Brandewie <dirk.brandewie@gmail.com>
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To: Paolo Bonzini <pbonzini@redhat.com>
CC: Gleb Natapov <gleb@kernel.org>, "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Kashyap Chamarthy <kchamart@redhat.com>,
        Josh Boyer <jwboyer@fedoraproject.org>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        "cpufreq@vger.kernel.org" <cpufreq@vger.kernel.org>,
        Linux PM list <linux-pm@vger.kernel.org>,
        "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
        "Richard W.M. Jones" <rjones@redhat.com>
Subject: Re: intel_pstate divide error with v3.13-rc4-256-gb7000ad
References: <CA+5PVA6YpKc6kYK5UiTnGLZpB8uts=-QPtyhotAyZ2kuoG8PPQ@mail.gmail.com> <4794554.Hmd2RUNYDT@vostro.rjw.lan> <52C18A23.10703@redhat.com> <3710588.K8glfx1cYs@vostro.rjw.lan> <52C6F3B4.3050904@gmail.com> <20140103180435.GK10961@minantech.com> <52C716C1.6070704@gmail.com> <52C7345D.30603@redhat.com>
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On 01/03/2014 02:06 PM, Paolo Bonzini wrote:
> Il 03/01/2014 21:00, Dirk Brandewie ha scritto:
>> +    case MSR_IA32_MPERF:
>> +    case MSR_IA32_APERF:
>
OK I will spin the patch to only add MSR_PLATFORM_INFO.

> These should never be accessed.  A KVM VM will always have
> CPUID[06H].ECX = 0, and the Intel manual says that the MSRs are only
> present if CPUID returns that value with bit 0 set.
>
> I think the actual bug is that intel_pstate_init does not check the
> feature bits in CPUID (either manually or via x86_match_cpu).

I will add the feature check.

What are the differences between the first and the nested KVM's?
At load time intel_pstate checks that APERF and MPERF are incrementing
and that PLATFORM_INFO has some value.  Somehow these checks pass
in the nested environment and we fall over when the CPU is being added
by cpufreq.

--Dirk