linux-kernel - Re: intel_pstate divide error with v3.13-rc4-256-gb7000ad

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Message-ID: <52CAE574.3010304@gmail.com>
Date:	Mon, 06 Jan 2014 09:18:44 -0800
From:	Dirk Brandewie <dirk.brandewie@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	Gleb Natapov <gleb@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Kashyap Chamarthy <kchamart@...hat.com>,
	Josh Boyer <jwboyer@...oraproject.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	"Richard W.M. Jones" <rjones@...hat.com>
Subject: Re: intel_pstate divide error with v3.13-rc4-256-gb7000ad

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

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