linux-kernel - Re: [PATCH] perf/x86/intel: Use rdmsrl

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Message-ID: <20140314161745.GH3793@tassilo.jf.intel.com>
Date:	Fri, 14 Mar 2014 09:17:45 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Venkatesh Srinivas <venkateshs@...gle.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Stephane Eranian <eranian@...gle.com>, mingo@...e.hu,
	zheng.z.yan@...el.com
Subject: Re: [PATCH] perf/x86/intel: Use rdmsrl_safe when initializing RAPL
 PMU.

> The Intel ISR section for RDMSR seems to say: "Specifying a reserved
> or unimplemented
> MSR address in ECX will also cause a general protection exception".
> 
> From a guest's perspective, MSR_RAPL_POWER_UNIT is unimplemented; kvm matches
> this behavior.

MSRs are model specific and defined per model number. If you report a model
number you're expected to implement the MSRs defined for that model number.

AFAIK Xen just reports 0 for unknown MSRs (and I'm surprised KVM doesn't too)

I would suggest to fix KVM.

-Andi 
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