linux-kernel - Re: Drop WARN on AMD lack of perfctrs

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Date:	Fri, 17 May 2013 11:27:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Robert Richter <rric@...nel.org>, Josh Boyer <jwboyer@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	x86@...nel.org, linux-kernel@...r.kernel.org, gleb@...hat.com
Subject: Re: Drop WARN on AMD lack of perfctrs

On Fri, May 17, 2013 at 11:16:51AM +0200, Borislav Petkov wrote:
> On Fri, May 17, 2013 at 11:04:51AM +0200, Peter Zijlstra wrote:
> > Mostly so that check_hw_exists() doesn't need to know about the vendor
> > specifics like where the MSRs live, how many there are etc..
> 
> Yep, but there will still be issues with perf when booted on a guest and
> kvm not supporting it. And AFAIU, they're signalling this by turning off
> CPUID bits so that initializing perf doesn't happen.
> 
> So, I think init_hw_perf_events should as a first step look at CPUID
> bits and then do anything else. And this is done on Intel with
> X86_FEATURE_ARCH_PERFMON. But Robert is fixing this on AMD too so...

But not all x86 hardware even has the stuff enumerated in CPUID, and afaict
Intel and AMD use a different CPUID bit as well, so what's
init_hw_perf_events() to do?
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