linux-kernel - Re: [tip:perf/core] perf/x86: Add an MSR PMU driver

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Message-ID: <20150806155943.GH25159@twins.programming.kicks-ass.net>
Date:	Thu, 6 Aug 2015 17:59:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"Liang, Kan" <kan.liang@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Lutomirski <luto@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:perf/core] perf/x86: Add an MSR PMU driver

On Thu, Aug 06, 2015 at 08:30:08AM -0700, Andy Lutomirski wrote:
> On Thu, Aug 6, 2015 at 8:21 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Tue, Aug 04, 2015 at 08:39:27PM +0000, Liang, Kan wrote:
> > -       default:
> > -               err = -ENOTSUPP;
> > +               if (!msr[i].test() || rdmsrl_safe(msr[i].msr, &val))
> > +                       msr[i].attr = NULL;
> 
> IIRC rdmsrl_safe literally never fails under QEMU TCG, and I'm not

*sigh* the borkage never stops does it :-(

> entirely sure what happens under KVM if emulation kicks in.  It might
> pay to keep the model check for the non-architectural stuff, or at
> least check for a nonzero return value.

Of course, 0 might be a valid value.. Esp. for the SMI counter.
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