Date: Thu, 6 Aug 2015 17:59:43 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "Liang, Kan" <kan.liang@intel.com>, Thomas Gleixner <tglx@linutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Andrew Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        "linux-tip-commits@vger.kernel.org" 
	<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:perf/core] perf/x86: Add an MSR PMU driver
Message-ID: <20150806155943.GH25159@twins.programming.kicks-ass.net>
References: <1437407346-31186-1-git-send-email-kan.liang@intel.com>
 <tip-b7b7c7821d932ba18ef6c8eafc8536066b4c2ef4@git.kernel.org>
 <CALCETrXffVT=KQpURGLEAXH5x6KxXhYuicGgk3hmF8-QGT81jw@mail.gmail.com>
 <37D7C6CF3E00A74B8858931C1DB2F077018D16F1@SHSMSX103.ccr.corp.intel.com>
 <CALCETrXUdBs==s-dBfugshyFdG_nBn=qd2MKYLwmXYx_r43Vvg@mail.gmail.com>
 <37D7C6CF3E00A74B8858931C1DB2F077018D206A@SHSMSX103.ccr.corp.intel.com>
 <CALCETrXP0-jRiq_qz=hwPxjMxGrbke9rtembh4_XBq-vq+cPNg@mail.gmail.com>
 <37D7C6CF3E00A74B8858931C1DB2F077018D2103@SHSMSX103.ccr.corp.intel.com>
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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@infradead.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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