linux-kernel - Re: [PATCH] perf/x86/intel: Fix spurious NMI on fixed counter

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Date:   Fri, 5 Jul 2019 13:44:35 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Jin, Yao" <yao.jin@...ux.intel.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, kan.liang@...ux.intel.com,
        mingo@...hat.com, jolsa@...nel.org, linux-kernel@...r.kernel.org,
        ak@...ux.intel.com
Subject: Re: [PATCH] perf/x86/intel: Fix spurious NMI on fixed counter

On Fri, Jul 05, 2019 at 08:23:37AM +0800, Jin, Yao wrote:
> 
> 
> On 6/25/2019 10:58 PM, Jiri Olsa wrote:
> > On Tue, Jun 25, 2019 at 07:21:35AM -0700, kan.liang@...ux.intel.com wrote:
> > > From: Kan Liang <kan.liang@...ux.intel.com>
> > > 
> > > If a user first sample a PEBS event on a fixed counter, then sample a
> > > non-PEBS event on the same fixed counter on Icelake, it will trigger
> > > spurious NMI. For example,
> > > 
> > >    perf record -e 'cycles:p' -a
> > >    perf record -e 'cycles' -a
> > > 
> > > The error message for spurious NMI.
> > > 
> > >    [June 21 15:38] Uhhuh. NMI received for unknown reason 30 on CPU 2.
> > >    [  +0.000000] Do you have a strange power saving mode enabled?
> > >    [  +0.000000] Dazed and confused, but trying to continue
> > > 
> > > The issue was introduced by the following commit:
> > > 
> > >    commit 6f55967ad9d9 ("perf/x86/intel: Fix race in intel_pmu_disable_event()")
> > > 
> > > The commit moves the intel_pmu_pebs_disable() after
> > > intel_pmu_disable_fixed(), which returns immediately.
> > > The related bit of PEBS_ENABLE MSR will never be cleared for the fixed
> > > counter. Then a non-PEBS event runs on the fixed counter, but the bit
> > > on PEBS_ENABLE is still set, which trigger spurious NMI.
> > > 
> > > Check and disable PEBS for fixed counter after intel_pmu_disable_fixed().
> > > 
> > > Reported-by: Yi, Ammy <ammy.yi@...el.com>
> > > Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> > > Fixes: 6f55967ad9d9 ("perf/x86/intel: Fix race in intel_pmu_disable_event()")

> > oops, I overlooed this, looks good
> > 
> > Acked-by: Jiri Olsa <jolsa@...nel.org>

Have it now, thanks!