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

[Jiri Olsa <jolsa@redhat.com>]

On Tue, Jun 25, 2019 at 07:21:35AM -0700, kan.liang@linux.intel.com wrote:
> From: Kan Liang <kan.liang@linux.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@intel.com>
> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
> Fixes: 6f55967ad9d9 ("perf/x86/intel: Fix race in intel_pmu_disable_event()")
> ---
>  arch/x86/events/intel/core.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 4377bf6a6f82..464316218b77 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -2160,12 +2160,10 @@ static void intel_pmu_disable_event(struct perf_event *event)
>  	cpuc->intel_ctrl_host_mask &= ~(1ull << hwc->idx);
>  	cpuc->intel_cp_status &= ~(1ull << hwc->idx);
>  
> -	if (unlikely(hwc->config_base == MSR_ARCH_PERFMON_FIXED_CTR_CTRL)) {
> +	if (unlikely(hwc->config_base == MSR_ARCH_PERFMON_FIXED_CTR_CTRL))
>  		intel_pmu_disable_fixed(hwc);
> -		return;
> -	}
> -
> -	x86_pmu_disable_event(event);
> +	else
> +		x86_pmu_disable_event(event);
>  

oops, I overlooed this, looks good

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

>  	/*
>  	 * Needs to be called after x86_pmu_disable_event,
> -- 
> 2.14.5
>