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

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Date:   Fri, 5 Jul 2019 08:23:37 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>, kan.liang@...ux.intel.com
Cc:     mingo@...hat.com, jolsa@...nel.org, peterz@...radead.org,
        linux-kernel@...r.kernel.org, ak@...ux.intel.com
Subject: Re: [PATCH] perf/x86/intel: Fix spurious NMI on fixed counter



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()")
>> ---
>>   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@...nel.org>
> 
> thanks,
> jirka
> 

Hi,

Could this fix be accepted?

Thanks
Jin Yao

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