linux-kernel - Re: [PATCH] perf/x86/intel: Don't enable freeze-on-smi for PerfMon V1

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Date:   Wed, 25 Apr 2018 11:11:19 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, mingo@...hat.com, linux-kernel@...r.kernel.org,
        acme@...hat.com, eranian@...gle.com, ak@...ux.intel.com
Subject: Re: [PATCH] perf/x86/intel: Don't enable freeze-on-smi for PerfMon V1



On 4/25/2018 10:57 AM, Peter Zijlstra wrote:
> On Tue, Apr 24, 2018 at 03:56:23PM -0400, kan.liang@...ux.intel.com wrote:
>> From: Kan Liang <kan.liang@...ux.intel.com>
>>
>> The SMM freeze feature was introduced since PerfMon V2. But the current
>> code unconditionally enables the feature for all platforms. It can
>> generate #GP exception, if the related FREEZE_WHILE_SMM bit is set for
>> the machine with PerfMon V1.
>>
>> Checking the PerfMon version. Only enable the feature for PerfMon V2 and
>> later.
> 
> That's fine..
> 
>>
>> Fixes: 6089327f5424 ("perf/x86: Add sysfs entry to freeze counters on SMI")
>> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
>> ---
>>   arch/x86/events/intel/core.c | 9 ++++++---
>>   1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
>> index 4f2a5c7..08be8ed 100644
>> --- a/arch/x86/events/intel/core.c
>> +++ b/arch/x86/events/intel/core.c
>> @@ -3346,7 +3346,8 @@ static void intel_pmu_cpu_starting(int cpu)
>>   
>>   	cpuc->lbr_sel = NULL;
>>   
>> -	flip_smm_bit(&x86_pmu.attr_freeze_on_smi);
>> +	if (x86_pmu.version > 1)
>> +		flip_smm_bit(&x86_pmu.attr_freeze_on_smi);
>>   
>>   	if (!cpuc->shared_regs)
>>   		return;
> 
> And the above chunk does as advertised.
> 
>> @@ -3509,6 +3510,8 @@ static __initconst const struct x86_pmu core_pmu = {
>>   	.cpu_dying		= intel_pmu_cpu_dying,
>>   };
>>   
>> +static struct attribute *intel_pmu_attrs[];
>> +
>>   static __initconst const struct x86_pmu intel_pmu = {
>>   	.name			= "Intel",
>>   	.handle_irq		= intel_pmu_handle_irq,
>> @@ -3540,6 +3543,8 @@ static __initconst const struct x86_pmu intel_pmu = {
>>   	.format_attrs		= intel_arch3_formats_attr,
>>   	.events_sysfs_show	= intel_event_sysfs_show,
>>   
>> +	.attrs			= intel_pmu_attrs,
>> +
>>   	.cpu_prepare		= intel_pmu_cpu_prepare,
>>   	.cpu_starting		= intel_pmu_cpu_starting,
>>   	.cpu_dying		= intel_pmu_cpu_dying,
>> @@ -3918,8 +3923,6 @@ __init int intel_pmu_init(void)
>>   
>>   	x86_pmu.max_pebs_events		= min_t(unsigned, MAX_PEBS_EVENTS, x86_pmu.num_counters);
>>   
>> -
>> -	x86_pmu.attrs			= intel_pmu_attrs;
>>   	/*
>>   	 * Quirk: v2 perfmon does not report fixed-purpose events, so
>>   	 * assume at least 3 events, when not running in a hypervisor:
> 
> But what is all this about? The Changelog doesn't mention anything about
> this. Looks like an unrelated cleanup that really should've been a
> separate patch or something.

Only if the PerfMon version >= V2, the intel_pmu can be applied.
Moving intel_pmu_attrs to intel_pmu, which guarantees the feature can 
only be enabled for V2 and later.

I will modify the change log to explicitly mention it.

Thanks,
Kan