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 16:57:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
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 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.