RE: [PATCH V5] perf/x86: add sysfs entry to freeze counter on SMI

["Liang, Kan" <kan.liang@intel.com>]

Ping.
Any comments for the patch?

Thanks,
Kan

> Subject: [PATCH V5] perf/x86: add sysfs entry to freeze counter on SMI
> 
> From: Kan Liang <Kan.liang@intel.com>
> 
> Currently, the SMIs are visible to all performance counters. Because many
> users want to measure everything including SMIs. But in some cases, the SMI
> cycles should not be count. For example, to calculate the cost of SMI itself. So
> a knob is needed.
> 
> When setting FREEZE_WHILE_SMM bit in IA32_DEBUGCTL, all performance
> counters will be effected. There is no way to do per-counter freeze on SMI.
> So it should not use the per-event interface (e.g. ioctl or event attribute) to
> set FREEZE_WHILE_SMM bit.
> 
> Adds sysfs entry /sys/device/cpu/freeze_on_smi to set FREEZE_WHILE_SMM
> bit in IA32_DEBUGCTL. When set, freezes perfmon and trace messages while
> in SMM.
> Value has to be 0 or 1. It will be applied to all processors.
> Also serialize the entire setting so we don't get multiple concurrent threads
> trying to update to different values.
> 
> Signed-off-by: Kan Liang <Kan.liang@intel.com>
> ---
> 
> Changes since V4:
>  - drop msr_flip_bit function
>  - Use on_each_cpu() which already include all the needed protection
>  - Some small changes according to the comments
> 
>  arch/x86/events/core.c           | 10 +++++++
>  arch/x86/events/intel/core.c     | 63
> ++++++++++++++++++++++++++++++++++++++++
>  arch/x86/events/perf_event.h     |  3 ++
>  arch/x86/include/asm/msr-index.h |  2 ++
>  4 files changed, 78 insertions(+)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index
> 349d4d1..c16fb50 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -1750,6 +1750,8 @@ ssize_t x86_event_sysfs_show(char *page, u64
> config, u64 event)
>  	return ret;
>  }
> 
> +static struct attribute_group x86_pmu_attr_group;
> +
>  static int __init init_hw_perf_events(void)  {
>  	struct x86_pmu_quirk *quirk;
> @@ -1813,6 +1815,14 @@ static int __init init_hw_perf_events(void)
>  			x86_pmu_events_group.attrs = tmp;
>  	}
> 
> +	if (x86_pmu.attrs) {
> +		struct attribute **tmp;
> +
> +		tmp = merge_attr(x86_pmu_attr_group.attrs, x86_pmu.attrs);
> +		if (!WARN_ON(!tmp))
> +			x86_pmu_attr_group.attrs = tmp;
> +	}
> +
>  	pr_info("... version:                %d\n",     x86_pmu.version);
>  	pr_info("... bit width:              %d\n",     x86_pmu.cntval_bits);
>  	pr_info("... generic registers:      %d\n",     x86_pmu.num_counters);
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c index
> 4244bed..a5bc4e4 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3160,6 +3160,19 @@ static int intel_pmu_cpu_prepare(int cpu)
>  	return -ENOMEM;
>  }
> 
> +static void flip_smm_bit(void *data)
> +{
> +	bool set = *(int *)data;
> +
> +	if (set) {
> +		msr_set_bit(MSR_IA32_DEBUGCTLMSR,
> +			    DEBUGCTLMSR_FREEZE_IN_SMM_BIT);
> +	} else {
> +		msr_clear_bit(MSR_IA32_DEBUGCTLMSR,
> +			      DEBUGCTLMSR_FREEZE_IN_SMM_BIT);
> +	}
> +}
> +
>  static void intel_pmu_cpu_starting(int cpu)  {
>  	struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu); @@ -
> 3174,6 +3187,8 @@ static void intel_pmu_cpu_starting(int cpu)
> 
>  	cpuc->lbr_sel = NULL;
> 
> +	flip_smm_bit(&x86_pmu.attr_freeze_on_smi);
> +
>  	if (!cpuc->shared_regs)
>  		return;
> 
> @@ -3595,6 +3610,52 @@ static struct attribute *hsw_events_attrs[] = {
>  	NULL
>  };
> 
> +static ssize_t freeze_on_smi_show(struct device *cdev,
> +				  struct device_attribute *attr,
> +				  char *buf)
> +{
> +	return sprintf(buf, "%d\n", x86_pmu.attr_freeze_on_smi); }
> +
> +static DEFINE_MUTEX(freeze_on_smi_mutex);
> +
> +static ssize_t freeze_on_smi_store(struct device *cdev,
> +				   struct device_attribute *attr,
> +				   const char *buf, size_t count)
> +{
> +	unsigned long val;
> +	ssize_t ret;
> +
> +	ret = kstrtoul(buf, 0, &val);
> +	if (ret)
> +		return ret;
> +
> +	if (val > 1)
> +		return -EINVAL;
> +
> +	mutex_lock(&freeze_on_smi_mutex);
> +
> +	if (x86_pmu.attr_freeze_on_smi == val)
> +		goto done;
> +
> +	x86_pmu.attr_freeze_on_smi = val;
> +
> +	get_online_cpus();
> +	on_each_cpu(flip_smm_bit, &val, 1);
> +	put_online_cpus();
> +done:
> +	mutex_unlock(&freeze_on_smi_mutex);
> +
> +	return count;
> +}
> +
> +static DEVICE_ATTR_RW(freeze_on_smi);
> +
> +static struct attribute *intel_pmu_attrs[] = {
> +	&dev_attr_freeze_on_smi.attr,
> +	NULL,
> +};
> +
>  __init int intel_pmu_init(void)
>  {
>  	union cpuid10_edx edx;
> @@ -3641,6 +3702,8 @@ __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:
> diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
> index bcbb1d2..110cb9b0 100644
> --- a/arch/x86/events/perf_event.h
> +++ b/arch/x86/events/perf_event.h
> @@ -561,6 +561,9 @@ struct x86_pmu {
>  	ssize_t		(*events_sysfs_show)(char *page, u64 config);
>  	struct attribute **cpu_events;
> 
> +	int		attr_freeze_on_smi;
> +	struct attribute **attrs;
> +
>  	/*
>  	 * CPU Hotplug hooks
>  	 */
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-
> index.h
> index d8b5f8a..0572f91 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -134,6 +134,8 @@
>  #define DEBUGCTLMSR_BTS_OFF_OS		(1UL <<  9)
>  #define DEBUGCTLMSR_BTS_OFF_USR		(1UL << 10)
>  #define DEBUGCTLMSR_FREEZE_LBRS_ON_PMI	(1UL << 11)
> +#define DEBUGCTLMSR_FREEZE_IN_SMM_BIT	14
> +#define DEBUGCTLMSR_FREEZE_IN_SMM	(1UL <<
> DEBUGCTLMSR_FREEZE_IN_SMM_BIT)
> 
>  #define MSR_PEBS_FRONTEND		0x000003f7
> 
> --
> 2.7.4