[PATCH V5] arm64: perf: Make exporting of pmu events configurable

[Srinivasarao Pathipati]

Hi Will / Robin ,

Could you please review this change.

On 5/23/2022 5:19 PM, Srinivasarao Pathipati wrote:
> The PMU export bit (PMCR_EL0.X) is getting reset during pmu reset,
> Make is configurable using sysctls to enable/disable at runtime.
> It can also be enabled at early bootup with kernel arguments.
>
> Signed-off-by: Srinivasarao Pathipati <quic_c_spathi at quicinc.com>
> ---
> Changes since V4:
> 	- Registering sysctls dynamically for only arm64 as suggested by Will
> 	- Not removed the code to configure with kernel parameters
> 	  as the sysctl's kernel parameter(sysctl.kernel.export_pmu_events)
> 	  is not working at early bootup. pmu_reset() getting called before
> 	  sysctl's kernel parameter is set.
> Changes since V3:
> 	- export bit is now configurable with sysctl
> 	- enabling export bit on reset instead of retaining
>
> Changes since V2:
> 	Done below changes as per Will's comments
> 	- enabling pmcr_x now configurable with kernel parameters and
> 	  by default it is disabled.
> 	
> Changes since V1:
> 	- Preserving only PMCR_X bit as per Robin Murphy's comment.
>
> ---
>   Documentation/admin-guide/kernel-parameters.txt |  5 +++++
>   Documentation/admin-guide/sysctl/kernel.rst     |  9 +++++++++
>   arch/arm64/kernel/perf_event.c                  | 24 ++++++++++++++++++++++++
>   3 files changed, 38 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index de3da15..2bf1187 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5150,6 +5150,11 @@
>   			Useful for devices that are detected asynchronously
>   			(e.g. USB and MMC devices).
>   
> +	export_pmu_events
> +			[KNL,ARM64] Sets the PMU export bit (PMCR_EL0.X), which enables
> +			the exporting of events over an IMPLEMENTATION DEFINED PMU event
> +			export bus to another device.
> +
>   	retain_initrd	[RAM] Keep initrd memory after extraction
>   
>   	rfkill.default_state=
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index ddccd10..db42d4c 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -892,6 +892,15 @@ The default value is 0 (access disabled).
>   
>   See Documentation/arm64/perf.rst for more information.
>   
> +export_pmu_events (arm64 only)
> +==============================
> +Controls the PMU export bit (PMCR_EL0.X), which enables the exporting of
> +events over an IMPLEMENTATION DEFINED PMU event export bus to another device.
> +
> +0: disables exporting of events (default).
> +
> +1: enables exporting of events.
> +
>   
>   pid_max
>   =======
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index cb69ff1..d93e7c4 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -298,6 +298,7 @@ PMU_FORMAT_ATTR(long, "config1:0");
>   PMU_FORMAT_ATTR(rdpmc, "config1:1");
>   
>   static int sysctl_perf_user_access __read_mostly;
> +static int sysctl_export_pmu_events __read_mostly;
>   
>   static inline bool armv8pmu_event_is_64bit(struct perf_event *event)
>   {
> @@ -1025,6 +1026,17 @@ static int armv8pmu_filter_match(struct perf_event *event)
>   	return evtype != ARMV8_PMUV3_PERFCTR_CHAIN;
>   }
>   
> +static int __init export_pmu_events(char *str)
> +{
> +	/* Enable exporting of pmu events at early bootup with kernel
> +	 * arguments.
> +	 */
> +	sysctl_export_pmu_events = 1;
> +	return 0;
> +}
> +
> +early_param("export_pmu_events", export_pmu_events);
> +
>   static void armv8pmu_reset(void *info)
>   {
>   	struct arm_pmu *cpu_pmu = (struct arm_pmu *)info;
> @@ -1047,6 +1059,9 @@ static void armv8pmu_reset(void *info)
>   	if (armv8pmu_has_long_event(cpu_pmu))
>   		pmcr |= ARMV8_PMU_PMCR_LP;
>   
> +	if (sysctl_export_pmu_events)
> +		pmcr |= ARMV8_PMU_PMCR_X;
> +
>   	armv8pmu_pmcr_write(pmcr);
>   }
>   
> @@ -1221,6 +1236,15 @@ static struct ctl_table armv8_pmu_sysctl_table[] = {
>   		.extra1		= SYSCTL_ZERO,
>   		.extra2		= SYSCTL_ONE,
>   	},
> +	{
> +		.procname       = "export_pmu_events",
> +		.data           = &sysctl_export_pmu_events,
> +		.maxlen         = sizeof(unsigned int),
> +		.mode           = 0644,
> +		.proc_handler   = proc_dointvec_minmax,
> +		.extra1         = SYSCTL_ZERO,
> +		.extra2         = SYSCTL_ONE,
> +	},
>   	{ }
>   };
>