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Subject[PATCH V5] arm64: perf: Make exporting of pmu events configurable
Date
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@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,
+ },
{ }
};

--
2.7.4
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