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arm64: perf: Add userspace counter access disable switch

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Like x86, some users may want to disable userspace PMU counter
altogether. Add a sysctl 'perf_user_access' file to control userspace
counter access. The default is '0' which is disabled. Writing '1'
enables access.

Note that x86 supports globally enabling user access by writing '2' to
/sys/bus/event_source/devices/cpu/rdpmc. As there's not existing
userspace support to worry about, this shouldn't be necessary for Arm.
It could be added later if the need arises.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-perf-users@vger.kernel.org
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211208201124.310740-4-robh@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Rob Herring 2021-12-08 14:11:22 -06:00 committed by Will Deacon
parent 82ff0c022d
commit e201260081
2 changed files with 28 additions and 0 deletions
Documentation/admin-guide/sysctl
kernel.rst
arch/arm64/kernel
perf_event.c

11
Documentation/admin-guide/sysctl/kernel.rst

@ -905,6 +905,17 @@ enabled, otherwise writing to this file will return ``-EBUSY``.
The default value is 8. The default value is 8.
perf_user_access (arm64 only)
=================================
Controls user space access for reading perf event counters. When set to 1,
user space can read performance monitor counter registers directly.
The default value is 0 (access disabled).
See Documentation/arm64/perf.rst for more information.
pid_max pid_max
======= =======

17
arch/arm64/kernel/perf_event.c

@ -286,6 +286,8 @@ static const struct attribute_group armv8_pmuv3_events_attr_group = {
PMU_FORMAT_ATTR(event, "config:0-15"); PMU_FORMAT_ATTR(event, "config:0-15");
PMU_FORMAT_ATTR(long, "config1:0"); PMU_FORMAT_ATTR(long, "config1:0");
static int sysctl_perf_user_access __read_mostly;
static inline bool armv8pmu_event_is_64bit(struct perf_event *event) static inline bool armv8pmu_event_is_64bit(struct perf_event *event)
{ {
return event->attr.config1 & 0x1; return event->attr.config1 & 0x1;
@ -1104,6 +1106,19 @@ static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu)
return probe.present ? 0 : -ENODEV; return probe.present ? 0 : -ENODEV;
} }
static struct ctl_table armv8_pmu_sysctl_table[] = {
{
.procname = "perf_user_access",
.data = &sysctl_perf_user_access,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
{ }
};
static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name, static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name,
int (*map_event)(struct perf_event *event), int (*map_event)(struct perf_event *event),
const struct attribute_group *events, const struct attribute_group *events,
@ -1136,6 +1151,8 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name,
cpu_pmu->attr_groups[ARMPMU_ATTR_GROUP_CAPS] = caps ? cpu_pmu->attr_groups[ARMPMU_ATTR_GROUP_CAPS] = caps ?
caps : &armv8_pmuv3_caps_attr_group; caps : &armv8_pmuv3_caps_attr_group;
register_sysctl("kernel", armv8_pmu_sysctl_table);
return 0; return 0;
} }