From: Raphael Gault
In order to be able to access the counter directly for userspace,
we need to provide the index of the counter using the userpage.
We thus need to override the event_idx function to retrieve and
convert the perf_event index to armv8 hardware index.
Since the arm_pmu driver can be used by any implementation, even
if not armv8, two components play a role into making sure the
behaviour is correct and consistent with the PMU capabilities:
* the ARMPMU_EL0_RD_CNTR flag which denotes the capability to access
counter from userspace.
* the event_idx call back, which is implemented and initialized by
the PMU implementation: if no callback is provided, the default
behaviour applies, returning 0 as index value.
Signed-off-by: Raphael Gault
Signed-off-by: Rob Herring
---
arch/arm64/kernel/perf_event.c | 18 ++
include/linux/perf/arm_pmu.h | 2 ++
2 files changed, 20 insertions(+)
diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 4658fcf88c2b..387838496955 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -871,6 +871,22 @@ static void armv8pmu_clear_event_idx(struct pmu_hw_events
*cpuc,
clear_bit(idx - 1, cpuc->used_mask);
}
+static int armv8pmu_access_event_idx(struct perf_event *event)
+{
+ if (!(event->hw.flags & ARMPMU_EL0_RD_CNTR))
+ return 0;
+
+ /*
+* We remap the cycle counter index to 32 to
+* match the offset applied to the rest of
+* the counter indices.
+*/
+ if (event->hw.idx == ARMV8_IDX_CYCLE_COUNTER)
+ return 32;
+
+ return event->hw.idx;
+}
+
/*
* Add an event filter to a given event.
*/
@@ -1098,6 +1114,8 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char
*name,
cpu_pmu->set_event_filter = armv8pmu_set_event_filter;
cpu_pmu->filter_match = armv8pmu_filter_match;
+ cpu_pmu->pmu.event_idx = armv8pmu_access_event_idx;
+
cpu_pmu->name = name;
cpu_pmu->map_event = map_event;
cpu_pmu->attr_groups[ARMPMU_ATTR_GROUP_EVENTS] = events ?
diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 505480217cf1..d29aa981d989 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h
@@ -26,6 +26,8 @@
*/
/* Event uses a 64bit counter */
#define ARMPMU_EVT_64BIT 1
+/* Allow access to hardware counter from userspace */
+#define ARMPMU_EL0_RD_CNTR 2
#define HW_OP_UNSUPPORTED 0x
#define C(_x) PERF_COUNT_HW_CACHE_##_x
--
2.27.0
