linux-kernel - [PATCH 3/6] arm64: pmu: Add function implementation to update event index in userpage.

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Date:   Thu, 16 May 2019 14:21:45 +0100
From:   Raphael Gault <raphael.gault@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     mingo@...hat.com, peterz@...radead.org, catalin.marinas@....com,
        will.deacon@....com, acme@...nel.org, mark.rutland@....com,
        Raphael Gault <raphael.gault@....com>
Subject: [PATCH 3/6] arm64: pmu: Add function implementation to update event index in userpage.

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.

Signed-off-by: Raphael Gault <raphael.gault@....com>
---
 arch/arm64/kernel/perf_event.c |  4 ++++
 drivers/perf/arm_pmu.c         | 10 ++++++++++
 include/linux/perf/arm_pmu.h   |  2 ++
 3 files changed, 16 insertions(+)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 6164d389eed6..e6316f99f66b 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -890,6 +890,8 @@ static int __armv8_pmuv3_map_event(struct perf_event *event,
 	if (armv8pmu_event_is_64bit(event))
 		event->hw.flags |= ARMPMU_EVT_64BIT;
 
+	event->hw.flags |= ARMPMU_EL0_RD_CNTR;
+
 	/* Only expose micro/arch events supported by this PMU */
 	if ((hw_event_id > 0) && (hw_event_id < ARMV8_PMUV3_MAX_COMMON_EVENTS)
 	    && test_bit(hw_event_id, armpmu->pmceid_bitmap)) {
@@ -1188,6 +1190,8 @@ void arch_perf_update_userpage(struct perf_event *event,
 	 */
 	freq = arch_timer_get_rate();
 	userpg->cap_user_time = 1;
+	userpg->cap_user_rdpmc =
+		!!(event->hw.flags & ARMPMU_EL0_RD_CNTR);
 
 	clocks_calc_mult_shift(&userpg->time_mult, &shift, freq,
 			NSEC_PER_SEC, 0);
diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index eec75b97e7ea..3f4c2ec7ff89 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -777,6 +777,15 @@ static void cpu_pmu_destroy(struct arm_pmu *cpu_pmu)
 					    &cpu_pmu->node);
 }
 
+
+static int armpmu_event_idx(struct perf_event *event)
+{
+	if (!(event->hw.flags & ARMPMU_EL0_RD_CNTR))
+		return 0;
+
+	return event->hw.idx;
+}
+
 static struct arm_pmu *__armpmu_alloc(gfp_t flags)
 {
 	struct arm_pmu *pmu;
@@ -803,6 +812,7 @@ static struct arm_pmu *__armpmu_alloc(gfp_t flags)
 		.start		= armpmu_start,
 		.stop		= armpmu_stop,
 		.read		= armpmu_read,
+		.event_idx	= armpmu_event_idx,
 		.filter_match	= armpmu_filter_match,
 		.attr_groups	= pmu->attr_groups,
 		/*
diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 4641e850b204..3bef390c1069 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h
@@ -30,6 +30,8 @@
  */
 /* 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		0xFFFF
 #define C(_x)				PERF_COUNT_HW_CACHE_##_x
-- 
2.17.1