linux-kernel - [PATCH V8 3/6] arm64/perf: Add branch stack support in struct arm

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Message-Id: <20230123125956.1350336-4-anshuman.khandual@arm.com>
Date:   Mon, 23 Jan 2023 18:29:53 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        will@...nel.org, catalin.marinas@....com, mark.rutland@....com
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        Mark Brown <broonie@...nel.org>,
        James Clark <james.clark@....com>,
        Rob Herring <robh@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Suzuki Poulose <suzuki.poulose@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-perf-users@...r.kernel.org
Subject: [PATCH V8 3/6] arm64/perf: Add branch stack support in struct arm_pmu

This updates 'struct arm_pmu' for branch stack sampling support later. This
adds a new 'features' element in the structure to track supported features,
and another 'private' element to encapsulate implementation attributes on a
given 'struct arm_pmu'. These updates here will help in tracking any branch
stack sampling support, which is being added later. This also adds a helper
arm_pmu_branch_stack_supported().

This also enables perf branch stack sampling event on all 'struct arm pmu',
supporting the feature but after removing the current gate that blocks such
events unconditionally in armpmu_event_init(). Instead a quick probe can be
initiated via arm_pmu_branch_stack_supported() to ascertain the support.

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
 drivers/perf/arm_pmu.c       |  3 +--
 include/linux/perf/arm_pmu.h | 12 +++++++++++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 14a3ed3bdb0b..a85b2d67022e 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -510,8 +510,7 @@ static int armpmu_event_init(struct perf_event *event)
 		!cpumask_test_cpu(event->cpu, &armpmu->supported_cpus))
 		return -ENOENT;
 
-	/* does not support taken branch sampling */
-	if (has_branch_stack(event))
+	if (has_branch_stack(event) && !arm_pmu_branch_stack_supported(armpmu))
 		return -EOPNOTSUPP;
 
 	return __hw_perf_event_init(event);
diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 2a9d07cee927..78cb1c895ab9 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h
@@ -103,7 +103,9 @@ struct arm_pmu {
 	bool		(*filter)(struct pmu *pmu, int cpu);
 	void		(*sched_task)(struct perf_event_pmu_context *pmu_ctx, bool sched_in);
 	int		num_events;
-	bool		secure_access; /* 32-bit ARM only */
+	unsigned int	secure_access	: 1, /* 32-bit ARM only */
+			has_branch_stack: 1, /* 64-bit ARM only */
+			reserved	: 30;
 #define ARMV8_PMUV3_MAX_COMMON_EVENTS		0x40
 	DECLARE_BITMAP(pmceid_bitmap, ARMV8_PMUV3_MAX_COMMON_EVENTS);
 #define ARMV8_PMUV3_EXT_COMMON_EVENT_BASE	0x4000
@@ -119,8 +121,16 @@ struct arm_pmu {
 
 	/* Only to be used by ACPI probing code */
 	unsigned long acpi_cpuid;
+
+	/* Implementation specific attributes */
+	void		*private;
 };
 
+static inline bool arm_pmu_branch_stack_supported(struct arm_pmu *armpmu)
+{
+	return armpmu->has_branch_stack;
+}
+
 #define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))
 
 u64 armpmu_event_update(struct perf_event *event);
-- 
2.25.1