Re: [PATCH V2 6/7] arm64/perf: Add BRBE driver

On 9/13/22 16:09, James Clark wrote:

On 08/09/2022 06:10, Anshuman Khandual wrote:

quoted

This adds a BRBE driver which implements all the required helper functions
for struct arm_pmu. Following functions are defined by this driver which
will configure, enable, capture, reset and disable BRBE buffer HW as and
when requested via perf branch stack sampling framework.

- arm64_pmu_brbe_filter()
- arm64_pmu_brbe_enable()
- arm64_pmu_brbe_disable()
- arm64_pmu_brbe_read()
- arm64_pmu_brbe_probe()
- arm64_pmu_brbe_reset()
- arm64_pmu_brbe_supported()

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-perf-users@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <redacted>
---
 arch/arm64/kernel/perf_event.c |   8 +-
 drivers/perf/Kconfig           |  11 +
 drivers/perf/Makefile          |   1 +
 drivers/perf/arm_pmu_brbe.c    | 448 +++++++++++++++++++++++++++++++++
 drivers/perf/arm_pmu_brbe.h    | 259 +++++++++++++++++++
 include/linux/perf/arm_pmu.h   |  20 ++
 6 files changed, 746 insertions(+), 1 deletion(-)
 create mode 100644 drivers/perf/arm_pmu_brbe.c
 create mode 100644 drivers/perf/arm_pmu_brbe.h

[...]

quoted

+
+static int brbe_fetch_perf_priv(u64 brbinf)
+{
+       int brbe_el = brbe_fetch_el(brbinf);
+
+       switch (brbe_el) {
+       case BRBINF_EL_EL0:
+               return PERF_BR_PRIV_USER;
+       case BRBINF_EL_EL1:
+               return PERF_BR_PRIV_KERNEL;
+       case BRBINF_EL_EL2:
+               if (is_kernel_in_hyp_mode())
+                       return PERF_BR_PRIV_KERNEL;
+               return PERF_BR_PRIV_HV;
+       default:
+               pr_warn("unknown branch privilege captured\n");
+               return -1;

On V1 you said that you would change this to PERF_BR_PRIV_UNKNOWN, looks
like that was dropped. Unless it didn't work out?

Seems like it just got dropped unintentionally. Yes, PERF_BR_PRIV_UNKNOWN
can be returned here instead of "-1", similar to brbe_fetch_perf_type()
which returns PERF_BR_UNKNOWN.

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