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

[James Clark]

On 08/09/2022 06:10, Anshuman Khandual wrote:
> 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@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-perf-users@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
>  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
> 
[...]
> +
> +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?