[PATCH v20 00/11] arm64/perf: Enable branch stack sampling

[James Clark]

On 18/02/2025 8:39 pm, Rob Herring (Arm) wrote:
> This series enables perf branch stack sampling support on arm64 via a
> v9.2 arch feature called Branch Record Buffer Extension (BRBE). Details
> on BRBE can be found in the Arm ARM[1] chapter D18.
> 
> I've picked up this series from Anshuman. v19 and v20 versions have been
> reworked quite a bit by Mark and myself. The bulk of those changes are
> in patch 11.
> 
> Patches 1-7 are new clean-ups/prep which stand on their own. They
> were previously posted here[2]. Please pick them up if there's no issues
> with them.
> 
> Patches 8-11 add BRBE support with the actual support in patch 11.
> 
> A git branch is here[3].
> 
> [1] https://developer.arm.com/documentation/ddi0487/latest/
> [2] https://lore.kernel.org/all/20250107-arm-pmu-cleanups-v1-v1-0-313951346a25@kernel.org/
> [3] git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git arm/brbe-v20
> 
> v20:
>   - Added back some of the arm64 specific exception types. The x86 IRQ
>     branches also include other exceptions like page faults. On arm64, we
>     can distinguish the exception types, so we do. Also, to better
>     align with x86, we convert 'call' branches which are user to kernel
>     to 'syscall'.
>   - Only enable exceptions and exception returns if recording kernel
>     branches (matching x86)
>   - Drop requiring event and branch privileges to match
>   - Add "branches" caps sysfs attribute like x86
>   - Reword comment about FZP and MDCR_EL2.HPMN interaction
>   - Rework BRBE invalidation to avoid invalidating in interrupt handler
>     when no handled events capture the branch stack (i.e. when there are
>     multiple users).
>   - Also clear BRBCR_ELx bits in brbe_disable(). This is for KVM nVHE
>     checks if BRBE is enabled.
>   - Document that MDCR_EL3.SBRBE can be 0b01 also
> 

Tested-by: James Clark <james.clark at linaro.org>