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Message-ID: <d412031a-cdfa-4983-8702-1e1bb93d5641@linaro.org>
Date: Thu, 29 May 2025 10:48:20 +0100
From: James Clark <james.clark@...aro.org>
To: "Rob Herring (Arm)" <robh@...nel.org>, Will Deacon <will@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
kvmarm@...ts.linux.dev, Mark Brown <broonie@...nel.org>,
Dave Martin <Dave.Martin@....com>, Mark Rutland <mark.rutland@....com>,
Catalin Marinas <catalin.marinas@....com>, Jonathan Corbet <corbet@....net>,
Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>,
Zenghui Yu <yuzenghui@...wei.com>,
Anshuman Khandual <anshuman.khandual@....com>, Leo Yan <leo.yan@....com>
Subject: Re: [PATCH v22 0/5] arm64/perf: Enable branch stack sampling
On 20/05/2025 11:27 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 later versions have
> been reworked quite a bit by Mark and myself. The bulk of those changes
> are in patch 5.
>
> A git branch is here[2].
>
> [1] https://developer.arm.com/documentation/ddi0487/latest/
> [2] git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git arm/brbe-v22
>
> Changes in v22:
> - New patch reworking the labels in el2_setup.h
> - Move branch stack disabling after armpmu_stop() in armpmu_del()
> - Fix branch_records_alloc() to work on heterogeneous systems
> - Make setting .sched_task function ptr conditional on BRBE support
> - Reword booting.rst section name (s/feature/the/) and move next to
> other PMU related features instead of in the middle of SME features.
> - Drop setting SYS_BRBCR_EL1
> - Drop CONFIG_ARM64_BRBE ifdef
> - Rework initialization of HFGITR_EL2
>
> v21:
> - https://lore.kernel.org/r/20250407-arm-brbe-v19-v21-0-ff187ff6c928@kernel.org
> - Drop clean-up patches 1-7 already applied
> - Rebase on v6.15-rc1
>
> v20:
> - https://lore.kernel.org/r/20250218-arm-brbe-v19-v20-0-4e9922fc2e8e@kernel.org
> - 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
>
> v19:
> - https://lore.kernel.org/all/20250202-arm-brbe-v19-v19-0-1c1300802385@kernel.org/
> - Drop saving of branch records when task scheduled out (Mark). Make
> sched_task() callback actually get called. Enabling requires a call
> to perf_sched_cb_inc(). So the saving of branch records never
> happened.
> - Got rid of added armpmu ops. All BRBE support is contained within
> pmuv3 code.
> - Fix freeze on overflow for VHE
> - The cycle counter doesn't freeze BRBE on overflow, so avoid assigning
> it when BRBE is enabled.
> - Drop all the Arm specific exception branches. Not a clear need for
> them.
> - Fix handling of branch 'cycles' reading. CC field is
> mantissa/exponent, not an integer.
> - Rework s/w filtering to better match h/w filtering
> - Reject events with disjoint event filter and branch filter or with
> exclude_host set
> - Dropped perf test patch which has been applied for 6.14
> - Dropped patch "KVM: arm64: Explicitly handle BRBE traps as UNDEFINED"
> which has been applied for 6.14
>
> v18:
> - https://lore.kernel.org/all/20240613061731.3109448-1-anshuman.khandual@arm.com/
>
> For v1-v17, see the above link. Not going to duplicate it all here...
>
> Signed-off-by: "Rob Herring (Arm)" <robh@...nel.org>
> ---
> ---
> Anshuman Khandual (4):
> arm64/sysreg: Add BRBE registers and fields
> arm64: el2_setup.h: Make __init_el2_fgt labels consistent, again
> arm64: Handle BRBE booting requirements
> KVM: arm64: nvhe: Disable branch generation in nVHE guests
>
> Rob Herring (Arm) (1):
> perf: arm_pmuv3: Add support for the Branch Record Buffer Extension (BRBE)
>
> Documentation/arch/arm64/booting.rst | 21 +
> arch/arm64/include/asm/el2_setup.h | 81 +++-
> arch/arm64/include/asm/kvm_host.h | 2 +
> arch/arm64/include/asm/sysreg.h | 17 +-
> arch/arm64/kvm/debug.c | 4 +
> arch/arm64/kvm/hyp/nvhe/debug-sr.c | 32 ++
> arch/arm64/kvm/hyp/nvhe/switch.c | 2 +-
> arch/arm64/tools/sysreg | 132 ++++++
> drivers/perf/Kconfig | 11 +
> drivers/perf/Makefile | 1 +
> drivers/perf/arm_brbe.c | 802 +++++++++++++++++++++++++++++++++++
> drivers/perf/arm_brbe.h | 47 ++
> drivers/perf/arm_pmu.c | 16 +-
> drivers/perf/arm_pmuv3.c | 125 +++++-
> include/linux/perf/arm_pmu.h | 8 +
> 15 files changed, 1276 insertions(+), 25 deletions(-)
> ---
> base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
> change-id: 20250129-arm-brbe-v19-24d5d9e5e623
>
> Best regards,
Tested-by: James Clark <james.clark@...aro.org>
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