[RFC PATCH 0/3] arm64: expose CPU prefetch and cache modulation controls

[KobaK <kobak@nvidia.com>]

From: Koba Ko <kobak@nvidia.com>

This series adds CONFIG_ARM64_CPUMOD, a default-off arm64 interface for
controlled performance characterization of selected implementation-defined
CPU prefetch and cache-management fields. It exposes a small set of named,
per-CPU attributes under the path below, with writable control fields
range-checked before register state is changed:

  /sys/devices/system/cpu/cpuN/cpumod/

The directory is created for online CPUs whose MIDR matches a recognized
Grace or Vera profile, with common and profile-specific attributes selected
for that CPU. Register accesses execute on the CPU that owns the sysfs
instance, and CPU hotplug creates or removes the per-CPU subtree as the CPU
transitions online or offline. Unsupported CPU profiles are skipped without
blocking module load or CPU hotplug.

The implementation keeps each dynamically allocated kobject in a private
per-CPU pointer, avoiding use of the CPU device's shared driver-data slot.
The documentation defines the ABI, firmware prerequisite, and hotplug
lifecycle. The kselftest validates profile-specific layout, unsupported-CPU
skipping, decimal affected_cpus reporting, value validation, optional
writes, all-online-CPU coverage, and cleanup.

The controls require firmware to permit EL1 access to the relevant
implementation control registers. This is an RFC interface for controlled
evaluation, not a general raw-register or production-default tuning ABI.

Compile and static verification passed. DUT runtime validation was not run.

Koba Ko (3):
  arm64: add CPU prefetch and cache modulation sysfs interface
  Documentation/arch/arm64: document arm_cpumod
  selftests: arm64: add arm_cpumod kselftest

 Documentation/arch/arm64/arm-cpumod.rst       |  89 +++
 Documentation/arch/arm64/index.rst            |   1 +
 arch/arm64/Kconfig                            |  17 +
 arch/arm64/kernel/Makefile                    |   1 +
 arch/arm64/kernel/arm_cpumod.c                | 471 ++++++++++++++++
 arch/arm64/kernel/arm_cpumod_internal.h       | 113 ++++
 tools/testing/selftests/arm64/Makefile        |   2 +-
 .../selftests/arm64/arm_cpumod/Makefile       |   5 +
 .../selftests/arm64/arm_cpumod/arm_cpumod.sh  | 526 ++++++++++++++++++
 9 files changed, 1224 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/arch/arm64/arm-cpumod.rst
 create mode 100644 arch/arm64/kernel/arm_cpumod.c
 create mode 100644 arch/arm64/kernel/arm_cpumod_internal.h
 create mode 100644 tools/testing/selftests/arm64/arm_cpumod/Makefile
 create mode 100755 tools/testing/selftests/arm64/arm_cpumod/arm_cpumod.sh

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2.43.0