[RFC PATCH 0/4] PMU partitioning driver support

[Colton Lewis]

This series introduces support in the ARM PMUv3 driver for
partitioning PMU counters into two separate ranges by taking advantage
of the MDCR_EL2.HPMN register field.

The advantage of a partitioned PMU would be to allow KVM guests direct
access to a subset of PMU functionality, greatly reducing the overhead
of performance monitoring in guests.

While this series could be accepted on its own merits, practically
there is a lot more to be done before it will be fully useful, so I'm
sending as an RFC for now.

This patch is based on v6.13-rc7. It needs a small additional change
after Oliver's Debug cleanups series going into 6.14, specifically
this patch [1], because it changes kvm_arm_setup_mdcr_el2() to
initialize HPMN from a cached value read early in the boot process
instead of reading from the register. The only sensible way I can see
to deal with this is returning to reading the register.

[1] https://lore.kernel.org/kvmarm/20241219224116.3941496-3-oliver.upton@linux.dev/

Colton Lewis (4):
  perf: arm_pmuv3: Introduce module param to partition the PMU
  KVM: arm64: Make guests see only counters they can access
  perf: arm_pmuv3: Generalize counter bitmasks
  perf: arm_pmuv3: Keep out of guest counter partition

 arch/arm/include/asm/arm_pmuv3.h              |  10 ++
 arch/arm64/include/asm/arm_pmuv3.h            |  10 ++
 arch/arm64/kvm/pmu-emul.c                     |   8 +-
 drivers/perf/arm_pmuv3.c                      | 113 ++++++++++++++++--
 include/linux/perf/arm_pmu.h                  |   2 +
 include/linux/perf/arm_pmuv3.h                |  34 +++++-
 .../kvm/aarch64/vpmu_counter_access.c         |   2 +-
 7 files changed, 160 insertions(+), 19 deletions(-)


base-commit: 5bc55a333a2f7316b58edc7573e8e893f7acb532
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2.48.1.262.g85cc9f2d1e-goog