[RFC,v3,0/8] PMU partitioning driver support

Message

Colton Lewis Feb. 13, 2025, 6:03 p.m. UTC

This series introduces support in the KVM and 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 feature 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.

v3:
* Include cpucap definition for FEAT_HPMN0 to allow for setting HPMN
  to 0

* Include PMU header cleanup provided by Marc [1] with some minor
  changes so compilation works

* Pull functions out of pmu-emul.c that aren't specific to the
  emulated PMU. This and the previous item aren't strictly
  needed but they provide a nicer starting point.

* As suggested by Oliver, start a file for partitioned PMU functions
  and move the reserved_host_counters parameter and MDCR handling into
  KVM so the driver does not have to know about it and we need fewer
  hacks to keep the driver working on 32-bit ARM. This was not a
  complete separation because the driver still needs to start and stop
  the host counters all at once and needs to toggle MDCR_EL2.HPME to
  do that. Introduce kvm_pmu_host_counters_{enable,disable}()
  functions to handle this and define them as no ops on 32-bit ARM.

* As suggested by Oliver, don't limit PMCR.N on emulated PMU. This
  value will be read correctly when the right traps are disabled to
  use the partitioned PMU

v2:
https://lore.kernel.org/kvm/[e-mail]/

v1:
https://lore.kernel.org/kvm/[e-mail]/

[1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/pmu-includes

Colton Lewis (7):
  arm64: cpufeature: Add cap for HPMN0
  arm64: Generate sign macro for sysreg Enums
  KVM: arm64: Reorganize PMU functions
  KVM: arm64: Introduce module param to partition the PMU
  perf: arm_pmuv3: Generalize counter bitmasks
  perf: arm_pmuv3: Keep out of guest counter partition
  KVM: arm64: selftests: Reword selftests error

Marc Zyngier (1):
  KVM: arm64: Cleanup PMU includes

 arch/arm/include/asm/arm_pmuv3.h              |   2 +
 arch/arm64/include/asm/arm_pmuv3.h            |   2 +-
 arch/arm64/include/asm/kvm_host.h             | 199 +++++++-
 arch/arm64/include/asm/kvm_pmu.h              |  47 ++
 arch/arm64/kernel/cpufeature.c                |   8 +
 arch/arm64/kvm/Makefile                       |   2 +-
 arch/arm64/kvm/arm.c                          |   1 -
 arch/arm64/kvm/debug.c                        |  10 +-
 arch/arm64/kvm/hyp/include/hyp/switch.h       |   1 +
 arch/arm64/kvm/pmu-emul.c                     | 464 +-----------------
 arch/arm64/kvm/pmu-part.c                     |  63 +++
 arch/arm64/kvm/pmu.c                          | 454 +++++++++++++++++
 arch/arm64/kvm/sys_regs.c                     |   2 +
 arch/arm64/tools/cpucaps                      |   1 +
 arch/arm64/tools/gen-sysreg.awk               |   1 +
 arch/arm64/tools/sysreg                       |   6 +-
 drivers/perf/arm_pmuv3.c                      |  73 ++-
 include/kvm/arm_pmu.h                         | 204 --------
 include/linux/perf/arm_pmu.h                  |  16 +-
 include/linux/perf/arm_pmuv3.h                |  27 +-
 .../selftests/kvm/arm64/vpmu_counter_access.c |   2 +-
 virt/kvm/kvm_main.c                           |   1 +
 22 files changed, 882 insertions(+), 704 deletions(-)
 create mode 100644 arch/arm64/include/asm/kvm_pmu.h
 create mode 100644 arch/arm64/kvm/pmu-part.c
 delete mode 100644 include/kvm/arm_pmu.h


base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
--
2.48.1.601.g30ceb7b040-goog