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/20250208020111.2068239-1-coltonlewis@google.com/
v1: https://lore.kernel.org/kvm/20250127222031.3078945-1-coltonlewis@google.com/
[1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h...
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