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 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.
v2: * Rebase to v6.14-rc1, and take into account Oliver's debug cleanup changing some KVM handling of MDCR_EL2.
* Reorder patches to put related things closer together for easier reading.
* Ensure driver compiles for 32-bit ARM by defining 32-bit access to MDCR_EL2 correctly, which is called HDCR there. These will not be called due to the below requirement for VHE mode but a functionally correct definition seemed preferable to making it a no op.
* Rename parameter to reserved_host_counters to better reflect underlying hardware semantics and ensure host counters are easier to preserve.
* Document parameter with MODULE_PARM_DESC
* Restrict partitioning to VHE mode only. Using HPMN restricts the host counters to EL2 access only. Trying to make this work for the driver running at EL1 would require hypercalls for every access of those registers and a lot of additional handling at the KVM level. This would defeat the whole purpose of having the feature at all. Define has_vhe() on 32-bit arm to always return false.
* While Rob asked about making the parameter configurable at run time rather than boot time through sysfs, that is potentially very tricky because it is only safe to reprogram HPMN when we are certain no one, host or guest, is using any counters that might change ownership. If this is determined to be worthwhile, it should come after getting the core infrastructure right.
* While Marc asked about reusing the sysreg masks instead of redefining them for MDCR_EL2, that doesn't work because sysreg masks are only defined for arm64. I'm not sure how to avoid the duplication.
* Wrap code for determining if a counter index belongs to the host or guest partition in functions
* Typo fixes and additional testing
v1: https://lore.kernel.org/kvm/20250127222031.3078945-1-coltonlewis@google.com/
Colton Lewis (4): perf: arm_pmuv3: Generalize counter bitmasks perf: arm_pmuv3: Introduce module param to partition the PMU perf: arm_pmuv3: Keep out of guest counter partition KVM: arm64: Make guests see only counters they can access
arch/arm/include/asm/arm_pmuv3.h | 13 ++ arch/arm64/include/asm/arm_pmuv3.h | 10 ++ arch/arm64/kvm/debug.c | 3 +- arch/arm64/kvm/pmu-emul.c | 8 +- drivers/perf/arm_pmuv3.c | 117 ++++++++++++++++-- include/linux/perf/arm_pmu.h | 2 + include/linux/perf/arm_pmuv3.h | 34 ++++- .../selftests/kvm/arm64/vpmu_counter_access.c | 2 +- 8 files changed, 168 insertions(+), 21 deletions(-)
base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b -- 2.48.1.502.g6dc24dfdaf-goog