Re: [PATCH v9 00/16] KVM: arm64: PMU: Use multiple host PMUs

[Fuad Tabba]

On Mon, 20 Jul 2026 at 06:39, Akihiko Odaki
<odaki@xxxxxxxxxxxxxxxxxxxxxx> wrote:
...
> A QEMU patch that demonstrates the usage of the new attribute is
> available at:
> https://lore.kernel.org/qemu-devel/20260706-kvm-v4-1-089cac8c25c3@xxxxxxxxxxxxxxxxxxxxxx/
> ("[PATCH RFC v4] target/arm/kvm: Choose PMU backend")
>
> Signed-off-by: Akihiko Odaki <odaki@xxxxxxxxxxxxxxxxxxxxxx>

I didn't test with the QEMU patch, but I tested on QEMU: booting the
host and a KVM guest, plus the vpmu_counter_access and get-reg-list
KVM selftests under nvhe, vhe, andvhe with kvm-arm.mode=nested.

For the series:
Tested-by: Fuad Tabba < fuad.tabba@xxxxxxxxx>

Cheers,
/fuad

> ---
> Changes in v9:
> - Dropped patch
>   "KVM: arm64: Disallow vPMU when pPMUs do not cover all CPUs".
> - Added patch
>   "KVM: arm64: PMU: Stop updating MDCR_EL2.HPMN".
> - Added patch
>   "KVM: arm64: selftests: Cover PMU state in MDCR_EL2".
> - Added patch
>   "arm64: errata: Require Apple IMPDEF PMUv3 traps on all CPUs".
> - Added patch
>   "KVM: arm64: Don't clear vcpu->cpu in kvm_arch_vcpu_put()".
> - Noted that fixed-counters-only mode avoids relying on the default PMU.
> - Clarified why fixed-counters-only mode hides PMCEID.
> - Added patch "KVM: arm64: Serialize repeated vCPU initialization".
> - Added patch "KVM: arm64: PMU: Freeze counter count after first run".
> - Added patch
>   "KVM: arm64: selftests: Test SET_NR_COUNTERS after first run".
> - Added patch "KVM: arm64: PMU: Recreate events after MDCR_EL2 changes".
> - Clarified why extra IMPDEF PMUv3 trap support on a late CPU is safe.
> - Changed fixed-counters-only emulation to taint the kernel when it
>   encounters a CPU without a registered pPMU; see the commit message.
> - Added patch
>   "KVM: arm64: PMU: Keep implemented counter mask EL-independent".
> - Added a targeted bitfield helper type change to tools headers.
> - Link to v8: https://patch.msgid.link/20260710-hybrid-v8-0-621409f3a592@xxxxxxxxxxxxxxxxxxxxxx
>
> Changes in v8:
> - Added patch
>   "KVM: arm64: Disallow vPMU when pPMUs do not cover all CPUs".
> - Split patch "KVM: arm64: PMU: Introduce FIXED_COUNTERS_ONLY".
> - Documented the FEAT_PMUv3_ICNTR support plan.
> - Ensured KVM_ARM_VCPU_PMU_V3_FILTER and
>   KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY are mutually exclusive.
> - Ensured KVM_ARM_VCPU_PMU_V3_SET_PMU and
>   KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY are mutually exclusive.
> - Dropped the code to support KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS for
>   KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY.
> - Added a function to de-duplicate
>   "test_bit(KVM_ARCH_FLAG_PMU_V3_FIXED_COUNTERS_ONLY, ...)".
> - Link to v7: https://lore.kernel.org/r/20260418-hybrid-v7-0-2bf39ad009bf@xxxxxxxxxxxxxxxxxxxxxx
>
> Changes in v7:
> - Fixed the vCPU run hang in test_fixed_counters_only().
> - Link to v6: https://lore.kernel.org/r/20260413-hybrid-v6-0-e79d760f7f1b@xxxxxxxxxxxxxxxxxxxxxx
>
> Changes in v6:
> - Removed WARN_ON_ONCE() in kvm_pmu_create_perf_event(). It can be
>   triggered in kvm_arch_vcpu_load() before it checks supported_cpus.
> - Removed an extra lockdep assertion in kvm_arm_pmu_v3_get_attr().
> - Fixed error messages in test_fixed_counters_only().
> - Fixed the vCPU run in test_fixed_counters_only().
> - Link to v5: https://lore.kernel.org/r/20260411-hybrid-v5-0-b043b4d9f49e@xxxxxxxxxxxxxxxxxxxxxx
>
> Changes in v5:
> - Rebased.
> - Fixed the order to clear KVM_ARCH_FLAG_PMU_V3_FIXED_COUNTERS_ONLY in
>   kvm_arm_pmu_v3_set_pmu().
> - Fixed the setting of KVM_ARM_VCPU_PMU_V3_IRQ in
>   test_fixed_counters_only().
> - Changed to WARN_ON_ONCE() when kvm_pmu_probe_armpmu() returns NULL in
>   kvm_pmu_create_perf_event(), which is no longer supposed to happen.
> - Link to v4: https://lore.kernel.org/r/20260317-hybrid-v4-0-bd62bcd48644@xxxxxxxxxxxxxxxxxxxxxx
>
> Changes in v4:
> - Extracted kvm_pmu_enabled_counter_mask() into a separate patch.
> - Added patch "KVM: arm64: PMU: Protect the list of PMUs with RCU".
> - Merged KVM_REQ_CREATE_PMU into KVM_REQ_RELOAD_PMU.
> - Added a check to avoid unnecessary KVM_REQ_RELOAD_PMU requests.
> - Dropped the change to avoid setting kvm_arm_set_default_pmu() when
>   KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY is not set.
> - Link to v3: https://lore.kernel.org/r/20260225-hybrid-v3-0-46e8fe220880@xxxxxxxxxxxxxxxxxxxxxx
>
> Changes in v3:
> - Renamed the attribute to KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY.
> - Changed to request the creation of perf counters when loading vCPU.
> - Link to v2: https://lore.kernel.org/r/20250806-hybrid-v2-0-0661aec3af8c@xxxxxxxxxxxxxxxxxxxxxx
>
> Changes in v2:
> - Added the KVM_ARM_VCPU_PMU_V3_COMPOSITION attribute to opt in the
>   feature.
> - Added code to handle overflow.
> - Link to v1: https://lore.kernel.org/r/20250319-hybrid-v1-1-4d1ada10e705@xxxxxxxxxx
>
> ---
> Akihiko Odaki (15):
>       KVM: arm64: Serialize repeated vCPU initialization
>       KVM: arm64: PMU: Stop updating MDCR_EL2.HPMN
>       KVM: arm64: PMU: Freeze counter count after first run
>       KVM: arm64: selftests: Test SET_NR_COUNTERS after first run
>       KVM: arm64: PMU: Keep implemented counter mask EL-independent
>       KVM: arm64: PMU: Recreate events after MDCR_EL2 changes
>       tools headers: Use u* types for bitfield helpers
>       KVM: arm64: selftests: Cover PMU state in MDCR_EL2
>       arm64: errata: Require Apple IMPDEF PMUv3 traps on all CPUs
>       KVM: arm64: PMU: Protect the list of PMUs with RCU
>       KVM: arm64: PMU: Pass the pPMU to kvm_map_pmu_event()
>       KVM: arm64: PMU: Pass the target CPU to kvm_pmu_probe_armpmu()
>       KVM: arm64: PMU: Implement fixed-counters-only emulation
>       KVM: arm64: PMU: Introduce FIXED_COUNTERS_ONLY
>       KVM: arm64: selftests: Test PMU_V3_FIXED_COUNTERS_ONLY
>
> Oliver Upton (1):
>       KVM: arm64: Don't clear vcpu->cpu in kvm_arch_vcpu_put()
>
>  Documentation/virt/kvm/devices/vcpu.rst            |  30 ++-
>  arch/arm64/include/asm/kvm_host.h                  |   4 +
>  arch/arm64/include/uapi/asm/kvm.h                  |   1 +
>  arch/arm64/kernel/cpu_errata.c                     |   2 +-
>  arch/arm64/kvm/arm.c                               |  18 +-
>  arch/arm64/kvm/pmu-emul.c                          | 241 +++++++++++------
>  arch/arm64/kvm/reset.c                             |  16 +-
>  arch/arm64/kvm/sys_regs.c                          |  31 ++-
>  include/kvm/arm_pmu.h                              |   5 +
>  tools/arch/arm64/include/uapi/asm/kvm.h            |   1 +
>  tools/include/linux/bitfield.h                     |  26 +-
>  .../selftests/kvm/arm64/vpmu_counter_access.c      | 284 ++++++++++++++++++---
>  12 files changed, 510 insertions(+), 149 deletions(-)
> ---
> base-commit: cb9360ae6549120975f20887840fb33d47c13898
> change-id: 20250224-hybrid-01d5ff47edd2
>
> Best regards,
> --
> Akihiko Odaki <odaki@xxxxxxxxxxxxxxxxxxxxxx>
>
>