[PATCH v2 0/8] KVM: arm64: PMU: Allow userspace to limit the number of PMCs on vCPU

[Shaoqin Huang]

Hi Reiji,


I have tested this patch set on an Ampere machine, and every thing works 
fine.


Tested-by: Shaoqin Huang <shahuang at redhat.com>

On 1/17/23 09:35, Reiji Watanabe wrote:
> The goal of this series is to allow userspace to limit the number
> of PMU event counters on the vCPU. We need this to support migration
> across systems that implement different numbers of counters.
>
> The number of PMU event counters is indicated in PMCR_EL0.N.
> For a vCPU with PMUv3 configured, its value will be the same as
> the host value by default. Userspace can set PMCR_EL0.N for the
> vCPU to a lower value than the host value, using KVM_SET_ONE_REG.
> However, it is practically unsupported, as KVM resets PMCR_EL0.N
> to the host value on vCPU reset and some KVM code uses the host
> value to identify (un)implemented event counters on the vCPU.
>
> This series will ensure that the PMCR_EL0.N value is preserved
> on vCPU reset and that KVM doesn't use the host value
> to identify (un)implemented event counters on the vCPU.
> This allows userspace to limit the number of the PMU event
> counters on the vCPU.
>
> Patch 1 fixes reset_pmu_reg() to ensure that (RAZ) bits of
> {PMCNTEN,PMOVS}{SET,CLR}_EL1 corresponding to unimplemented event
> counters on the vCPU are reset to zero even when PMCR_EL0.N for
> the vCPU is different from the host.
>
> Patch 2 is a minor refactoring to use the default PMU register reset
> function (reset_pmu_reg()) for PMUSERENR_EL0 and PMCCFILTR_EL0.
> (With the Patch 1 change, reset_pmu_reg() can now be used for
> those registers)
>
> Patch 3 fixes reset_pmcr() to preserve PMCR_EL0.N for the vCPU on
> vCPU reset.
>
> Patch 4 adds the sys_reg's set_user() handler for the PMCR_EL0
> to disallow userspace to set PMCR_EL0.N for the vCPU to a value
> that is greater than the host value.
>
> Patch 5-8 adds a selftest to verify reading and writing PMU registers
> for implemented or unimplemented PMU event counters on the vCPU.
>
> The series is based on v6.2-rc4.
>
> v2:
>   - Added the sys_reg's set_user() handler for the PMCR_EL0 to
>     disallow userspace to set PMCR_EL0.N for the vCPU to a value
>     that is greater than the host value (and added a new test
>     case for this behavior). [Oliver]
>   - Added to the commit log of the patch 2 that PMUSERENR_EL0 and
>     PMCCFILTR_EL0 have UNKNOWN reset values.
>
> v1: https://lore.kernel.org/all/20221230035928.3423990-1-reijiw@google.com/
>
> Reiji Watanabe (8):
>    KVM: arm64: PMU: Have reset_pmu_reg() to clear a register
>    KVM: arm64: PMU: Use reset_pmu_reg() for PMUSERENR_EL0 and
>      PMCCFILTR_EL0
>    KVM: arm64: PMU: Preserve vCPU's PMCR_EL0.N value on vCPU reset
>    KVM: arm64: PMU: Disallow userspace to set PMCR.N greater than the
>      host value
>    tools: arm64: Import perf_event.h
>    KVM: selftests: aarch64: Introduce vpmu_counter_access test
>    KVM: selftests: aarch64: vPMU register test for implemented counters
>    KVM: selftests: aarch64: vPMU register test for unimplemented counters
>
>   arch/arm64/kvm/pmu-emul.c                     |   6 +
>   arch/arm64/kvm/sys_regs.c                     |  57 +-
>   tools/arch/arm64/include/asm/perf_event.h     | 258 +++++++
>   tools/testing/selftests/kvm/Makefile          |   1 +
>   .../kvm/aarch64/vpmu_counter_access.c         | 644 ++++++++++++++++++
>   .../selftests/kvm/include/aarch64/processor.h |   1 +
>   6 files changed, 954 insertions(+), 13 deletions(-)
>   create mode 100644 tools/arch/arm64/include/asm/perf_event.h
>   create mode 100644 tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c
>
>
> base-commit: 5dc4c995db9eb45f6373a956eb1f69460e69e6d4

-- 
Regards,
Shaoqin