Re: [PATCH 2/3] target/i386: Call KVM_CAP_PMU_CAPABILITY iotcl to enable/disable PMU

[Dongli Zhang <dongli.zhang@oracle.com>]

Hi Dapeng,

PATCH 1-4 from the below patchset are already reviewed. (PATCH 5-10 are for PMU
registers reset).

https://lore.kernel.org/all/20250302220112.17653-1-dongli.zhang@oracle.com/

They require only trivial modification. i.e.:

https://github.com/finallyjustice/patchset/tree/master/qemu-amd-pmu-mid/v03

Therefore, since PATCH 5-10 are for another topic, any chance if I re-send 1-4
as a prerequisite for the patch to explicitly call KVM_CAP_PMU_CAPABILITY?

In addition, I have a silly question. Can mediated vPMU coexist with legacy
perf-based vPMU, that is, something like tdp and tdp_mmu? Or the legacy
perf-based vPMU is going to be purged from the most recent kernel?

If they can coexist, how about add property to QEMU control between
legacy/modern? i.e. by default use legacy and change to modern as default in the
future once the feature is stable.

Thank you very much!

Dongli Zhang

On 3/24/25 5:37 AM, Dapeng Mi wrote:
> After introducing mediated vPMU, mediated vPMU must be enabled by
> explicitly calling KVM_CAP_PMU_CAPABILITY to enable. Thus call
> KVM_CAP_PMU_CAPABILITY to enable/disable PMU base on user configuration.
> 
> Suggested-by: Zhao Liu <zhao1.liu@intel.com>
> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> ---
>  target/i386/kvm/kvm.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index f41e190fb8..d3e6984844 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -2051,8 +2051,25 @@ full:
>      abort();
>  }
>  
> +static bool pmu_cap_set = false;
>  int kvm_arch_pre_create_vcpu(CPUState *cpu, Error **errp)
>  {
> +    KVMState *s = kvm_state;
> +    X86CPU *x86_cpu = X86_CPU(cpu);
> +
> +    if (!pmu_cap_set && kvm_check_extension(s, KVM_CAP_PMU_CAPABILITY)) {
> +        int r = kvm_vm_enable_cap(s, KVM_CAP_PMU_CAPABILITY, 0,
> +                                  KVM_PMU_CAP_DISABLE & !x86_cpu->enable_pmu);
> +        if (r < 0) {
> +            error_report("kvm: Failed to %s pmu cap: %s",
> +                         x86_cpu->enable_pmu ? "enable" : "disable",
> +                         strerror(-r));
> +            return r;
> +        }
> +
> +        pmu_cap_set = true;
> +    }
> +
>      return 0;
>  }
>