Re: [core-for-CI] KVM: x86/pmu: Don't try to get perf capabilities for hybrid CPUs

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 13 Oct 2025, Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com> wrote:
> From: Dapeng Mi <dapeng1.mi@linux.intel.com>
>
> Explicitly zero kvm_host_pmu instead of attempting to get the perf PMU
> capabilities when running on a hybrid CPU to avoid running afoul of perf's
> sanity check.
>
>   ------------[ cut here ]------------
>   WARNING: arch/x86/events/core.c:3089 at perf_get_x86_pmu_capability+0xd/0xc0,
>   Call Trace:
>    <TASK>
>    kvm_x86_vendor_init+0x1b0/0x1a40 [kvm]
>    vmx_init+0xdb/0x260 [kvm_intel]
>    vt_init+0x12/0x9d0 [kvm_intel]
>    do_one_initcall+0x60/0x3f0
>    do_init_module+0x97/0x2b0
>    load_module+0x2d08/0x2e30
>    init_module_from_file+0x96/0xe0
>    idempotent_init_module+0x117/0x330
>    __x64_sys_finit_module+0x73/0xe0
>
> Always read the capabilities for non-hybrid CPUs, i.e. don't entirely
> revert to reading capabilities if and only if KVM wants to use a PMU, as
> it may be useful to have the host PMU capabilities available, e.g. if only
> or debug.
>
> Reported-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
> Closes: https://lore.kernel.org/all/70b64347-2aca-4511-af78-a767d5fa8226@intel.com/
> Fixes: 51f34b1e650f ("KVM: x86/pmu: Snapshot host (i.e. perf's) reported PMU capabilities")
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> Link: https://lore.kernel.org/r/20251010005239.146953-1-dapeng1.mi@linux.intel.com
> [sean: rework changelog, call out hybrid CPUs in shortlog]
> References: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/15122
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Chaitanya, please reply with your Signed-off-by, otherwise I can't merge
this. You *must* add your Signed-off-by even when sending someone else's
work unmodified.

BR,
Jani.


> ---
>  arch/x86/kvm/pmu.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 40ac4cb44ed2..487ad19a236e 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -108,16 +108,18 @@ void kvm_init_pmu_capability(const struct kvm_pmu_ops *pmu_ops)
>  	bool is_intel = boot_cpu_data.x86_vendor == X86_VENDOR_INTEL;
>  	int min_nr_gp_ctrs = pmu_ops->MIN_NR_GP_COUNTERS;
>  
> -	perf_get_x86_pmu_capability(&kvm_host_pmu);
> -
>  	/*
>  	 * Hybrid PMUs don't play nice with virtualization without careful
>  	 * configuration by userspace, and KVM's APIs for reporting supported
>  	 * vPMU features do not account for hybrid PMUs.  Disable vPMU support
>  	 * for hybrid PMUs until KVM gains a way to let userspace opt-in.
>  	 */
> -	if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU))
> +	if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU)) {
>  		enable_pmu = false;
> +		memset(&kvm_host_pmu, 0, sizeof(kvm_host_pmu));
> +	} else {
> +		perf_get_x86_pmu_capability(&kvm_host_pmu);
> +	}
>  
>  	if (enable_pmu) {
>  		/*

-- 
Jani Nikula, Intel