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

["Borah, Chaitanya Kumar" <chaitanya.kumar.borah@intel.com>]

On 10/13/2025 4:07 PM, Jani Nikula wrote:
> 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.
> 

Ack, please consider it

Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>

Thank you for pointing it out.
> 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) {
>>   		/*
>