KVM: x86/pmu: Don't try to get perf capabilities for hybrid CPUs

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: 51f34b1 ("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]
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: Dapeng Mi

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) {
 		/*