Commit f9dc8fb3 authored by Xiaoyao Li's avatar Xiaoyao Li Committed by Sean Christopherson
Browse files

KVM: x86: Explicitly zero EAX and EBX when PERFMON_V2 isn't supported by KVM 



Fix a goof where KVM sets CPUID.0x80000022.EAX to CPUID.0x80000022.EBX
instead of zeroing both when PERFMON_V2 isn't supported by KVM.  In
practice, barring a buggy CPU (or vCPU model when running nested) only the
!enable_pmu case is affected, as KVM always supports PERFMON_V2 if it's
available in hardware, i.e. CPUID.0x80000022.EBX will be '0' if PERFMON_V2
is unsupported.

For the !enable_pmu case, the bug is relatively benign as KVM will refuse
to enable PMU capabilities, but a VMM that reflects KVM's supported CPUID
into the guest could inadvertently induce #GPs in the guest due to
advertising support for MSRs that KVM refuses to emulate.

Fixes: 94cdeebd ("KVM: x86/cpuid: Add AMD CPUID ExtPerfMonAndDbg leaf 0x80000022")
Signed-off-by: default avatarXiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20250304082314.472202-3-xiaoyao.li@intel.com


[sean: massage shortlog and changelog, tag for stable]
Cc: stable@vger.kernel.org
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 3b2d3db3

arch/x86/kvm/cpuid.c

+1 −1
Original line number Diff line number Diff line
@@ -1763,7 +1763,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) 


		entry->ecx = entry->edx = 0;

		if (!enable_pmu || !kvm_cpu_cap_has(X86_FEATURE_PERFMON_V2)) {

			entry->eax = entry->ebx;

			entry->eax = entry->ebx = 0;

			break;

		}