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

commit f9dc8fb3af upstream.

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: 94cdeebd82 ("KVM: x86/cpuid: Add AMD CPUID ExtPerfMonAndDbg leaf 0x80000022")
Signed-off-by: Xiaoyao 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: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This commit is contained in:

Xiaoyao Li

2025-03-04 03:23:14 -05:00

committed by

Greg Kroah-Hartman

parent 9eb6f272a6

commit b33b35b8bb

1 changed files with 1 additions and 1 deletions

									
										arch/x86/kvm/cpuid.c
									
		+1
		-1
	
												View File
												
				@@ -1387,7 +1387,7 @@ 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;

						}