6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
commit f9dc8fb3afc968042bdaf4b6e445a9272071c9f3 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: 94cdeebd8211 ("KVM: x86/cpuid: Add AMD CPUID ExtPerfMonAndDbg leaf 0x80000022")
Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Link: https://lore.kernel.org/r/20250304082314.472202-3-xiaoyao.li@xxxxxxxxx
[sean: massage shortlog and changelog, tag for stable]
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/cpuid.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1387,7 +1387,7 @@ static inline int __do_cpuid_func(struct
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;
}
