6.6-stable review patch. If anyone has any objections, please let me know.
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From: Xiaoyao Li xiaoyao.li@intel.com
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@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 --- 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 @@ -1307,7 +1307,7 @@ 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; }