kvm: x86: CPUID.01H:EDX.APIC[bit 9] should mirror IA32_APIC_BASE[11]

From the Intel SDM, volume 3, section 10.4.3, "Enabling or Disabling the
Local APIC,"

  When IA32_APIC_BASE[11] is 0, the processor is functionally equivalent
  to an IA-32 processor without an on-chip APIC. The CPUID feature flag
  for the APIC (see Section 10.4.2, "Presence of the Local APIC") is
  also set to 0.
Signed-off-by: Jim Mattson <jmattson@google.com>
[Changed subject tag from nVMX to x86.]
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/cpuid.c

@@ -87,6 +87,10 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 			best->ecx |= F(OSXSAVE);
 	}
 
+	best->edx &= ~F(APIC);
+	if (vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE)
+		best->edx |= F(APIC);
+
 	if (apic) {
 		if (best->ecx & F(TSC_DEADLINE_TIMER))
 			apic->lapic_timer.timer_mode_mask = 3 << 17;

arch/x86/kvm/lapic.c

@@ -1806,14 +1806,17 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
 	u64 old_value = vcpu->arch.apic_base;
 	struct kvm_lapic *apic = vcpu->arch.apic;
 
-	if (!apic) {
+	if (!apic)
 		value |= MSR_IA32_APICBASE_BSP;
-		vcpu->arch.apic_base = value;
-		return;
-	}
 
 	vcpu->arch.apic_base = value;
 
+	if ((old_value ^ value) & MSR_IA32_APICBASE_ENABLE)
+		kvm_update_cpuid(vcpu);
+
+	if (!apic)
+		return;
+
 	/* update jump label if enable bit changes */
 	if ((old_value ^ value) & MSR_IA32_APICBASE_ENABLE) {
 		if (value & MSR_IA32_APICBASE_ENABLE) {