kvm: vmx: Introduce lapic_mode enumeration

The local APIC can be in one of three modes: disabled, xAPIC or
x2APIC. (A fourth mode, "invalid," is included for completeness.)

Using the new enumeration can make some of the APIC mode logic easier
to read. In kvm_set_apic_base, for instance, it is clear that one
cannot transition directly from x2APIC mode to xAPIC mode or directly
from APIC disabled to x2APIC mode.
Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
[Check invalid bits even if msr_info->host_initiated.  Reported by
 Wanpeng Li. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.h

@@ -16,6 +16,13 @@
 #define APIC_BUS_CYCLE_NS       1
 #define APIC_BUS_FREQUENCY      (1000000000ULL / APIC_BUS_CYCLE_NS)
 
+enum lapic_mode {
+	LAPIC_MODE_DISABLED = 0,
+	LAPIC_MODE_INVALID = X2APIC_ENABLE,
+	LAPIC_MODE_XAPIC = MSR_IA32_APICBASE_ENABLE,
+	LAPIC_MODE_X2APIC = MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE,
+};
+
 struct kvm_timer {
 	struct hrtimer timer;
 	s64 period; 				/* unit: ns */
@@ -89,6 +96,7 @@ u64 kvm_get_apic_base(struct kvm_vcpu *vcpu);
 int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info);
 int kvm_apic_get_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s);
 int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s);
+enum lapic_mode kvm_get_apic_mode(struct kvm_vcpu *vcpu);
 int kvm_lapic_find_highest_irr(struct kvm_vcpu *vcpu);
 
 u64 kvm_get_lapic_tscdeadline_msr(struct kvm_vcpu *vcpu);
@@ -220,4 +228,10 @@ void kvm_lapic_switch_to_hv_timer(struct kvm_vcpu *vcpu);
 void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu);
 bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu);
 void kvm_lapic_restart_hv_timer(struct kvm_vcpu *vcpu);
+
+static inline enum lapic_mode kvm_apic_mode(u64 apic_base)
+{
+	return apic_base & (MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE);
+}
+
 #endif

arch/x86/kvm/x86.c

@@ -318,23 +318,27 @@ u64 kvm_get_apic_base(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_get_apic_base);
 
+enum lapic_mode kvm_get_apic_mode(struct kvm_vcpu *vcpu)
+{
+	return kvm_apic_mode(kvm_get_apic_base(vcpu));
+}
+EXPORT_SYMBOL_GPL(kvm_get_apic_mode);
+
 int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
-	u64 old_state = vcpu->arch.apic_base &
-		(MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE);
-	u64 new_state = msr_info->data &
-		(MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE);
+	enum lapic_mode old_mode = kvm_get_apic_mode(vcpu);
+	enum lapic_mode new_mode = kvm_apic_mode(msr_info->data);
 	u64 reserved_bits = ((~0ULL) << cpuid_maxphyaddr(vcpu)) | 0x2ff |
 		(guest_cpuid_has(vcpu, X86_FEATURE_X2APIC) ? 0 : X2APIC_ENABLE);
 
-	if ((msr_info->data & reserved_bits) || new_state == X2APIC_ENABLE)
-		return 1;
-	if (!msr_info->host_initiated &&
-	    ((new_state == MSR_IA32_APICBASE_ENABLE &&
-	      old_state == (MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE)) ||
-	     (new_state == (MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE) &&
-	      old_state == 0)))
+	if ((msr_info->data & reserved_bits) != 0 || new_mode == LAPIC_MODE_INVALID)
 		return 1;
+	if (!msr_info->host_initiated) {
+		if (old_mode == LAPIC_MODE_X2APIC && new_mode == LAPIC_MODE_XAPIC)
+			return 1;
+		if (old_mode == LAPIC_MODE_DISABLED && new_mode == LAPIC_MODE_X2APIC)
+			return 1;
+	}
 
 	kvm_lapic_set_base(vcpu, msr_info->data);
 	return 0;