KVM: LAPIC: ARBPRI is a reserved register for x2APIC

kvm-unit-tests were adjusted to match bare metal behavior, but KVM
itself was not doing what bare metal does; fix that.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -1318,7 +1318,7 @@ int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
 	unsigned char alignment = offset & 0xf;
 	u32 result;
 	/* this bitmask has a bit cleared for each reserved register */
-	static const u64 rmask = 0x43ff01ffffffe70cULL;
+	u64 rmask = 0x43ff01ffffffe70cULL;
 
 	if ((alignment + len) > 4) {
 		apic_debug("KVM_APIC_READ: alignment error %x %d\n",
@@ -1326,6 +1326,10 @@ int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
 		return 1;
 	}
 
+	/* ARBPRI is also reserved on x2APIC */
+	if (apic_x2apic_mode(apic))
+		rmask &= ~(1 << (APIC_ARBPRI >> 4));
+
 	if (offset > 0x3f0 || !(rmask & (1ULL << (offset >> 4)))) {
 		apic_debug("KVM_APIC_READ: read reserved register %x\n",
 			   offset);