KVM: SVM: Emulate read/write access to cr8

This patch adds code to emulate the access to the cr8 register to the x86
instruction emulator in kvm.  This is needed on svm, where there is no
hardware decode for control register access.
Signed-off-by: NJoerg Roedel <joerg.roedel@amd.com>
Signed-off-by: NMarkus Rechberger <markus.rechberger@amd.com>
Signed-off-by: NAvi Kivity <avi@qumranet.com>

drivers/kvm/x86.c

@@ -2236,6 +2236,8 @@ unsigned long realmode_get_cr(struct kvm_vcpu *vcpu, int cr)
 		return vcpu->cr3;
 	case 4:
 		return vcpu->cr4;
+	case 8:
+		return get_cr8(vcpu);
 	default:
 		vcpu_printf(vcpu, "%s: unexpected cr %u\n", __FUNCTION__, cr);
 		return 0;
@@ -2259,6 +2261,9 @@ void realmode_set_cr(struct kvm_vcpu *vcpu, int cr, unsigned long val,
 	case 4:
 		set_cr4(vcpu, mk_cr_64(vcpu->cr4, val));
 		break;
+	case 8:
+		set_cr8(vcpu, val & 0xfUL);
+		break;
 	default:
 		vcpu_printf(vcpu, "%s: unexpected cr %u\n", __FUNCTION__, cr);
 	}