@@ -778,6 +778,39 @@ exception.
 * -KVM_EBUSY - another *KVMI_VCPU_INJECT_EXCEPTION*-*KVMI_VCPU_EVENT_TRAP*
                pair is in progress
 
+17. KVMI_VCPU_GET_XCR
+---------------------
+
+:Architectures: x86
+:Versions: >= 1
+:Parameters:
+
+::
+
+	struct kvmi_vcpu_hdr;
+	struct kvmi_vcpu_get_xcr {
+		__u8 xcr;
+		__u8 padding[7];
+	};
+
+:Returns:
+
+::
+
+	struct kvmi_error_code;
+	struct kvmi_vcpu_get_xcr_reply {
+		__u64 value;
+	};
+
+Returns the value of an extended control register XCR.
+
+:Errors:
+
+* -KVM_EINVAL - the selected vCPU is invalid
+* -KVM_EINVAL - the specified control register is not XCR0
+* -KVM_EINVAL - the padding is not zero
+* -KVM_EAGAIN - the selected vCPU can't be introspected yet
+
 Events
 ======
 

@@ -102,4 +102,13 @@ struct kvmi_vcpu_event_xsetbv {
 	__u64 new_value;
 };
 
+struct kvmi_vcpu_get_xcr {
+	__u8 xcr;
+	__u8 padding[7];
+};
+
+struct kvmi_vcpu_get_xcr_reply {
+	__u64 value;
+};
+
 #endif /* _UAPI_ASM_X86_KVMI_H */

@@ -174,11 +174,32 @@ static int handle_vcpu_inject_exception(const struct kvmi_vcpu_msg_job *job,
 	return kvmi_msg_vcpu_reply(job, msg, ec, NULL, 0);
 }
 
+static int handle_vcpu_get_xcr(const struct kvmi_vcpu_msg_job *job,
+			       const struct kvmi_msg_hdr *msg,
+			       const void *_req)
+{
+	const struct kvmi_vcpu_get_xcr *req = _req;
+	struct kvmi_vcpu_get_xcr_reply rpl;
+	int ec = 0;
+
+	memset(&rpl, 0, sizeof(rpl));
+
+	if (non_zero_padding(req->padding, ARRAY_SIZE(req->padding)))
+		ec = -KVM_EINVAL;
+	else if (req->xcr != 0)
+		ec = -KVM_EINVAL;
+	else
+		rpl.value = job->vcpu->arch.xcr0;
+
+	return kvmi_msg_vcpu_reply(job, msg, ec, &rpl, sizeof(rpl));
+}
+
 static const kvmi_vcpu_msg_job_fct msg_vcpu[] = {
 	[KVMI_VCPU_CONTROL_CR]       = handle_vcpu_control_cr,
 	[KVMI_VCPU_GET_CPUID]        = handle_vcpu_get_cpuid,
 	[KVMI_VCPU_GET_INFO]         = handle_vcpu_get_info,
 	[KVMI_VCPU_GET_REGISTERS]    = handle_vcpu_get_registers,
+	[KVMI_VCPU_GET_XCR]          = handle_vcpu_get_xcr,
 	[KVMI_VCPU_INJECT_EXCEPTION] = handle_vcpu_inject_exception,
 	[KVMI_VCPU_SET_REGISTERS]    = handle_vcpu_set_registers,
 };

@@ -43,6 +43,7 @@ enum {
 	KVMI_VCPU_GET_CPUID        = KVMI_VCPU_MESSAGE_ID(5),
 	KVMI_VCPU_CONTROL_CR       = KVMI_VCPU_MESSAGE_ID(6),
 	KVMI_VCPU_INJECT_EXCEPTION = KVMI_VCPU_MESSAGE_ID(7),
+	KVMI_VCPU_GET_XCR          = KVMI_VCPU_MESSAGE_ID(8),
 
 	KVMI_NEXT_VCPU_MESSAGE
 };

@@ -1405,6 +1405,38 @@ static void test_event_xsetbv(struct kvm_vm *vm)
 	disable_vcpu_event(vm, event_id);
 }
 
+static void cmd_vcpu_get_xcr(struct kvm_vm *vm, u8 xcr, u64 *value,
+			     int expected_err)
+{
+	struct {
+		struct kvmi_msg_hdr hdr;
+		struct kvmi_vcpu_hdr vcpu_hdr;
+		struct kvmi_vcpu_get_xcr cmd;
+	} req = { 0 };
+	struct kvmi_vcpu_get_xcr_reply rpl = { 0 };
+	int r;
+
+	req.cmd.xcr = xcr;
+
+	r = do_vcpu0_command(vm, KVMI_VCPU_GET_XCR, &req.hdr, sizeof(req),
+			     &rpl, sizeof(rpl));
+	TEST_ASSERT(r == expected_err,
+		"KVMI_VCPU_GET_XCR failed, error %d (%s), expected %d\n",
+		-r, kvm_strerror(-r), expected_err);
+
+	*value = r == 0 ? rpl.value : 0;
+}
+
+static void test_cmd_vcpu_get_xcr(struct kvm_vm *vm)
+{
+	u8 xcr0 = 0, xcr1 = 1;
+	u64 value;
+
+	cmd_vcpu_get_xcr(vm, xcr0, &value, 0);
+	pr_debug("XCR0 0x%lx\n", value);
+	cmd_vcpu_get_xcr(vm, xcr1, &value, -KVM_EINVAL);
+}
+
 static void test_introspection(struct kvm_vm *vm)
 {
 	srandom(time(0));

@@ -1431,6 +1463,7 @@ static void test_introspection(struct kvm_vm *vm)
 	test_cmd_vcpu_control_cr(vm);
 	test_cmd_vcpu_inject_exception(vm);
 	test_event_xsetbv(vm);
+	test_cmd_vcpu_get_xcr(vm);
 
 	unhook_introspection(vm);
 }