Index: head/sys/dev/hyperv/vmbus/hv_hv.c
===================================================================
--- head/sys/dev/hyperv/vmbus/hv_hv.c
+++ head/sys/dev/hyperv/vmbus/hv_hv.c
@@ -50,6 +50,35 @@
 
 #define	HYPERV_INTERFACE		0x31237648	/* HV#1 */
 
+/*
+ * The guest OS needs to register the guest ID with the hypervisor.
+ * The guest ID is a 64 bit entity and the structure of this ID is
+ * specified in the Hyper-V specification:
+ *
+ * http://msdn.microsoft.com/en-us/library/windows/
+ * hardware/ff542653%28v=vs.85%29.aspx
+ *
+ * While the current guideline does not specify how FreeBSD guest ID(s)
+ * need to be generated, our plan is to publish the guidelines for
+ * FreeBSD and other guest operating systems that currently are hosted
+ * on Hyper-V. The implementation here conforms to this yet
+ * unpublished guidelines.
+ *
+ * Bit(s)
+ * 63    - Indicates if the OS is Open Source or not; 1 is Open Source
+ * 62:56 - Os Type: FreeBSD is 0x02
+ * 55:48 - Distro specific identification
+ * 47:16 - FreeBSD kernel version number
+ * 15:0  - Distro specific identification
+ */
+#define HYPERV_GUESTID_OSS		(0x1ULL << 63)
+#define HYPERV_GUESTID_FREEBSD		(0x02ULL << 56)
+#define HYPERV_GUESTID(id)				\
+	(HYPERV_GUESTID_OSS | HYPERV_GUESTID_FREEBSD |	\
+	 (((uint64_t)(((id) & 0xff0000) >> 16)) << 48) |\
+	 (((uint64_t)__FreeBSD_version) << 16) |	\
+	 ((uint64_t)((id) & 0x00ffff)))
+
 static u_int hv_get_timecount(struct timecounter *tc);
 
 u_int	hyperv_features;
@@ -143,13 +172,6 @@
 	    goto cleanup;
 
 	/*
-	 * Write our OS info
-	 */
-	uint64_t os_guest_info = HV_FREEBSD_GUEST_ID;
-	wrmsr(HV_X64_MSR_GUEST_OS_ID, os_guest_info);
-	hv_vmbus_g_context.guest_id = os_guest_info;
-
-	/*
 	 * See if the hypercall page is already set
 	 */
 	hypercall_msr.as_uint64_t = rdmsr(HV_X64_MSR_HYPERCALL);
@@ -192,16 +214,13 @@
 void
 hv_vmbus_cleanup(void) 
 {
-	hv_vmbus_x64_msr_hypercall_contents hypercall_msr;
+	if (hv_vmbus_g_context.hypercall_page != NULL) {
+		hv_vmbus_x64_msr_hypercall_contents hypercall_msr;
 
-	if (hv_vmbus_g_context.guest_id == HV_FREEBSD_GUEST_ID) {
-	    if (hv_vmbus_g_context.hypercall_page != NULL) {
 		hypercall_msr.as_uint64_t = 0;
-		wrmsr(HV_X64_MSR_HYPERCALL,
-					hypercall_msr.as_uint64_t);
+		wrmsr(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64_t);
 		free(hv_vmbus_g_context.hypercall_page, M_DEVBUF);
 		hv_vmbus_g_context.hypercall_page = NULL;
-	    }
 	}
 }
 
@@ -508,6 +527,9 @@
 		return;
 	}
 
+	/* Write guest id */
+	wrmsr(HV_X64_MSR_GUEST_OS_ID, HYPERV_GUESTID(0));
+
 	if (hyperv_features & HV_FEATURE_MSR_TIME_REFCNT) {
 		/* Register virtual timecount */
 		tc_init(&hv_timecounter);
Index: head/sys/dev/hyperv/vmbus/hv_vmbus_priv.h
===================================================================
--- head/sys/dev/hyperv/vmbus/hv_vmbus_priv.h
+++ head/sys/dev/hyperv/vmbus/hv_vmbus_priv.h
@@ -198,7 +198,6 @@
 #define HV_HYPERCALL_PARAM_ALIGN sizeof(uint64_t)
 
 typedef struct {
-	uint64_t	guest_id;
 	void*		hypercall_page;
 	hv_bool_uint8_t	syn_ic_initialized;
 
@@ -763,44 +762,6 @@
 /* Wait for device creation */
 void			vmbus_scan(void);
 
-/*
- * The guest OS needs to register the guest ID with the hypervisor.
- * The guest ID is a 64 bit entity and the structure of this ID is
- * specified in the Hyper-V specification:
- *
- * http://msdn.microsoft.com/en-us/library/windows/
- * hardware/ff542653%28v=vs.85%29.aspx
- *
- * While the current guideline does not specify how FreeBSD guest ID(s)
- * need to be generated, our plan is to publish the guidelines for
- * FreeBSD and other guest operating systems that currently are hosted
- * on Hyper-V. The implementation here conforms to this yet
- * unpublished guidelines.
- *
- * Bit(s)
- * 63 - Indicates if the OS is Open Source or not; 1 is Open Source
- * 62:56 - Os Type; Linux is 0x100, FreeBSD is 0x200
- * 55:48 - Distro specific identification
- * 47:16 - FreeBSD kernel version number
- * 15:0  - Distro specific identification
- *
- */
-
-#define HV_FREEBSD_VENDOR_ID	0x8200
-#define HV_FREEBSD_GUEST_ID	hv_generate_guest_id(0,0)
-
-static inline  uint64_t hv_generate_guest_id(
-	uint8_t distro_id_part1,
-	uint16_t distro_id_part2)
-{
-	uint64_t guest_id;
-	guest_id =  (((uint64_t)HV_FREEBSD_VENDOR_ID) << 48);
-	guest_id |= (((uint64_t)(distro_id_part1)) << 48);
-	guest_id |= (((uint64_t)(__FreeBSD_version)) << 16); /* in param.h */
-	guest_id |= ((uint64_t)(distro_id_part2));
-	return guest_id;
-}
-
 typedef struct {
 	unsigned int	vector;
 	void		*page_buffers[2 * MAXCPU];