Index: sys/dev/hyperv/hvsock/hv_sock.c
===================================================================
--- sys/dev/hyperv/hvsock/hv_sock.c
+++ sys/dev/hyperv/hvsock/hv_sock.c
@@ -74,6 +74,8 @@
 
 MALLOC_DEFINE(M_HVSOCK, "hyperv_socket", "hyperv socket control structures");
 
+static int hvs_dom_probe(void);
+
 /* The MTU is 16KB per host side's design */
 #define HVSOCK_MTU_SIZE		(1024 * 16)
 #define HVSOCK_SEND_BUF_SZ	(PAGE_SIZE - sizeof(struct vmpipe_proto_header))
@@ -124,6 +126,7 @@
 static struct domain		hv_socket_domain = {
 	.dom_family =		AF_HYPERV,
 	.dom_name =		"hyperv",
+	.dom_probe =		hvs_dom_probe,
 	.dom_protosw =		hv_socket_protosw,
 	.dom_protoswNPROTOSW =	&hv_socket_protosw[nitems(hv_socket_protosw)]
 };
@@ -322,6 +325,16 @@
 	sx_xunlock(&hvs_trans_socks_sx);
 }
 
+static int
+hvs_dom_probe(void)
+{
+
+	/* Don't even give us a chance to attach on non-HyperV. */
+	if (vm_guest != VM_GUEST_HV)
+		return (ENXIO);
+	return (0);
+}
+
 void
 hvs_trans_init(void)
 {
@@ -329,9 +342,6 @@
 	if (!IS_DEFAULT_VNET(curvnet))
 		return;
 
-	if (vm_guest != VM_GUEST_HV)
-		return;
-
 	HVSOCK_DBG(HVSOCK_DBG_VERBOSE,
 	    "%s: HyperV Socket hvs_trans_init called\n", __func__);
 
@@ -354,9 +364,6 @@
 {
 	struct hvs_pcb *pcb = so2hvspcb(so);
 
-	if (vm_guest != VM_GUEST_HV)
-		return (ESOCKTNOSUPPORT);
-
 	HVSOCK_DBG(HVSOCK_DBG_VERBOSE,
 	    "%s: HyperV Socket hvs_trans_attach called\n", __func__);
 
@@ -383,9 +390,6 @@
 {
 	struct hvs_pcb *pcb;
 
-	if (vm_guest != VM_GUEST_HV)
-		return;
-
 	HVSOCK_DBG(HVSOCK_DBG_VERBOSE,
 	    "%s: HyperV Socket hvs_trans_detach called\n", __func__);
 
@@ -595,9 +599,6 @@
 {
 	struct hvs_pcb *pcb;
 
-	if (vm_guest != VM_GUEST_HV)
-		return (ESOCKTNOSUPPORT);
-
 	HVSOCK_DBG(HVSOCK_DBG_VERBOSE,
 	    "%s: HyperV Socket hvs_trans_disconnect called\n", __func__);
 
@@ -925,9 +926,6 @@
 {
 	struct hvs_pcb *pcb;
 
-	if (vm_guest != VM_GUEST_HV)
-		return;
-
 	HVSOCK_DBG(HVSOCK_DBG_VERBOSE,
 	    "%s: HyperV Socket hvs_trans_close called\n", __func__);
 
@@ -969,9 +967,6 @@
 {
 	struct hvs_pcb *pcb = so2hvspcb(so);
 
-	if (vm_guest != VM_GUEST_HV)
-		return;
-
 	HVSOCK_DBG(HVSOCK_DBG_VERBOSE,
 	    "%s: HyperV Socket hvs_trans_abort called\n", __func__);
 
Index: sys/kern/uipc_domain.c
===================================================================
--- sys/kern/uipc_domain.c
+++ sys/kern/uipc_domain.c
@@ -170,9 +170,13 @@
 void
 domain_init(void *arg)
 {
-	struct domain *dp = arg;
+	struct domain_set_args *dsa = arg;
+	struct domain *dp;
 	struct protosw *pr;
 
+	if (!dsa->dsa_supported)
+		return;
+	dp = dsa->dsa_dp;
 	if (dp->dom_init)
 		(*dp->dom_init)();
 	for (pr = dp->dom_protosw; pr < dp->dom_protoswNPROTOSW; pr++)
@@ -198,8 +202,12 @@
 void
 vnet_domain_uninit(void *arg)
 {
-	struct domain *dp = arg;
+	struct domain_set_args *dsa = arg;
+	struct domain *dp;
 
+	if (!dsa->dsa_supported)
+		return;
+	dp = dsa->dsa_dp;
 	if (dp->dom_destroy)
 		(*dp->dom_destroy)();
 }
@@ -213,9 +221,14 @@
 void
 domain_add(void *data)
 {
+	struct domain_set_args *dsa;
 	struct domain *dp;
 
-	dp = (struct domain *)data;
+	dsa = data;
+	dp = dsa->dsa_dp;
+	if (dp->dom_probe != NULL && (*dp->dom_probe)() != 0)
+		return;
+	dsa->dsa_supported = 1;
 	mtx_lock(&dom_mtx);
 	dp->dom_next = domains;
 	domains = dp;
Index: sys/sys/domain.h
===================================================================
--- sys/sys/domain.h
+++ sys/sys/domain.h
@@ -49,6 +49,7 @@
 struct domain {
 	int	dom_family;		/* AF_xxx */
 	char	*dom_name;
+	int	(*dom_probe)(void);	/* check for support (optional) */
 	void	(*dom_init)		/* initialize domain data structures */
 		(void);
 	void	(*dom_destroy)		/* cleanup structures / state */
@@ -79,20 +80,36 @@
 void		vnet_domain_uninit(void *);
 #endif
 
+struct domain_set_args {
+	struct domain	*dsa_dp;
+	int		 dsa_supported;
+};
+
 #define	DOMAIN_SET(name)						\
+	static struct domain_set_args name ## domain_set_args = {	\
+		.dsa_dp = & name ## domain,				\
+	};								\
 	SYSINIT(domain_add_ ## name, SI_SUB_PROTO_DOMAIN,		\
-	    SI_ORDER_FIRST, domain_add, & name ## domain);		\
+	    SI_ORDER_FIRST, domain_add, &name ## domain_set_args);	\
 	SYSINIT(domain_init_ ## name, SI_SUB_PROTO_DOMAIN,		\
-	    SI_ORDER_SECOND, domain_init, & name ## domain);
+	    SI_ORDER_SECOND, domain_init, &name ## domain_set_args);
 #ifdef VIMAGE
+/*
+ * There's no such thing as per-vnet domains, so domain_set_args don't really
+ * need to be virtualized at the moment.  Further consideration would be needed
+ * for such a concept to work at all.
+ */
 #define	VNET_DOMAIN_SET(name)						\
+	static struct domain_set_args name ## domain_set_args = {	\
+		.dsa_dp = & name ## domain,				\
+	};								\
 	SYSINIT(domain_add_ ## name, SI_SUB_PROTO_DOMAIN,		\
-	    SI_ORDER_FIRST, domain_add, & name ## domain);		\
+	    SI_ORDER_FIRST, domain_add, &name ## domain_set_args);	\
 	VNET_SYSINIT(vnet_domain_init_ ## name, SI_SUB_PROTO_DOMAIN,	\
-	    SI_ORDER_SECOND, vnet_domain_init, & name ## domain);	\
+	    SI_ORDER_SECOND, vnet_domain_init, &name ## domain_set_args); \
 	VNET_SYSUNINIT(vnet_domain_uninit_ ## name,			\
 	    SI_SUB_PROTO_DOMAIN, SI_ORDER_SECOND, vnet_domain_uninit,	\
-	    & name ## domain)
+	    &name ## domain_set_args);
 #else /* !VIMAGE */
 #define	VNET_DOMAIN_SET(name)	DOMAIN_SET(name)
 #endif /* VIMAGE */