Index: kernel/bus/drv/drv.c
===================================================================
--- kernel/bus/drv/drv.c	(revision 2386)
+++ kernel/bus/drv/drv.c	(working copy)
@@ -843,6 +843,9 @@
 	// "Enable Quality of Service support in the HCA if > 0, (default 1)"
 	DECLARE_CONST_UNICODE_STRING(enableQoS, L"EnableQoS");	
 
+	// "Block multicast loopback packets if > 0 (default 1)"
+	DECLARE_CONST_UNICODE_STRING(BlockMcastLB, L"BlockMcastLoopBack");	
+
 	ULONG value;
 	WDFKEY hKey = NULL;
 	NTSTATUS status = STATUS_SUCCESS;
@@ -897,6 +900,12 @@
 		else
 			g.enable_qos = 1;
 
+		status = WdfRegistryQueryULong(hKey, &BlockMcastLB, &value);
+		if (NT_SUCCESS (status)) 
+			g.mlx4_blck_lb = value;
+		else
+			g.mlx4_blck_lb = 1;
+
 		WdfRegistryClose(hKey);
 		status = STATUS_SUCCESS;
 	}
Index: kernel/bus/drv/mlx4_bus.inf
===================================================================
--- kernel/bus/drv/mlx4_bus.inf	(revision 2386)
+++ kernel/bus/drv/mlx4_bus.inf	(working copy)
@@ -147,6 +147,7 @@
 HKR,"Parameters","LogNumMpt",%REG_DWORD%,0x00000011
 HKR,"Parameters","LogNumMtt",%REG_DWORD%,0x00000014
 HKR,"Parameters","EnableQoS",%REG_DWORD%,0x00000001
+HKR,"Parameters","BlockMcastLoopBack",%REG_DWORD%,0x00000001
 
 HKLM,"System\CurrentControlSet\Control\WMI\GlobalLogger\E51BB6E2-914A-4e21-93C0-192F4801BBFF","Flags",%REG_DWORD%,0xffff
 HKLM,"System\CurrentControlSet\Control\WMI\GlobalLogger\E51BB6E2-914A-4e21-93C0-192F4801BBFF","Level",%REG_DWORD%,0x3
Index: kernel/bus/net/mcg.c
===================================================================
--- kernel/bus/net/mcg.c	(revision 2386)
+++ kernel/bus/net/mcg.c	(working copy)
@@ -204,13 +204,15 @@
 	}
 
 	for (i = 0; i < members_count; ++i)
-		if (mgm->qp[i] == cpu_to_be32(qp->qpn)) {
+		if ((be32_to_cpu(mgm->qp[i]) & MGM_QPN_MASK) == qp->qpn) {
 			mlx4_dbg(dev, "QP %06x already a member of MGM\n", qp->qpn);
 			err = 0;
 			goto out;
 		}
 
-	mgm->qp[members_count++] = cpu_to_be32(qp->qpn);
+	mgm->qp[members_count++] = cpu_to_be32((qp->qpn & MGM_QPN_MASK) |
+					       (!!g.mlx4_blck_lb << MGM_BLCK_LB_BIT));
+
 	mgm->members_count       = cpu_to_be32(members_count);
 
 	err = mlx4_WRITE_MCG(dev, index, mailbox);
@@ -285,7 +287,7 @@
 
 	members_count = be32_to_cpu(mgm->members_count);
 	for (loc = -1, i = 0; i < (int)members_count; ++i)
-		if (mgm->qp[i] == cpu_to_be32(qp->qpn))
+		if ((be32_to_cpu(mgm->qp[i]) & MGM_QPN_MASK) == qp->qpn)
 			loc = i;
 
 	if (loc == -1) {
Index: kernel/bus/net/mlx4.h
===================================================================
--- kernel/bus/net/mlx4.h	(revision 2386)
+++ kernel/bus/net/mlx4.h	(working copy)
@@ -73,6 +73,7 @@
 	int mod_num_mtt;
 
 	int enable_qos;
+	int mlx4_blck_lb;
 } GLOBALS;
 #pragma warning(default:4201) // nameless struct/union
 
@@ -114,6 +115,9 @@
 	MLX4_NUM_CMPTS		= MLX4_CMPT_NUM_TYPE << MLX4_CMPT_SHIFT
 };
 
+#define MGM_QPN_MASK       0x00FFFFFF
+#define MGM_BLCK_LB_BIT    30
+
 struct mlx4_bitmap {
 	u32			last;
 	u32			top;