Index: sys/amd64/include/vmparam.h
===================================================================
--- sys/amd64/include/vmparam.h
+++ sys/amd64/include/vmparam.h
@@ -176,7 +176,7 @@
 #define	VM_MIN_ADDRESS		(0)
 
 #define	PHYS_TO_DMAP(x)	({						\
-	KASSERT((x) < dmaplimit,					\
+	KASSERT(dmaplimit == 0 || (x) < dmaplimit,			\
 	    ("physical address %#jx not covered by the DMAP",		\
 	    (uintmax_t)x));						\
 	(x) | DMAP_MIN_ADDRESS; })