Index: sys/amd64/amd64/pmap.c
===================================================================
--- sys/amd64/amd64/pmap.c
+++ sys/amd64/amd64/pmap.c
@@ -957,6 +957,13 @@
 		pd_p[i] = (i << PDRSHIFT) | X86_PG_RW | X86_PG_V | PG_PS |
 		    pg_g;
 
+	/*
+	 * Because we map the physical blocks in 2M pages, adjust firstaddr
+	 * to record the physical blocks we've actually mapped into kernel
+	 * virtual address space.
+	 */
+	*firstaddr = round_2mpage(*firstaddr);
+
 	/* And connect up the PD to the PDP (leaving room for L4 pages) */
 	pdp_p = (pdp_entry_t *)(KPDPphys + ptoa(KPML4I - KPML4BASE));
 	for (i = 0; i < nkpdpe; i++)