Index: sys/kern/subr_physmem.c
===================================================================
--- sys/kern/subr_physmem.c
+++ sys/kern/subr_physmem.c
@@ -63,9 +63,14 @@
 #endif
 
 #if defined(__arm__)
+/*
+ * arm's MAX_PHYS_ADDR is defined to be just below KERNBASE, which isn't quite
+ * what we want.  What we really want isn't established until a little later in
+ * the boot process, so we fudge it here.
+ */
 #define	MAX_PHYS_ADDR	0xFFFFFFFFull
-#elif defined(__aarch64__) || defined(__riscv)
-#define	MAX_PHYS_ADDR	0xFFFFFFFFFFFFFFFFull
+#else
+#define	MAX_PHYS_ADDR	VM_MAX_ADDRESS
 #endif
 
 struct region {
@@ -166,8 +171,9 @@
 	availsz = 0;
 	acnt = 0;
 	for (hwi = 0, hwp = hwregions; hwi < hwcnt; ++hwi, ++hwp) {
-		start = hwp->addr;
-		end   = hwp->size + start;
+		/* Operate on page boundaries.  Partial pages aren't usable. */
+		start = round_page(hwp->addr);
+		end   = trunc_page(hwp->size + start);
 		totalmem += atop((vm_offset_t)(end - start));
 		for (exi = 0, exp = exregions; exi < excnt; ++exi, ++exp) {
 			/*
@@ -176,8 +182,9 @@
 			 */
 			if ((exp->flags & exflags) == 0)
 				continue;
-			xstart = exp->addr;
-			xend   = exp->size + xstart;
+			/* Whole page is excluded. */
+			xstart = trunc_page(exp->addr);
+			xend   = round_page(exp->size + xstart);
 			/*
 			 * If the excluded region ends before this hw region,
 			 * continue checking with the next excluded region.