Summary of changes:

- Turn ALIGN_VA() macro into inline function align_va().
- Use proper macros, round{up,down}2(9).
- Make sure that alignment is power of 2 in uvm_map_space_avail().

Index: sys/uvm/uvm_map.c
===================================================================
RCS file: /home/netbsd/src/sys/uvm/uvm_map.c,v
retrieving revision 1.364
diff -p -u -r1.364 uvm_map.c
--- sys/uvm/uvm_map.c	10 Aug 2019 01:06:45 -0000	1.364
+++ sys/uvm/uvm_map.c	2 Oct 2019 08:27:10 -0000
@@ -187,6 +187,21 @@ int user_va0_disable = __USER_VA0_DISABL
  */
 
 /*
+ * align_va: round down or up virtual address
+ */
+static __inline void
+align_va(vaddr_t *vap, vsize_t align, int topdown)
+{
+
+	if (align != 0 && (*vap & (align - 1)) != 0) {
+		if (topdown)
+			*vap = rounddown2(*vap, align);
+		else
+			*vap = roundup2(*vap, align);
+	}
+}
+
+/*
  * UVM_ET_ISCOMPATIBLE: check some requirements for map entry merging
  */
 extern struct vm_map *pager_map;
@@ -1805,13 +1820,9 @@ uvm_map_space_avail(vaddr_t *start, vsiz
 				*start = ptoa(hint + align); /* adjust to color */
 			}
 		}
-	} else if (align != 0) {
-		if ((*start & (align - 1)) != 0) {
-			if (topdown)
-				*start &= ~(align - 1);
-			else
-				*start = roundup(*start, align);
-		}
+	} else {
+		KASSERT(powerof2(align));
+		align_va(start, align, topdown);
 		/*
 		 * XXX Should we PMAP_PREFER() here again?
 		 * eh...i think we're okay
@@ -1861,7 +1872,7 @@ uvm_map_findspace(struct vm_map *map, va
 
 	UVMHIST_LOG(maphist, "(map=%#jx, hint=%#jx, len=%ju, flags=%#jx)",
 	    (uintptr_t)map, hint, length, flags);
-	KASSERT((flags & UVM_FLAG_COLORMATCH) != 0 || (align & (align - 1)) == 0);
+	KASSERT((flags & UVM_FLAG_COLORMATCH) != 0 || powerof2(align));
 	KASSERT((flags & UVM_FLAG_COLORMATCH) == 0 || align < uvmexp.ncolors);
 	KASSERT((flags & UVM_FLAG_FIXED) == 0 || align == 0);
 
@@ -1888,6 +1899,12 @@ uvm_map_findspace(struct vm_map *map, va
 	}
 
 	/*
+	 * hint may not be aligned properly; we need round up or down it
+	 * before proceeding further.
+	 */
+	align_va(&hint, align, topdown);
+
+	/*
 	 * Look for the first possible address; if there's already
 	 * something at this address, we have to start after it.
 	 */