Index: sys/dev/iommu/iommu_gas.c
===================================================================
--- sys/dev/iommu/iommu_gas.c
+++ sys/dev/iommu/iommu_gas.c
@@ -142,24 +142,35 @@
 static void
 iommu_gas_augment_entry(struct iommu_map_entry *entry)
 {
-	struct iommu_map_entry *child;
+	struct iommu_map_entry *left, *right;
 	iommu_gaddr_t free_down;
+	bool changed;
 
-	free_down = 0;
-	if ((child = RB_LEFT(entry, rb_entry)) != NULL) {
-		free_down = MAX(free_down, child->free_down);
-		free_down = MAX(free_down, entry->start - child->last);
-		entry->first = child->first;
-	} else
+	left = RB_LEFT(entry, rb_entry);
+	right = RB_RIGHT(entry, rb_entry);
+	if (left == NULL && right == NULL) {
 		entry->first = entry->start;
-	
-	if ((child = RB_RIGHT(entry, rb_entry)) != NULL) {
-		free_down = MAX(free_down, child->free_down);
-		free_down = MAX(free_down, child->first - entry->end);
-		entry->last = child->last;
-	} else
 		entry->last = entry->end;
-	entry->free_down = free_down;
+		entry->free_down = 0;
+		return;
+	}
+	if (left == NULL) {
+		entry->first = entry->start;
+		entry->last = right->last;
+		entry->free_down = right->first - entry->end;
+		return;
+	}
+	if (right == NULL) {
+		entry->first = left->start;
+		entry->last = entry->end;
+		entry->free_down = entry->start - left->last;
+		return;
+	}
+	entry->first = left->first;
+	entry->last = right->last;
+	entry->free_down = MAX(
+	    MAX(left->free_down, entry->start - left->last),
+	    MAX(right->free_down, right->first - entry->end));
 }
 
 RB_GENERATE(iommu_gas_entries_tree, iommu_map_entry, rb_entry,