diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
index 64bd7ac3e35d1..f8d0550e5d2af 100644
--- a/arch/s390/boot/startup.c
+++ b/arch/s390/boot/startup.c
@@ -176,6 +176,7 @@ static unsigned long setup_kernel_memory_layout(void)
 	unsigned long asce_limit;
 	unsigned long rte_size;
 	unsigned long pages;
+	unsigned long vsize;
 	unsigned long vmax;
 
 	pages = ident_map_size / PAGE_SIZE;
@@ -183,11 +184,9 @@ static unsigned long setup_kernel_memory_layout(void)
 	vmemmap_size = SECTION_ALIGN_UP(pages) * sizeof(struct page);
 
 	/* choose kernel address space layout: 4 or 3 levels. */
-	vmemmap_start = round_up(ident_map_size, _REGION3_SIZE);
-	if (IS_ENABLED(CONFIG_KASAN) ||
-	    vmalloc_size > _REGION2_SIZE ||
-	    vmemmap_start + vmemmap_size + vmalloc_size + MODULES_LEN >
-		    _REGION2_SIZE) {
+	vsize = round_up(ident_map_size, _REGION3_SIZE) + vmemmap_size + MODULES_LEN;
+	vsize = size_add(vsize, vmalloc_size);
+	if (IS_ENABLED(CONFIG_KASAN) || (vsize > _REGION2_SIZE)) {
 		asce_limit = _REGION1_SIZE;
 		rte_size = _REGION2_SIZE;
 	} else {