s390: Optimize __pa/__va when RANDOMIZE_IDENTITY_BASE is off

Use a zero identity base when CONFIG_RANDOMIZE_IDENTITY_BASE is off,
slightly optimizing __pa/__va calculations.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/boot/startup.c

@@ -372,8 +372,9 @@ static unsigned long setup_kernel_memory_layout(unsigned long kernel_size)
 	BUILD_BUG_ON(MAX_DCSS_ADDR > (1UL << MAX_PHYSMEM_BITS));
 	max_mappable = max(ident_map_size, MAX_DCSS_ADDR);
 	max_mappable = min(max_mappable, vmemmap_start);
-	if (IS_ENABLED(CONFIG_RANDOMIZE_IDENTITY_BASE))
-		__identity_base = round_down(vmemmap_start - max_mappable, rte_size);
+#ifdef CONFIG_RANDOMIZE_IDENTITY_BASE
+	__identity_base = round_down(vmemmap_start - max_mappable, rte_size);
+#endif
 	boot_debug("identity map:        0x%016lx-0x%016lx\n", __identity_base,
 		   __identity_base + ident_map_size);
 

arch/s390/include/asm/page.h

@@ -184,7 +184,11 @@ extern struct vm_layout vm_layout;
 
 #define __kaslr_offset		vm_layout.kaslr_offset
 #define __kaslr_offset_phys	vm_layout.kaslr_offset_phys
+#ifdef CONFIG_RANDOMIZE_IDENTITY_BASE
 #define __identity_base		vm_layout.identity_base
+#else
+#define __identity_base		0UL
+#endif
 #define ident_map_size		vm_layout.identity_size
 
 static inline unsigned long kaslr_offset(void)

arch/s390/kernel/setup.c

@@ -740,7 +740,7 @@ static void __init reserve_lowcore(void)
 	void *lowcore_end = lowcore_start + sizeof(struct lowcore);
 	void *start, *end;
 
-	if ((void *)__identity_base < lowcore_end) {
+	if (absolute_pointer(__identity_base) < lowcore_end) {
 		start = max(lowcore_start, (void *)__identity_base);
 		end = min(lowcore_end, (void *)(__identity_base + ident_map_size));
 		memblock_reserve(__pa(start), __pa(end));