s390/maccess: add no DAT mode to kernel_write

To be able to patch kernel code before paging is initialized do plain
memcpy if DAT is off. This is required to enable early jump label
initialization.
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/mm/maccess.c

@@ -62,12 +62,16 @@ notrace void *s390_kernel_write(void *dst, const void *src, size_t size)
 	long copied;
 
 	spin_lock_irqsave(&s390_kernel_write_lock, flags);
+	if (!(flags & PSW_MASK_DAT)) {
+		memcpy(dst, src, size);
+	} else {
 		while (size) {
 			copied = s390_kernel_write_odd(tmp, src, size);
 			tmp += copied;
 			src += copied;
 			size -= copied;
 		}
+	}
 	spin_unlock_irqrestore(&s390_kernel_write_lock, flags);
 
 	return dst;