s390/maccess: add no DAT mode to kernel_write

[ Upstream commit d6df52e ]

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 <[email protected]>
Signed-off-by: Vasily Gorbik <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: Vasily Gorbik

arch/s390/mm/maccess.c

@@ -62,11 +62,15 @@ notrace void *s390_kernel_write(void *dst, const void *src, size_t size)
 	long copied;
 
 	spin_lock_irqsave(&s390_kernel_write_lock, flags);
-	while (size) {
-		copied = s390_kernel_write_odd(tmp, src, size);
-		tmp += copied;
-		src += copied;
-		size -= copied;
+	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);