releases/4.14.308/s390-maccess-add-no-dat-mode-to-kernel_write.patch

From d6df52e9996dcc2062c3d9c9123288468bb95b52 Mon Sep 17 00:00:00 2001
From: Vasily Gorbik <gor@linux.ibm.com>
Date: Wed, 24 Jun 2020 17:39:14 +0200
Subject: s390/maccess: add no DAT mode to kernel_write

From: Vasily Gorbik <gor@linux.ibm.com>

commit d6df52e9996dcc2062c3d9c9123288468bb95b52 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/s390/mm/maccess.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

--- a/arch/s390/mm/maccess.c
+++ b/arch/s390/mm/maccess.c
@@ -58,13 +58,19 @@ static notrace long s390_kernel_write_od
  */
 void notrace s390_kernel_write(void *dst, const void *src, size_t size)
 {
+	unsigned long flags;
 	long copied;
 
-	while (size) {
-		copied = s390_kernel_write_odd(dst, src, size);
-		dst += copied;
-		src += copied;
-		size -= copied;
+	flags = arch_local_save_flags();
+	if (!(flags & PSW_MASK_DAT)) {
+		memcpy(dst, src, size);
+	} else {
+		while (size) {
+			copied = s390_kernel_write_odd(dst, src, size);
+			dst += copied;
+			src += copied;
+			size -= copied;
+		}
 	}
 }