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
Git-commit: d6df52e9996dcc2062c3d9c9123288468bb95b52
Patch-mainline: v5.8-rc5
References: git-fixes bsc#1213825

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>
Acked-by: Miroslav Franc <mfranc@suse.cz>
---
 arch/s390/mm/maccess.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/s390/mm/maccess.c b/arch/s390/mm/maccess.c
index 22a0be655f27..1d17413b319a 100644
--- a/arch/s390/mm/maccess.c
+++ b/arch/s390/mm/maccess.c
@@ -62,11 +62,15 @@ void notrace 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(dst, src, size);
-		dst += copied;
-		src += copied;
-		size -= copied;
+	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;
+		}
 	}
 	spin_unlock_irqrestore(&s390_kernel_write_lock, flags);
 }