From c87f2285d0f94bbb594c2d768143e2569697df02 Mon Sep 17 00:00:00 2001
From: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Date: Mon, 18 Sep 2017 16:51:51 +0200
Subject: [PATCH] s390/mm: fix write access check in gup_huge_pmd()

commit ba385c0594e723d41790ecfb12c610e6f90c7785 upstream.

The check for the _SEGMENT_ENTRY_PROTECT bit in gup_huge_pmd() is the
wrong way around. It must not be set for write==1, and not be checked for
write==0. Fix this similar to how it was fixed for ptes long time ago in
commit 25591b070336 ("[S390] fix get_user_pages_fast").

One impact of this bug would be unnecessarily using the gup slow path for
write==0 on r/w mappings. A potentially more severe impact would be that
gup_huge_pmd() will succeed for write==1 on r/o mappings.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
[bwh: Backported to 3.2:
 - Segment flag names are different
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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