linux-kernel - [PATCH v1 1/1] KVM: s390: Fix missing present bit for gmap puds

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Message-ID: <20251028130150.57379-2-imbrenda@linux.ibm.com>
Date: Tue, 28 Oct 2025 14:01:50 +0100
From: Claudio Imbrenda <imbrenda@...ux.ibm.com>
To: akpm@...ux-foundation.org
Cc: balbirs@...dia.com, borntraeger@...ibm.com, david@...hat.com,
        Liam.Howlett@...cle.com, airlied@...il.com, apopple@...dia.com,
        baohua@...nel.org, baolin.wang@...ux.alibaba.com, byungchul@...com,
        dakr@...nel.org, dev.jain@....com, dri-devel@...ts.freedesktop.org,
        francois.dugast@...el.com, gourry@...rry.net, joshua.hahnjy@...il.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        lorenzo.stoakes@...cle.com, lyude@...hat.com, matthew.brost@...el.com,
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        kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-next@...r.kernel.org, hca@...ux.ibm.com, gor@...ux.ibm.com,
        agordeev@...ux.ibm.com
Subject: [PATCH v1 1/1] KVM: s390: Fix missing present bit for gmap puds

For hugetlbs, gmap puds have the present bit set. For normal puds
(which point to ptes), the bit is not set. This is in contrast to the
normal userspace puds, which always have the bit set for present pmds.

This causes issues when ___pte_offset_map() is modified to only check
for the present bit.

The solution to the problem is simply to always set the present bit for
present gmap pmds.

Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Link: https://lore.kernel.org/lkml/20251017144924.10034-1-borntraeger@linux.ibm.com/
Tested-by: Christian Borntraeger <borntraeger@...ux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@...ux.ibm.com>
---
 arch/s390/mm/gmap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 8ff6bba107e8..22c448b32340 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -599,8 +599,9 @@ int __gmap_link(struct gmap *gmap, unsigned long gaddr, unsigned long vmaddr)
 					| _SEGMENT_ENTRY_GMAP_UC
 					| _SEGMENT_ENTRY;
 			} else
-				*table = pmd_val(*pmd) &
-					_SEGMENT_ENTRY_HARDWARE_BITS;
+				*table = (pmd_val(*pmd) &
+					_SEGMENT_ENTRY_HARDWARE_BITS)
+					| _SEGMENT_ENTRY;
 		}
 	} else if (*table & _SEGMENT_ENTRY_PROTECT &&
 		   !(pmd_val(*pmd) & _SEGMENT_ENTRY_PROTECT)) {
-- 
2.51.0