linux-kernel - [PATCH v1 2/3] KVM: s390: vsie: Fix race in walk_guest

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Message-ID: <20260206143553.14730-3-imbrenda@linux.ibm.com>
Date: Fri,  6 Feb 2026 15:35:52 +0100
From: Claudio Imbrenda <imbrenda@...ux.ibm.com>
To: kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, nsg@...ux.ibm.com,
        nrb@...ux.ibm.com, seiden@...ux.ibm.com, gra@...ux.ibm.com,
        schlameuss@...ux.ibm.com, hca@...ux.ibm.com, svens@...ux.ibm.com,
        agordeev@...ux.ibm.com, gor@...ux.ibm.com, david@...nel.org,
        gerald.schaefer@...ux.ibm.com
Subject: [PATCH v1 2/3] KVM: s390: vsie: Fix race in walk_guest_tables()

It is possible that walk_guest_tables() is called on a shadow gmap that
has been removed already, in which case its parent will be NULL.

In such case, return -EAGAIN and let the callers deal with it.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
---
 arch/s390/kvm/gaccess.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 67de47a81a87..4630b2a067ea 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -1287,7 +1287,10 @@ static int walk_guest_tables(struct gmap *sg, unsigned long saddr, struct pgtwal
 	union asce asce;
 	int rc;
 
+	if (!parent)
+		return -EAGAIN;
 	kvm = parent->kvm;
+	WARN_ON(!kvm);
 	asce = sg->guest_asce;
 	entries = get_entries(w);
 
-- 
2.52.0