From: Claudio Imbrenda <imbrenda@linux.ibm.com>
Date: Tue, 2 Jun 2026 14:23:48 +0000 (+0200)
Subject: KVM: s390: Fix _gmap_crstep_xchg_atomic()
X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=d1adc098ce08893c92fce3db63f7bb750fbb4c30;p=thirdparty%2Fkernel%2Flinux.git

KVM: s390: Fix _gmap_crstep_xchg_atomic()

The previous incorrect behaviour cleared the vsie_notif bit without
returning false, which allowed shadow crstes to be installed without
the vsie_notif bit.

Return false and do not perform the operation if an unshadow event has
been triggered, but still attempt to clear the vsie_notif bit from the
existing crste.

This will prevent the installation of shadow crstes without vsie_notif
bit and will also prevent the caller from looping forever if it was
not checking for the sg->invalidated flag.

Fixes: b827ef02f409 ("KVM: s390: Remove non-atomic dat_crstep_xchg()")
Fixes: a2c17f9270cc ("KVM: s390: New gmap code")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260602142356.169458-3-imbrenda@linux.ibm.com>
---

diff --git a/arch/s390/kvm/gmap.h b/arch/s390/kvm/gmap.h
index 742e42a31744..5374f21aaf8d 100644
--- a/arch/s390/kvm/gmap.h
+++ b/arch/s390/kvm/gmap.h
@@ -273,11 +273,14 @@ static inline bool __must_check _gmap_crstep_xchg_atomic(struct gmap *gmap, unio
 		gmap_unmap_prefix(gmap, gfn, gfn + align);
 	}
 	if (crste_leaf(oldcrste) && crste_needs_unshadow(oldcrste, newcrste)) {
+		newcrste = oldcrste;
 		newcrste.s.fc1.vsie_notif = 0;
 		if (needs_lock)
 			gmap_handle_vsie_unshadow_event(gmap, gfn);
 		else
 			_gmap_handle_vsie_unshadow_event(gmap, gfn);
+		dat_crstep_xchg_atomic(crstep, oldcrste, newcrste, gfn, gmap->asce);
+		return false;
 	}
 	if (!oldcrste.s.fc1.d && newcrste.s.fc1.d && !newcrste.s.fc1.s)
 		SetPageDirty(phys_to_page(crste_origin_large(newcrste)));