The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 1ea1d6a847d2b1d17fefd9196664b95f052a0775 Mon Sep 17 00:00:00 2001 From: Christian Borntraeger borntraeger@linux.ibm.com Date: Thu, 13 Jan 2022 11:44:19 +0100 Subject: [PATCH] s390/nmi: handle guarded storage validity failures for KVM guests
machine check validity bits reflect the state of the machine check. If a guest does not make use of guarded storage, the validity bit might be off. We can not use the host CR bit to decide if the validity bit must be on. So ignore "invalid" guarded storage controls for KVM guests in the host and rely on the machine check being forwarded to the guest. If no other errors happen from a host perspective everything is fine and no process must be killed and the host can continue to run.
Cc: stable@vger.kernel.org Fixes: c929500d7a5a ("s390/nmi: s390: New low level handling for machine check happening in guest") Reported-by: Carsten Otte cotte@de.ibm.com Signed-off-by: Christian Borntraeger borntraeger@linux.ibm.com Tested-by: Carsten Otte cotte@de.ibm.com Reviewed-by: Heiko Carstens hca@linux.ibm.com Signed-off-by: Heiko Carstens hca@linux.ibm.com
diff --git a/arch/s390/kernel/nmi.c b/arch/s390/kernel/nmi.c index 0c9e894913dc..147c0d5fd9b4 100644 --- a/arch/s390/kernel/nmi.c +++ b/arch/s390/kernel/nmi.c @@ -307,11 +307,21 @@ static int notrace s390_validate_registers(union mci mci, int umode) if (cr2.gse) { if (!mci.gs) { /* - * Guarded storage register can't be restored and - * the current processes uses guarded storage. - * It has to be terminated. + * 2 cases: + * - machine check in kernel or userspace + * - machine check while running SIE (KVM guest) + * For kernel or userspace the userspace values of + * guarded storage control can not be recreated, the + * process must be terminated. + * For SIE the guest values of guarded storage can not + * be recreated. This is either due to a bug or due to + * GS being disabled in the guest. The guest will be + * notified by KVM code and the guests machine check + * handling must take care of this. The host values + * are saved by KVM and are not affected. */ - kill_task = 1; + if (!test_cpu_flag(CIF_MCCK_GUEST)) + kill_task = 1; } else { load_gs_cb((struct gs_cb *)mcesa->guarded_storage_save_area); }