The patch below does not apply to the 5.4-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 f094a39c6ba168f2df1edfd1731cca377af5f442 Mon Sep 17 00:00:00 2001 From: Christian Borntraeger borntraeger@linux.ibm.com Date: Mon, 17 Jan 2022 18:40:32 +0100 Subject: [PATCH] s390/nmi: handle vector validity failures for KVM guests

The machine check validity bit tells about the context. If a KVM guest was running the bit tells about the guest validity and the host state is not affected. As a guest can disable the guest validity this might result in unwanted host errors on machine checks.

Cc: stable@vger.kernel.org Fixes: c929500d7a5a ("s390/nmi: s390: New low level handling for machine check happening in guest") Signed-off-by: Christian Borntraeger borntraeger@linux.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 147c0d5fd9b4..651a51914e34 100644 --- a/arch/s390/kernel/nmi.c +++ b/arch/s390/kernel/nmi.c @@ -264,7 +264,14 @@ static int notrace s390_validate_registers(union mci mci, int umode) /* Validate vector registers */ union ctlreg0 cr0;

- if (!mci.vr) { + /* + * The vector validity must only be checked if not running a + * KVM guest. For KVM guests the machine check is forwarded by + * KVM and it is the responsibility of the guest to take + * appropriate actions. The host vector or FPU values have been + * saved by KVM and will be restored by KVM. + */ + if (!mci.vr && !test_cpu_flag(CIF_MCCK_GUEST)) { /* * Vector registers can't be restored. If the kernel * currently uses vector registers the system is