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@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From f094a39c6ba168f2df1edfd1731cca377af5f442 Mon Sep 17 00:00:00 2001
From: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx
Fixes: c929500d7a5a ("s390/nmi: s390: New low level handling for machine check happening in guest")
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
Reviewed-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
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
