Re: [PATCH] KVM: s390: vsie: Fix the initialization of the epoch extension (epdx) field

[Christian Borntraeger]

Am 23.11.22 um 10:08 schrieb Thomas Huth:
> We recently experienced some weird huge time jumps in nested guests when
> rebooting them in certain cases. After adding some debug code to the epoch
> handling in vsie.c (thanks to David Hildenbrand for the idea!), it was
> obvious that the "epdx" field (the multi-epoch extension) did not get set
> to 0xff in case the "epoch" field was negative.
> Seems like the code misses to copy the value from the epdx field from
> the guest to the shadow control block. By doing so, the weird time
> jumps are gone in our scenarios.
>
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2140899
> Fixes: 8fa1696ea781 ("KVM: s390: Multiple Epoch Facility support")

We might want to add cc stable, just in case.

Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>


> Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
> ---
>   arch/s390/kvm/vsie.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 94138f8f0c1c..ace2541ababd 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -546,8 +546,10 @@ static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>   	if (test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_CEI))
>   		scb_s->eca |= scb_o->eca & ECA_CEI;
>   	/* Epoch Extension */
> -	if (test_kvm_facility(vcpu->kvm, 139))
> +	if (test_kvm_facility(vcpu->kvm, 139)) {
>   		scb_s->ecd |= scb_o->ecd & ECD_MEF;
> +		scb_s->epdx = scb_o->epdx;
> +	}
>   
>   	/* etoken */
>   	if (test_kvm_facility(vcpu->kvm, 156))