From: Thomas Huth <thuth@xxxxxxxxxx> commit 0dd4cdccdab3d74bd86b868768a7dca216bcce7e upstream. 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") Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx> Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx> Acked-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx # 4.19+ Link: https://lore.kernel.org/r/20221123090833.292938-1-thuth@xxxxxxxxxx Message-Id: <20221123090833.292938-1-thuth@xxxxxxxxxx> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/s390/kvm/vsie.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/arch/s390/kvm/vsie.c +++ b/arch/s390/kvm/vsie.c @@ -538,8 +538,10 @@ static int shadow_scb(struct kvm_vcpu *v 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))
