On Wed, 23 Nov 2022 10:08:33 +0100 Thomas Huth <thuth@xxxxxxxxxx> wrote: > 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: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> > --- > 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; looks quite straightforward > + } > > /* etoken */ > if (test_kvm_facility(vcpu->kvm, 156))
