From a2c5764076615b660846a14ccad8cdb5ac2e2975 Mon Sep 17 00:00:00 2001 From: Thomas Huth Date: Wed, 23 Nov 2022 10:08:33 +0100 Subject: [PATCH] KVM: s390: vsie: Fix the initialization of the epoch extension (epdx) field commit 015871b0edc3aa114e7bac8a9f2ee3079acb1909 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: e1688250bd65 ("KVM: s390: Multiple Epoch Facility support") Signed-off-by: Thomas Huth Reviewed-by: Christian Borntraeger Acked-by: David Hildenbrand Reviewed-by: Claudio Imbrenda Reviewed-by: Janosch Frank Cc: stable@vger.kernel.org # 4.19+ Link: https://lore.kernel.org/r/20221123090833.292938-1-thuth@redhat.com Message-Id: <20221123090833.292938-1-thuth@redhat.com> Signed-off-by: Janosch Frank Signed-off-by: Greg Kroah-Hartman --- 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 4f6c22d72072a..2021946176de8 100644 --- a/arch/s390/kvm/vsie.c +++ b/arch/s390/kvm/vsie.c @@ -540,8 +540,10 @@ 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)) -- 2.39.5