Quoting Nico Boehr (2022-08-29 09:56:02) > When running under PV, the guest's TOD clock is under control of the > ultravisor and the hypervisor isn't allowed to change it. Hence, don't > allow userspace to change the guest's TOD clock by returning > -EOPNOTSUPP. > > When userspace changes the guest's TOD clock, KVM updates its > kvm.arch.epoch field and, in addition, the epoch field in all state > descriptions of all VCPUs. > > But, under PV, the ultravisor will ignore the epoch field in the state > description and simply overwrite it on next SIE exit with the actual > guest epoch. This leads to KVM having an incorrect view of the guest's > TOD clock: it has updated its internal kvm.arch.epoch field, but the > ultravisor ignores the field in the state description. > > Whenever a guest is now waiting for a clock comparator, KVM will > incorrectly calculate the time when the guest should wake up, possibly > causing the guest to sleep for much longer than expected. > > With this change, kvm_s390_set_tod() will now take the kvm->lock to be > able to call kvm_s390_pv_is_protected(). Since kvm_s390_set_tod_clock() > also takes kvm->lock, use __kvm_s390_set_tod_clock() instead. > > Fixes: 0f3035047140 ("KVM: s390: protvirt: Do only reset registers that are accessible") I missed a Reported-by: Marc Hartmayer <mhartmay@xxxxxxxxxxxxx> here. Sorry Marc.