Under known issues of , we've documented a issue as quoted below. 

When you create a VM by using Red Hat Enterprise Linux (RHEL) container disk images for s390x architecture, call traces referencing virtio_balloon print to the VM console. (OCPBUGS-51113)As a workaround, add the following parameter to the VM YAML configuration: spec.autoattachMemBalloon: false.

Better we document it as below, as we now know more details about it:

When you create a s390x architecture based linux VMs, call traces referencing virtio_balloon free-page-reporting print to the VM console as free-page-reporting is broken in s390x linux kernel. (OCPBUGS-51113)As a workaround, either:

• add the following parameter to the VM YAML configuration: spec.domain.devices.autoattachMemBalloon: false to disable memory ballooning for that VM.
• add the following paramters to the KubeVirt HyperConverged CR YAML: spec.virtualMachineOptions.disableFreePageReporting: true to disable only free-page-reporting of memory ballooning for all new VMs to be created.

Please note that even in earlier documented workaround, the path of the parameter is wrong (spec.autoattachMemBalloon: false) and the correct parameter value is spec.domain.devices.autoattachMemBalloon: false