In order to bring up RHEL6 virtio devices for a vm we are currently using the kubevirt.io/placePCIDevicesOnRootComplex in order to use the legacy virtio block drivers which are available in RHEL6. There is no support for this in CNV 1.4

kubevirt template:
apiVersion: kubevirt.io/v1alpha3
kind: VirtualMachine
metadata:
labels:
kubevirt.io/vm: %HOST%
name: %HOST%
namespace: virtualmachines
spec:
dataVolumeTemplates:

• metadata:
  annotations:
  kubevirt.io/provisionOnNode: %NODE%
  creationTimestamp: null
  name: mybuild6v10-os
  spec:
  pvc:
  accessModes:
• ReadWriteOnce
  resources:
  requests:
  storage: 25Gi
  storageClassName: kubevirt-hostpath-provisioner
  source:
  blank: {}
  status: {}
  running: true
  template:
  metadata:
  annotations:
  kubevirt.io/placePCIDevicesOnRootComplex: "true"
  creationTimestamp: null
  labels:
  kubevirt.io/vm: %HOST%
  spec:
  domain:
  cpu:
  cores: 2
  model: host-passthrough
  sockets: 2
  threads: 1
  devices:
  disks:
• bootOrder: 2
  disk:
  bus: virtio
  pciAddress: "0000:00:03.0"
  name: os-disk
  interfaces:
• bootOrder: 1
  bridge: {}
  macAddress: %MAC%
  name: vnic0
  networkInterfaceMultiqueue: true
  features:
  acpi:
  enabled: true
  machine:
  type: ""
  resources:
  requests:
  cpu: "3"
  memory: 16Gi
  networks:
• multus:
  networkName: vlan0
  name: vnic0
  terminationGracePeriodSeconds: 10
  volumes:
• dataVolume:
  name: mybuild6v10-os
  name: os-disk
  —
  This results in something like:
  virsh # dumpxml virtualmachines_mybuild6v10.etc.test.domain
  <domain type='kvm' id='1'>
  <name>virtualmachines_mybuild6v10.etc.test.domain</name>
  <uuid>228d4450-5ccc-11fa-b0f0-0050666d427d</uuid>
  <metadata>
  <kubevirt xmlns="http://kubevirt.io">
  <uid>edf29e4c-0ed8-11eb-a8f0-f04da20b8666</uid>
  <graceperiod>
  <deletionGracePeriodSeconds>10</deletionGracePeriodSeconds>
  </graceperiod>
  </kubevirt>
  </metadata>
  <memory unit='KiB'>16777216</memory>
  <currentMemory unit='KiB'>16777216</currentMemory>
  <vcpu placement='static'>4</vcpu>
  <iothreads>1</iothreads>
  <resource>
  <partition>/machine</partition>
  </resource>
  <sysinfo type='smbios'>
  <system>
  <entry name='uuid'>228d4450-5ccc-11fa-b0f0-0050666d427d</entry>
  </system>
  </sysinfo>
  <os>
  <type arch='x86_64' machine='pc-q35-rhel7.6.0'>hvm</type>
  </os>
  <features>
  <acpi/>
  </features>
  <cpu mode='host-passthrough' check='none'>
  <topology sockets='2' cores='2' threads='1'/>
  </cpu>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
  <emulator>/usr/libexec/qemu-kvm</emulator>
  <disk type='file' device='disk'>
  <driver name='qemu' type='raw' cache='none' queues='3'/>
  <source file='/var/run/kubevirt-private/vmi-disks/os-disk/disk.img'/>
  <backingStore/>
  <target dev='vda' bus='virtio'/>
  <boot order='2'/>
  <alias name='ua-os-disk'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
  </disk>
  <controller type='usb' index='0' model='none'>
  <alias name='usb'/>
  </controller>
  <controller type='sata' index='0'>
  <alias name='ide'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
  </controller>
  <controller type='pci' index='0' model='pcie-root'>
  <alias name='pcie.0'/>
  </controller>
  <controller type='virtio-serial' index='0'>
  <alias name='virtio-serial0'/>
  <address type='pci' domain='0x0000' bus='0x02' slot='0x00' function='0x0'/>
  </controller>
  <controller type='pci' index='1' model='pcie-root-port'>
  <model name='pcie-root-port'/>
  <target chassis='1' port='0x10'/>
  <alias name='pci.1'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0' multifunction='on'/>
  </controller>
  <controller type='pci' index='2' model='pcie-root-port'>
  <model name='pcie-root-port'/>
  <target chassis='2' port='0x11'/>
  <alias name='pci.2'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x1'/>
  </controller>
  <controller type='pci' index='3' model='pcie-root-port'>
  <model name='pcie-root-port'/>
  <target chassis='3' port='0x12'/>
  <alias name='pci.3'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x2'/>
  </controller>
  <interface type='bridge'>
  <mac address='fe:f1:f0:de:ad:bf'/>
  <source bridge='k6t-net1'/>
  <target dev='vnet0'/>
  <model type='virtio'/>
  <driver name='vhost' queues='3'/>
  <mtu size='1500'/>
  <boot order='1'/>
  <alias name='ua-vnic0'/>
  <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
  </interface>
  <serial type='unix'>
  <source mode='bind' path='/var/run/kubevirt-private/edf29e4c-0ed8-11eb-a8f0-f04da20b8666/virt-serial0'/>
  <target type='isa-serial' port='0'>
  <model name='isa-serial'/>
  </target>
  <alias name='serial0'/>
  </serial>
  <console type='unix'>
  <source mode='bind' path='/var/run/kubevirt-private/edf29e4c-0ed8-11eb-a8f0-f04da20b8666/virt-serial0'/>
  <target type='serial' port='0'/>
  <alias name='serial0'/>
  </console>
  <channel type='unix'>
  <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/domain-1-virtualmachines_myb/org.qemu.guest_agent.0'/>
  <target type='virtio' name='org.qemu.guest_agent.0' state='disconnected'/>
  <alias name='channel0'/>
  <address type='virtio-serial' controller='0' bus='0' port='1'/>
  </channel>
  <input type='mouse' bus='ps2'>
  <alias name='input0'/>
  </input>
  <input type='keyboard' bus='ps2'>
  <alias name='input1'/>
  </input>
  <graphics type='vnc' socket='/var/run/kubevirt-private/edf29e4c-0ed8-11eb-a8f0-f04da20b8666/virt-vnc'>
  <listen type='socket' socket='/var/run/kubevirt-private/edf29e4c-0ed8-11eb-a8f0-f04da20b8666/virt-vnc'/>
  </graphics>
  <video>
  <model type='vga' vram='16384' heads='1' primary='yes'/>
  <alias name='video0'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
  </video>
  <memballoon model='none'/>
  </devices>
  <seclabel type='dynamic' model='dac' relabel='yes'>
  <label>+107:+107</label>
  <imagelabel>+107:+107</imagelabel>
  </seclabel>
  </domain>
  —
  the system fails to boot or find the virtio drive