Chapter 62. Virtualization

Migration of certain guests from Red Hat Enterprise Linux 7.2 to 7.3 hosts is not possible

Prior to this update, the PCI address of any USB controller that did not have an explicitly specified model value was ignored on IBM Power guest virtual machines. This bug has been fixed, but as a consequence of the fix, it is not possible to perform a live migration of guests that use the described USB controllers from a Red Hat Enterprise Linux 7.2 host to a Red Hat Enterprise Linux 7.3 host, due to the different PCI addresses of the USB controller.
To work around this problem, edit the guest XML file and add a model attribute with the pci-ohci value to the USB <controller> element, for example as follows:
<controller type='usb' model='pci-ohci' index='0'>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
</controller>
Afterwards, shut down the guest and start it again for the changes to take effect. As a result, the guest can be migrated from Red Hat Enterprise Linux 7.2 to 7.3. (BZ#1357468)

numad changes QEMU memory bindings

Currently, the numad daemon cannot distinguish between memory bindings that numad sets and memory bindings set explicitly by the memory mappings of a process. As a consequence, numad changes QEMU memory bindings, even when the NUMA memory policy is specified in the QEMU command line. To work around this problem, if manual NUMA bindings are specified in the guest, disable numad. This ensures that manual bindings configured in virtual machines are not changed by numad. (BZ#1360584)

Memory usage for QEMU processes is shown without mapped hugetlbfs pages

Mapped hugetlbfs pages are not accounted for by the kernel when calculating process memory usage. As a consequence, commands such as top and ps show memory usage for QEMU processes without the mapped hugetlbfs pages when a virtual machine is configured to use huge pages. (BZ#1221443)

qemu-kvm below version 2.6.0 cannot load 2.88 MB floppy disks

When using the qemu-kvm package below version 2.6.0, KVM guests are not able to load a 2.88 MB floppy disk if it is inserted after the guest has already booted up. To work around this problem, insert the floppy disk before booting the guest, or use qemu-kvm version 2.6.0 or later. (BZ#1209707)