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Chapter 26. Virtualization

Coolkey does not load on Windows 7 guests

Loading the Coolkey module on Windows 7 guest virtual machines currently fails, which prevents smart card redirection from working properly on these guests. (BZ#1331471)

Disabling vCPUs on Hyper-V guests fails

Currently, it is not possible to disable CPUs on guest virtual machines running on Microsoft Hyper-V, including Microsoft Azure cloud, due to the lack of support from the host side. However, it is possible to reduce the number of online CPUs by booting guests with the nr_cpus=XX parameter passed on the kernel command line, where XX is the number of online CPUs required.
For more information, see https://access.redhat.com/solutions/2790331. (BZ#1396336)

Hot plugging hard disks as a batch on the VMware ESXi hypervisor does not work reliably

When hot plugging multiple hard disks at the same time to a Red Hat Enterprise Linux 6 guest virtual machine running on the VMware ESXi hypervisor, the host currently does not inform the guest about all of the added disks, and some of the disks thus cannot be used. To work around this problem, hot plug one hard disk at a time in the described scenario. (BZ#1224673)

Guests cannot access floppy disks larger than 1.44 MB

Guest virtual machines are currently unable to access floppy drive images larger than 1.44 MB if they are inserted while the guest is running. To work around the problem, insert the floppy drive image prior to booting the guest. (BZ#1209362)

Hyper-V guest integration services stop working after they are disabled and re-enabled

Currently, Red Hat Enterprise Linux 6 guest virtual machines running on the Microsoft Hyper-V hypervisor do not automatically restart the hyperv-daemons suite after Hyper-V guest integration services, such as data exchange and backup, are disabled and then re-enabled. As a consequence, these integration services stop working after they are disabled and re-enabled in the Hyper-V Manager interface.
To work around this problem, restart the hypervkvpd, hypervvssd, and hypervfcopyd services in the guest after re-enabling the integration services from Hyper-V Manager, or do not change the status of the integration services while the guest is running. (BZ#1121888)

Booting virtual machines with the fsgsbase and smep flags on older host CPUs fails

The fsgsbase and smep CPU flags are not properly emulated on certain older CPU models, such as the early Intel Xeon E processors. As a consequence, using fsgsbase or smep when booting a guest virtual machine on a host with such a CPU causes the boot to fail. To work around this problem, do not use fsgsbase and smep if the CPU does not support them. (BZ#1371765)

Guests with recent Windows systems in some cases fail to boot if hv_relaxed is used

Attempting to boot KVM guests with the following operating systems currently fails with an error code: 0x0000001E message if the value of the -cpu option is SandyBridge or Opteron_G4 and the hv_relaxed option is used.
  • 64-bit Windows 8 or later
  • 64-bit Windows Server 2012 or later
To work around this problem, do not use hv_relaxed. (BZ#1063124)

Limited CPU support for Windows 10 and Windows Server 2016 guests

On a Red Hat Enterprise 6 host, Windows 10 and Windows Server 2016 guests can only be created when using the following CPU models:
  • the Intel Xeon E series
  • the Intel Xeon E7 family
  • Intel Xeon v2, v3, and v4
  • Opteron G2, G3, G4, G5, and G6
For these CPU models, also make sure to set the CPU model of the guest to match the CPU model detected by running the virsh capabilities command on the host. Using the application default or hypervisor default prevents the guests from booting properly.
To be able to use Windows 10 guests on Legacy Intel Core 2 processors (also known as Penryn) or Intel Xeon 55xx and 75xx processor families (also known as Nehalem), add the following flag to the Domain XML file, with either Penryn or Nehalem as MODELNAME: 
<cpu mode='custom' match='exact'>
 <model>MODELNAME</model>
 <feature name='erms' policy='require'/>
</cpu>
Other CPU models are not supported, and both Windows 10 guests and Windows Server 2016 guests created on them are likely to become unresponsive during the boot process. (BZ#1346153)

Network connectivity not restored when vnic is enabled

If the netdev(tap) link is set to off and the vnic(virtio-net/e1000) link is set to on, network connectivity does not resume. However, if the vnic(virtio-net/e1000) link is set to off and the netdev(tap) link is set to on, network connectivity resumes.
To resolve the issue, consistently use the same device to control the link. If netdev(tap) link was set to off, using it to turn the link back on will work correctly. (BZ#1198956)

KVM guests fail to properly read physical DVD/CD-ROM media

Several problems may occur when using physical DVD/CD-ROMs with KVM guest virtual machines. To work around this problem, you can create ISO files from the physical media and use them with the virtual machines. It is recommended that you do not use physical DVD/CD-ROMs. For more information, see https://access.redhat.com/solutions/2543131. (BZ#1360581)