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5.29. xen

  • There are only 2 virtual slots (00:06.0 and 00:07.0) that are available for hotplug support in a virtual guest.
  • As of Red Hat Enterprise Linux 5.4, PCI devices connected to a single PCI-PCI bridge can no longer be assigned to different PV guests. If the old, unsafe behaviour is required, disable pci-dev-assign-strict-check in /etc/xen/xend-config.sxp. (BZ#508310)
  • In live migrations of paravirtualized guests, time-dependent guest processes may function improperly if the corresponding hosts' (dom0) times are not synchronized. Use NTP to synchronize system times for all corresponding hosts before migration. (BZ#426861)
  • When running x86_64 Xen, it is recommended to set dom0-min-mem in /etc/xen/xend-config.sxp to a value of 1024 or higher. Lower values may cause the dom0 to run out of memory, resulting in poor performance or out-of-memory situations. (BZ#519492)
  • The Red Hat Enterprise Linux 3 kernel does not include SWIOTLB support. SWIOTLB support is required for Red Hat Enterprise Linux 3 guests to support more than 4GB of memory on AMD Opteron and Athlon-64 processors. Consequently, Red Hat Enterprise Linux 3 guests are limited to 4GB of memory on AMD processors. (BZ#504187)
  • When setting up interface bonding on dom0, the default network-bridge script may cause bonded network interfaces to alternately switch between unavailable and available. This occurrence is commonly known as flapping.
    To prevent this, replace the standard network-script line in /etc/xen/xend-config.sxp with the following line: 
    			
(network-script network-bridge-bonding netdev=bond0)
    Doing so will disable the netloop device, which prevents Address Resolution Protocol (ARP) monitoring from failing during the address transfer process. (BZ#429154, BZ#429154)
  • The Hypervisor outputs messages regarding attempts by any guest to write to an MSR. Such messages contain the statement Domain attempted WRMSR. These messages can be safely ignored; furthermore, they are rate limited and should pose no performance risk. (BZ#477647)
The following note applies to x86_64 Architectures:
  • Installing Red Hat Enterprise Linux 3.9 on a fully virtualized guest may be extremely slow. In addition, booting up the guest after installation may result in hda: lost interrupt errors.
    To avoid this bootup error, configure the guest to use the SMP kernel. (BZ#249521)