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2.46. xen

Xen is a high-performance and secure open-source virtualization framework. The virtualization allows users to run guest operating systems in virtual machines on top of a host operating system.
  • In some cases, Red Hat Enterprise Linux 6 guests running fully-virtualized under Red Hat Enterprise Linux 5 experience a time drift or fail to boot. In some cases, drifting may start after migration of the virtual machine to a host with different speed. This is due to limitations in the Red Hat Enterprise Linux 5 Xen Hypervisor. To work around this, add clocksource=acpi_pm or clocksource=jiffies to the kernel command line for the guest. Alternatively, if running under Red Hat Enterprise Linux 5.7 or newer, locate the guest configuration file for the guest and add the hpet=0 option in it.
  • There are only 2 virtual slots (00:06.0 and 00:07.0) that are available for hot plug support in a virtual guest. (BZ#564261)
  • 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 behavior is required, disable pci-dev-assign-strict-check in /etc/xen/xend-config.sxp. (BZ#508310)
  • 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)
  • 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 known issues applies to the Intel 64 and AMD64 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)
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