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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_pmorclocksource=jiffiesto 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 thehpet=0option 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 interrupterrors.To avoid this bootup error, configure the guest to use the SMP kernel. (BZ#249521)
