The Xen virtual machine monitor was recently merged into the upcoming 2.6.23 Linux kernel in a series of patches from Jeremy Fitzhardinge. The project was originally started as a research project at the University of Cambridge, and has been repeatedly discussed as a merge candidate for the mainline Linux kernel.

Xen is described in the project's FAQ as:

"Xen is a virtual machine monitor (VMM) for x86-compatible computers. Xen can securely execute multiple virtual machines, each running its own OS, on a single physical system with close-to-native performance."

The commit diffs:

• [Add Xen interface header files]
• [Core Xen implementation]
• [virtual mmu]
• [event channels]
• [time implementation]
• [configuration]
• [add pinned page flag]
• [Complete pagetable pinning]
• [ignore RW mapping of RO pages in pagetable_init]
• [Account for stolen time]
• [Implement sched_clock]
• [SMP guest support]
• [Add support for preemption]
• [lazy-mmu operations]
• [hack to prevent bad segment register reload]
• [use the hvc console infrastructure for Xen console]
• [Add grant table support]
• [add the Xenbus sysfs and virtual device hotplug driver]
• [add virtual block device driver.]
• [add virtual network device driver]
• [machine operations]
• [handle external requests for shutdown, reboot and sysrq]
• [Place vcpu_info structure into per-cpu memory]
• [Attempt to patch inline versions of common operations]
• [suppress abs symbol warnings for unused reloc pointers]
• [use iret directly when possible]
• [disable all non-virtual drivers]