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Work to update this page for F12 has only just begun. You can see a copy of the F11 page here.


Virtualization in Fedora 12 includes major changes, and new features, that continue to support KVM, Xen, and many other virtual machine platforms.

KVM and qemu have gained a number of new features in this release. KVM guest memory usage and performance is improved by the addition of KSM and KVM Huge Page Backed Memory. The performance of the qcow2 image format is greatly improved. Support for both SR-IOV and NIC hotplug has been added. Finally, gPXE is now used in place of etherboot for guest PXE booting.

On the libvirt side, APIs have been added for storage management and network interface management. libvirt now also runs qemu processes unprivileged.

A new library (libguestfs) and an interactive tool (guestfish) is now available for accessing and modifying virtual machine disk images.

Kernel SamePage Merging and Reduced Guest Memory Usage

KSM (Kernel SamePage Merging) allows identical memory pages to be merged by the kernel into a single page shared between one or more processes. This feature is leveraged by KVM to allow multiple, similar, guest virtual machines to have a reduced memory footprint. Because memory is shared, the combined memory usage of the guests is reduced.

KVM Huge Page Backed Memory

Enable KVM guests to use huge page backed memory in order to reduce memory consumption and improve performance by reducing CPU cache pressure. Users of KVM guests using huge page backed memory should experience improved performance with some savings in host memory consumption. The performance benefit is workload dependent.Using huge pages for guest memory does have a downside, however - you can no longer swap nor balloon guest memory.

KVM NIC Hotplug

  • KVM NIC Hotplug - Allow the addition of a guest network interface (NIC) a guest virtual machine without needing to restart the guest.

KVM qcow2 Performance

  • KVM qcow2 Performance - Improve the I/O performance of virtual machines using disk images in the qcow2 image format.

KVM Stable Guest ABI

  • KVM Stable Guest ABI - Allow guest virtual machines to be presented with the same application binary interface across QEMU upgrades.

libguestfs library for accessing and modifying virtual machines

  • libguestfs - A library for accessing and modifying virtual machine disk images. guestfish is an interactive shell tool for editing virtual machine disk images. Technically, this actually launched in F11, but not as a "Feature"[1].

Network Interface Management

  • Network Interface Management - Provide tools to easily set up commonly used network configurations, like bridges, bonds, vlan's and sensible combinations thereof, in particular for virtualized hosts.

Single Root I/O Virtualization

  • SR-IOV - Single Root I/O Virtualization (SR-IOV) is a PCI feature which allows virtual functions (VF) to be created that share the resources of a physical function (PF).


  • VirtgPXE - Replace the deprecated etherboot pxe booting infrastructure with the more modern and currently upstream supported gpxe.

Virt Privileges

  • Virt Privileges - Improve security by adjusting the privileges of QEMU processes managed by libvirt. Also, allow KVM to be used by unprivileged users.

Virt Storage Management

Other Improvements

Libvirt Technology Compatibility Kit

Xen Kernel Support

The kernel package in Fedora 12 supports booting as a guest domU, but will not function as a dom0 until such support is provided upstream. Work is ongoing and hopes are high that support will be included in kernel 2.6.30 and Fedora 12.

The most recent Fedora release with dom0 support is Fedora 8.

Booting a Xen domU guest within a Fedora 12 host requires the KVM based xenner. Xenner runs the guest kernel and a small Xen emulator together as a KVM guest.

KVM requires hardware virtualization features in the host system.
Systems lacking hardware virtualization do not support Xen guests at this time.

For more information refer to: