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Xen PVH Is Landing For The Linux 3.14 Kernel

Virtualization

Published on 22 January 2014 04:35 PM EST
Written by Michael Larabel in Virtualization
1 Comment

Kernel-side support for Xen PVH is landing with the Linux 3.14 kernel. The para-virtualized hardware extension support takes advantage of modern Intel and AMD CPUs.

More than one month ago I wrote of the Xen PVH support coming back up and now it's part of the Xen pull request for Linux 3.14. Xen PVH is para-virtualization that uses the CPUs's hardware extensions for faster PV support.

The Xen 3.14 pull request by Oracle's Konrad Rzeszutek Wilk explains PVH at length:
In short, PV is a mode where the kernel lets the hypervisor program page-tables, segments, etc. With EPT/NPT capabilities in current processors, the overhead of doing this in an HVM (Hardware Virtual Machine) container is much lower than the hypervisor doing it for us. In short we let a PV guest run without doing page-table, segment, syscall, etc updates through the hypervisor - instead it is all done within the guest container. It is a "hybrid" PV - hence the 'PVH' name - a PV guest within an HVM container.

The major benefits are less code to deal with - for example we only use one function from the the pv_mmu_ops (which has 39 function calls); faster performance for syscall (no context switches into the hypervisor); less traps on various operations; etc.

It is still being baked - the ABI is not yet set in stone. But it is pretty awesome and we are excited about it.
On the user-space side PVH will be supported with the Xen 4.4 release. Additional information on Xen PVH can be found via the Xen.org Wiki.

There's also event channel scalability improvements, bug-fixes, and other work as part of the Xen update for Linux 3.14.

Also submitted for the Linux 3.14 kernel merge window were the first KVM updates but there really isn't anything exciting besides bug-fixes for this alternative virtualization hypervisor.

About The Author
Michael Larabel is the principal author of Phoronix.com and founded the web-site in 2004 with a focus on enriching the Linux hardware experience and being the largest web-site devoted to Linux hardware reviews, particularly for products relevant to Linux gamers and enthusiasts but also commonly reviewing servers/workstations and embedded Linux devices. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics hardware drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated testing software. He can be followed via and or contacted via .
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