A thread on the OpenBSD -misc mailing list began by discussing whether or not XEN had been ported to OpenBSD, "is it planned at some point to release a paravirtualized xen kernel for OpenBSD 4.3 or 4.4?" Later in the discussion it was suggested that virtualization should be a priority for security reasons, "virtualization seems to have a lot of security benefits." OpenBSD creator Theo de Raadt strongly disagreed with this assertion, "you've been smoking something really mind altering, and I think you should share it." He went on to describe virtualization as "something on the shelf, [which] has all sorts of pretty colours, and you've bought it", explaining:
"x86 virtualization is about basically placing another nearly full kernel, full of new bugs, on top of a nasty x86 architecture which barely has correct page protection. Then running your operating system on the other side of this brand new pile of shit. You are absolutely deluded, if not stupid, if you think that a worldwide collection of software engineers who can't write operating systems or applications without security holes, can then turn around and suddenly write virtualization layers without security holes."
Later in the thread, Theo went on to note, "if the actual hardware let us do more isolation than we do today, we would actually do it in our operating system. The problem is the hardware DOES NOT actually give us more isolation abilities, therefore the VM does not actually do anything what the say they do." He then suggested that companies marketing virtualization should soften their claims to something supportable, such as, "yes, it [increases] hardware utilization, and the nasty security impact might be low".
A new feature that will first be availble in the upcoming 2.6.20 kernel is KVM, a Kernel-based Virtual Machine. The project's webpage describes KVM as, "a full virtualization solution for Linux on x86 hardware. It consists of a loadable kernel module (kvm.ko) and a userspace component. Using KVM, one can run multiple virtual machines running unmodified Linux or Windows images. Each virtual machine has private virtualized hardware: a network card, disk, graphics adapter, etc." The project's FAQ explains that the functionality requires "an x86 machine running a recent Linux kernel on an Intel processor with VT (virtualization technology) extensions, or an AMD processor with SVM extensions (also called AMD-V)." The userland aspect of KVM is a slighlty modified version of qemu, used to instantiate the virtual machine.
Ingo Molnar [interview] announced a new patch introducing paravirtualization support for KVM, outdating the KVM FAQ which in comparing KVM to Xen notes, "Xen supports both full virtualization and a technique called paravirtualization, which allows better performance for modified guests. kvm does not at present support paravirtualization." In describing his patch which is against the 2.6.20-rc3 + KVM trunk kernel, Ingo said it, "includes support for the hardware cr3-cache feature of Intel-VMX CPUs. (which speeds up context switches and TLB flushes)". He went on to add, "some aspects of the code are still a bit ad-hoc and incomplete, but the code is stable enough in my testing and i'd like to have some feedback." In a series of benchmarks, he found 2-task context switch performance to be improved by a factor of four, while "hackbench 1" showed twice as good performance, and "hackbench 5" showed a 30% improvement. His email goes on to detail how the paravirtualization works.