Over on OpenBenchmarking.org are the AMD Bulldozer Virtualization Benchmarks that provide a look at the performance overhead of using the Linux Kernel-based Virtual Machine on this platform. Ubuntu 11.10 with the Linux 3.0 kernel was used on both the host and guest with stock settings. From OpenBenchmarking.org you can compare the Bulldozer KVM results against other Intel and AMD CPUs, etc. A wide variety of open-source Linux benchmarks were run from the Phoronix Test Suite.
(If you missed it, this morning are also some new AMD Bulldozer compiler benchmarks under Linux with more being on the way. Among the other upcoming Bulldozer articles while I'm away are overclocking results, Cool 'n' Quiet / TurboCore performance results, and Open64 5.0 compiler results. There's also a shocking Bulldozer finding to be noted soon.)
If you're interested in Linux virtualization performance, other results that you may be interested in from October and November include the Ubuntu 11.10: Xen vs. KVM vs. VirtualBox, KVM x86/x86_64: Ubuntu 8.04 LTS Through Ubuntu 11.10, and VirtualBox 4.1 OpenGL 3D Guest Performance.