Linux kernel 2.6.23 introduces vSMP for KVM and Xen support

Linus Torvalds just announced availability of new Linux kernel 2.6.23.

It brings several improvements in the hardware virtualization space with the introduction of Xen and lguest support.

Kernel Newbies provides a good summary:

Lguest host support (CONFIG_LGUEST)can be compiled as a module (lg.ko). This is the host support – one you load it, your kernel will be able to run virtualized lguest guests. But kernel guests need to compile lguest guest support in order to be able to run under the lguest host. The configuration variable that enables the guest support is CONFIG_LGUEST_GUEST – but that option will be enabled automatically once you set CONFIG_LGUEST to ‘y’ or ‘m’. This means that a kernel compiled with lguest host support does also get lguest guest support. In other words, you can use the same kernel you use to be a host as guest kernel. In order to load and run new guests, you need a loader userspace program.

Part of Xen has been merged. The support included in 2.6.23 will allow the kernel to boot in a paravirtualized environment under the Xen hypervisor. But support for the hypervisor is not included – this is only guest support, no dom0, no suspend/resume, no ballooning. It’s based in the paravirt_ops infrastructure.

Anyway the most important news is support for virtual SMP inside KVM guest operating systems:

  • Enable guest smp
  • Implement rdmsr and wrmsr. This allows smp Windows to boot
  • i386: Allow KVM on i386 nonpae

More improvements are expected also in the OS virtualization space: at LinuxWorld 2007 Andrew Morton said kernel development will focus much on these technologies during the next 2 years.