Hyper-V Integration Component drivers for Linux as Open Source

What!!!
This is the first time that Microsoft has contributed code to the Linux kernel.
The Hyper-V Linux device drivers will be licensed under GPLv2. That's 20,000 lines of code that provide the synthetic device drivers and VM bus implementation needed for a Linux guest OS to run "enlightened" on either Windows Server 2008 Hyper-V or Microsoft Hyper-V Server 2008.

Read more here and here.