Here's a snippet from Mike's blog on Linux Integration for Hyper-V:

The final version of the Linux Integration Components for Hyper-V have been released!

Driver support for synthetic devices: The Linux integration components include support for both the synthetic network controller and synthetic storage controller that have been developed specifically for Hyper-V. These components take advantage of the new high-speed bus, VMBus, which was developed for Hyper-V.
Hypercall adapter: The Hypercall adapter is a thin layer of software that translates the Xen-specific virtualization function calls from a Xen-enabled Linux kernel to Microsoft Hyper-V hypercalls. This results in improved performance for the Linux virtual machine.
Fastpath Boot Support: Boot devices now take advantage of the storage VSC to provide enhanced performance.
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Read the full posting at source here

Read the complete post at http://wmug.co.uk/blogs/r0b/archive/2008/09/10/hyper-v-linux-integration-components.aspx