Windows VirtIO Drivers
The source for the Windows drivers is in a git repository on kernel.org
Binary drivers are provided by some Linux distributions including WHQL Certified drivers.
For Windows 7 and Windows Server 2008 drivers need to be signed by the packager.
In addition these platforms require WHQL certified and signed drivers.
If your distribution does not provide binary drivers the Fedora Project package can be downloaded from the following link.
Note: These drivers are signed but not WHQL Certified.