Last week's Phoronix article provides an overview of this experimental project by Red Hat's David Airlie to open up 3D support to QEMU guests using VirtIO. The guest has a DRM and DDX driver along with a Gallium3D component while the host system doesn't need to be Mesa/Gallium3D based but simply have a working OpenGL driver and GPU.
For those interested in more technical details on the Virgil3D project, David Airlie has now published an architecture and design document concerning this project. "This document describes the architecture of the virgil3d virtual GPU for providing 3D capabilities to qemu guest operating systems. This document is written from the point of view of running a modern Linux guest graphics stack."