It is slightly different - this runs an unmodified GPU driver in the guest (no para-virtualization) and in our observations our performance is close to native which I believe is a fair improvement over the overhead of Virgl. Also there's availability of more APIs - for example DirectX, Vulkan, and OpenGL work with GVM guests. I don't think all of those work with Virgl. We make use of various different assistance modes (either hardware or software I/O virtualization/resource sharing) via VFIO-Mdev (VFIO Mediated Device), or via SR-IOV (Single Root IO Virtualization), or SIOV (Scalable IO Virtualization).

I made this web page to try consolidate some information from various folks who have contributed a lot in this area of open source to show how it works (there are some novel additions we've made as well based on our own work with GVM):

https://openmdev.io/index.php/Virtual_IO_Internals