Why we didn't use embedded gem object for virtio gpu when making ttm bo a gem bo subclass?

[lepton]

Hi Gerd,

We found a bug in 5.4 kernel and virtgpu_gem_prime_mmap doesn't work
because it references vma_node in gem_base object while ttm code
initialized vma_node in tbo.base object. I am wondering, in your
original serial:
https://patchwork.kernel.org/project/dri-devel/cover/20190805124310.3275-1-kraxel@redhat.com/
(drm/ttm: make ttm bo a gem bo subclass), why you changed to use
embedded gem object for most gpu drivers but skipping virtio gpu? Is
there some specific reason?

I am thinking about CL like this (http://crrev.com/c/3092457) to fix
it and not sure if I missed something.

Thanks for your help!