Guys have you actually looked at the following line ?
Aperture size is 268435456 MiB -- That is 256 TiB !!!

That's rather impossible amount if you ask me. So there's either a bug in IGT's
gem_aperture_size() or one of the two ioctls (I915_GEM_CONTEXT_GETPARAM
I915_GEM_GET_APERTURE) that it uses.

With a couple of print statements you should be able to quickly track the exact
offender. Good luck !