Comment # 20 on bug 102500 from charlie

I confirm that bug 102500 and bug 102598 are the same.

I split up the patch into 3 parts and they applied cleanly with offsets to
drm-next-4.15-wip.

I then reverted mesa to commit 214b565bc28bc4419f3eec29ab7bbe34080459fe
(winsys/amdgpu: set AMDGPU_GEM_CREATE_VM_ALWAYS_VALID if possible v2) compiled
and started X and corruption and lockups are gone.