Created attachment 141174 [details] [review]
add_debug_info.patch

A am attaching a basic debug patch, please try to apply it. It should give a
bit more info in dmesg whe VM fault happens. I wasn't able to test it on  my
system so it might be buggy or crash.

Reproduce again like before with the cmd-trace like before and once the fault
happens if possible try quickly run 

sudo umr -O halt_waves -wa

and only if you still have running system after that do the 
sudo umr -O verbose -R gfx[.]

The driver should be loaded amdgpu.vm_fault_stop=2 from grub
Also check if adding amdgpu.vm_debug=1 makes the issue reproduce more quickly