i have been having somewhat unreproduceable lockups with my rx 56 vega all
going from 4.12 amd-staging up until 4.15-rc2 where its mainlined. but for some
reason i can reproduce it now with simply just open pavucontrol, and weirdly
enough only that.

i can properly play games, dirt rally, cs:go, run benchmarks or just leave the
computer on for days. but as fast as i open pavucontrol it lockups and this
happends in dmesg. and i dont seem to be all alone with it either, here is a
user with a rx 64 vega on archlinux having same issue/errors. 
https://bbs.archlinux.org/viewtopic.php?id=232519


amdgpu 0000:03:00.0: VM_L2_PROTECTION_FAULT_STATUS:0x00000000
amdgpu 0000:03:00.0:   at page 0x0000000000000000 from 27
amdgpu 0000:03:00.0: [gfxhub] VMC page fault (src_id:0 ring:171 vm_id:4
pas_id:0)

System info:
Radeon RX Vega (VEGA10 / DRM 3.23.0 / 4.15.0-rc2-mainline, LLVM 6.0.0)
Mesa 17.4.0-devel (git-4c7af87fb9)