Ok, the vm faults I see are caused by using Padoka ppa which currently has https://cgit.freedesktop.org/mesa/mesa/commit/?id=847d0a393d7f0f967f39302900d5330f32b804c8 but not https://reviews.llvm.org/D41663 That means it can't be the same as the original issue, and also that the solution for me is just to update to more recent versions. Sorry for the noise in this bug.