https://bugs.freedesktop.org/show_bug.cgi?id=58667
--- Comment #5 from Thomas Rohloff v10lator@myway.de --- I should really read before I click save, sorry. Here again:
"Is this a regression? Does it happen with older versions of mesa or kernel?" Not that I know about.
"May also be related to bug 58354." Do you have a link to the patch noted there ("drm/radeon: use DMA engine for VM page table updates on cayman/TN") ? I would love to try to revert this patch and test it, but I'm unable to google it.