(In reply to comment #5)
> 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.

"Is this a regression?  Does it happen with older versions of mesa or kernel?"
Yes. Previous kernel 3.7 doesn't show this problem.