On Mon, Dec 19, 2016 at 12:39:16PM +0100, Juergen Gross wrote:
With recent 4.10 kernel the graphics isn't coming up under Xen. First failure message is:
[ 46.656649] i915 0000:00:02.0: swiotlb buffer is full (sz: 1630208 bytes)
Do we get a silent failure? i915_gem_gtt_prepare_pages() is where we call dma_map_sg() and pass the sg to swiotlb (in this case) for remapping, and we do check for an error value of 0. After that error, SWIOTLB_MAP_ERROR is propagated back and converted to 0 for dma_map_sg(). That looks valid, and we should report ENOMEM back to the caller.
Later I see splats like:
[ 49.393583] general protection fault: 0000 [#1] SMP
What was the faulting address? RAX is particularly non-pointer-like so I wonder if we walked onto an uninitialised portion of the sgtable. We may have tripped over a bug in our sg_page iterator.
The attached patch should prevent an early ENOMEM following the swiotlb allocation failure. But I suspect that we will still be tripping up the failure in the sg walker when binding to the GPU. -Chris