On Fri, Oct 13, 2023 at 12:53:59PM +0200, Andi Shyti wrote:
Hi Ville,
If we can't find a free fence register to handle a fault in the GMADR range just return VM_FAULT_NOPAGE without populating the PTE so that userspace will retry the access and trigger another fault. Eventually we should find a free fence and the fault will get properly handled.
A further improvement idea might be to reserve a fence (or one per CPU?) for the express purpose of handling faults without having to retry. But that would require some additional work.
Looks like this may have gotten broken originally by commit 39965b376601 ("drm/i915: don't trash the gtt when running out of fences") as that changed the errno to -EDEADLK which wasn't handle by the gtt fault code either. But later in commit 2feeb52859fc ("drm/i915/gt: Fix -EDEADLK handling regression") I changed it again to -ENOBUFS as -EDEADLK was now getting used for the ww mutex dance. So this fix only makes sense after that last commit.
Cc: stable@vger.kernel.org Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/9479 Fixes: 2feeb52859fc ("drm/i915/gt: Fix -EDEADLK handling regression") Signed-off-by: Ville Syrjälä ville.syrjala@linux.intel.com
Reviewed-by: Andi Shyti andi.shyti@linux.intel.com
Thanks. Pushed to gt-next.