[Intel-gfx] [PATCH] drm/i915: Retry gtt fault when out of fence register

[Ville Syrjälä]

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 at 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 at linux.intel.com>
> 
> Reviewed-by: Andi Shyti <andi.shyti at linux.intel.com> 

Thanks. Pushed to gt-next.

-- 
Ville Syrjälä
Intel