[PATCH 1/1] drm/i915: Drop user contexts on device remove

[Janusz Krzysztofik]

Hi Chris,

On Fri, 2020-04-24 at 15:15 +0100, Chris Wilson wrote:
> Quoting Chris Wilson (2020-04-24 15:09:27)
> > Quoting Janusz Krzysztofik (2020-04-24 14:47:42)
> > > Contexts associated with open file descriptors are now closed on file
> > > close.  If a device is removed while being open, DMA API warns about
> > > device associated mappings still active.  Moreover, subsequent removal
> > > of contexts on device close may trigger a bug in intel-iommu code on
> > > dma_unmap attempt.
> > 
> > The contexts are not the primary association with dma-mappings. The
> > objects are dma-mapped independently, what you are doing here is
> > indirectly releasing the dma-mapping of the ppGTT page directory.
> > 
> > While it seems to be only solving half the problem, automatically
> > marking the vm as closed on driver_unregister sounds viable. But it
> > feels like we should just be marking the device as going away and just
> > ignore all the dma unmapping.
> > 
> > We could do something like set up a dummy dma_map_ops in unregister,
> > and so discard all the unmaps, report error for further maps, and leave
> > in place until the next device replaces it. It appears that can be done
> > with just a blank dma_map_ops. Seems cheeky, but it just might work...
> 
> I wonder if
> 
> void i915_driver_remove(struct drm_i915_private *i915)
> 
>         i915_driver_hw_remove(i915);
> 
> +       set_dma_ops(&i915->drm.pdev->dev, &dma_dummy_ops);
> +
>         enable_rpm_wakeref_asserts(&i915->runtime_pm);
>  }
> 
> is all we need.

Thanks for sharing that idea.  I can try to implement it if you haven't
started yet.

Thanks,
Janusz

> -Chris