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

[Chris Wilson]

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.
-Chris