Commit b18fc0ab authored by Pierre-Eric Pelloux-Prayer's avatar Pierre-Eric Pelloux-Prayer Committed by Alex Deucher
Browse files

drm/amdgpu: fix sync handling in amdgpu_dma_buf_move_notify 



Invalidating a dmabuf will impact other users of the shared BO.
In the scenario where process A moves the BO, it needs to inform
process B about the move and process B will need to update its
page table.

The commit fixes a synchronisation bug caused by the use of the
ticket: it made amdgpu_vm_handle_moved behave as if updating
the page table immediately was correct but in this case it's not.

An example is the following scenario, with 2 GPUs and glxgears
running on GPU0 and Xorg running on GPU1, on a system where P2P
PCI isn't supported:

glxgears:
  export linear buffer from GPU0 and import using GPU1
  submit frame rendering to GPU0
  submit tiled->linear blit
Xorg:
  copy of linear buffer

The sequence of jobs would be:
  drm_sched_job_run                       # GPU0, frame rendering
  drm_sched_job_queue                     # GPU0, blit
  drm_sched_job_done                      # GPU0, frame rendering
  drm_sched_job_run                       # GPU0, blit
  move linear buffer for GPU1 access      #
  amdgpu_dma_buf_move_notify -> update pt # GPU0

It this point the blit job on GPU0 is still running and would
likely produce a page fault.

Cc: stable@vger.kernel.org
Fixes: a448cb00 ("drm/amdgpu: implement amdgpu_gem_prime_move_notify v2")
Signed-off-by: default avatarPierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: default avatarChristian König <christian.koenig@amd.com>
Signed-off-by: default avatarAlex Deucher <alexander.deucher@amd.com>
parent 9aca6411

drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c

+8 −1
Original line number Diff line number Diff line
@@ -514,8 +514,15 @@ amdgpu_dma_buf_move_notify(struct dma_buf_attachment *attach) 
		r = dma_resv_reserve_fences(resv, 2);

		if (!r)

			r = amdgpu_vm_clear_freed(adev, vm, NULL);



		/* Don't pass 'ticket' to amdgpu_vm_handle_moved: we want the clear=true

		 * path to be used otherwise we might update the PT of another process

		 * while it's using the BO.

		 * With clear=true, amdgpu_vm_bo_update will sync to command submission

		 * from the same VM.

		 */

		if (!r)

			r = amdgpu_vm_handle_moved(adev, vm, ticket);

			r = amdgpu_vm_handle_moved(adev, vm, NULL);



		if (r && r != -EBUSY)

			DRM_ERROR("Failed to invalidate VM page tables (%d))\n",