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drm/amdgpu: fix sync handling in amdgpu_dma_buf_move_notify

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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: a448cb003e ("drm/amdgpu: implement amdgpu_gem_prime_move_notify v2")
Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Pierre-Eric Pelloux-Prayer 2026-02-09 18:54:45 +01:00 committed by Alex Deucher
parent 9aca641143
commit b18fc0ab83
1 changed files with 8 additions and 1 deletions
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9
drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
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@ -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",