[PATCH 6.18 704/752] drm/amdgpu: fix sync handling in amdgpu_dma_buf_move_notify

Sasha Levin
2026-02-28T17:58:38Z

From: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>

[ Upstream commit b18fc0ab837381c1a6ef28386602cd888f2d9edf ]

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: a448cb003edc ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
index ed3bef1edfe44..f20d4bc58904d 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
@@ -489,8 +489,15 @@ 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",
--
2.51.0