The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From b18fc0ab837381c1a6ef28386602cd888f2d9edf Mon Sep 17 00:00:00 2001 From: Pierre-Eric Pelloux-Prayer <[email protected]> Date: Mon, 9 Feb 2026 18:54:45 +0100 Subject: [PATCH] drm/amdgpu: fix sync handling in amdgpu_dma_buf_move_notify MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: [email protected] Fixes: a448cb003edc ("drm/amdgpu: implement amdgpu_gem_prime_move_notify v2") Signed-off-by: Pierre-Eric Pelloux-Prayer <[email protected]> Reviewed-by: Christian König <[email protected]> Signed-off-by: Alex Deucher <[email protected]> --- 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 b9c38a4fe546a..656c267dbe587 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c @@ -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", -- 2.51.0
