CVE-2026-43318: drm/amdgpu: fix sync handling in amdgpu_dma_buf_move_notify

In the Linux kernel, the following vulnerability has been resolved:

drm/amdgpu: fix sync handling in amdgpudmabufmovenotify

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 amdgpuvmhandlemoved 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: drmschedjobrun # GPU0, frame rendering drmschedjobqueue # GPU0, blit drmschedjobdone # GPU0, frame rendering drmschedjobrun # GPU0, blit move linear buffer for GPU1 access # amdgpudmabufmovenotify -> update pt # GPU0

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