CVE-2026-43370 drm/amdgpu: Fix use-after-free race in VM acquire

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: Fix use-after-free race in VM acquire Replace non-atomic vm-processinfo assignment with cmpxchg to prevent race when parent/child processes sharing a drmfile both try to acquire the same VM after fork. cherry picked...