AMDGPU_VA_RESERVED_TOP
vm_size -= AMDGPU_VA_RESERVED_TOP;
vm_size -= AMDGPU_VA_RESERVED_TOP;
(AMDGPU_VA_RESERVED_TOP >> AMDGPU_GPU_PAGE_SHIFT);
(AMDGPU_VA_RESERVED_TOP >> AMDGPU_GPU_PAGE_SHIFT);
(AMDGPU_VA_RESERVED_TOP >> AMDGPU_GPU_PAGE_SHIFT);