The main function is to check whether the corresponding IOMMU buffer is unmapped when dmabuf is released, so as to avoid memory coverage caused by IOMMU. Bug: 438090847 Change-Id: I56ae3f0994cd4f3d24494b7972e4d89d0f004da8 Signed-off-by: Gaofeng Sheng <gaofeng.sheng@unisoc.com> (cherry picked from commit 8879650556ed747baf5a4d3037d687a76ccb986f)