reproduce (this is a W=1 build):
        # https://github.com/yiliu1765/iommufd/commit/409be2dd13f01025d30d24b78287beaf85a02eed
        git remote add yiliu1765-iommufd https://github.com/yiliu1765/iommufd.git
        git fetch --no-tags yiliu1765-iommufd wip/iommu_cache_flush_refactor
        git checkout 409be2dd13f01025d30d24b78287beaf85a02eed
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash drivers/iommu/intel/