reproduce (this is a W=1 build):
        # https://github.com/jgunthorpe/linux/commit/2edad14f2cea09830a4fbaf4352834f474ce4394
        git remote add jgunthorpe https://github.com/jgunthorpe/linux
        git fetch --no-tags jgunthorpe iommufd_dmabuf
        git checkout 2edad14f2cea09830a4fbaf4352834f474ce4394
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash