reproduce (this is a W=1 build):
        git checkout 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
        b4 shazam https://lore.kernel.org/r/1-v1-20c73f153f4c+1895-vtd_prep_jgg@nvidia.com
        # 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/