reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/commit/?id=4a9f36010eba44853b3c9bb721a4a5f4319dc370
        git remote add rppt https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git
        git fetch --no-tags rppt kho/v4
        git checkout 4a9f36010eba44853b3c9bb721a4a5f4319dc370
        # 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 kernel/ mm/