reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git/commit/?id=65e07bcb16cff0067142e89cc75fb4106b102695
        git remote add kas https://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git
        git fetch --no-tags kas collapse/rfc-v1
        git checkout 65e07bcb16cff0067142e89cc75fb4106b102695

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash mm/