reproduce (this is a W=1 build):
        # https://github.com/avpatel/linux/commit/e3141898f38de6d63cb78f33d1b1e7bfb00d6e29
        git remote add avpatel https://github.com/avpatel/linux.git
        git fetch --no-tags avpatel riscv_iommu_irqbypass_v2
        git checkout e3141898f38de6d63cb78f33d1b1e7bfb00d6e29

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um olddefconfig
        make W=1 O=build_dir ARCH=um SHELL=/bin/bash drivers/iommu/riscv/