Re: [PATCH v2] xen/arm, xen/common: Add Kconfig option to control Dom0 boot

[dmkhn@proton.me]

On Mon, Jul 28, 2025 at 05:07:30PM +0000, Oleksii Moisieiev wrote:
> This commit introduces a new Kconfig option, `CONFIG_DOM0_BOOT`, to
> allow for building Xen without support for booting a regular domain (Dom0).
> This functionality is primarily intended for the ARM architecture.
> 
> A new Kconfig symbol, `HAS_DOM0`, has been added and is selected by
> default for ARM and X86 architecture. This symbol signifies that an
> architecture has the capability to support a Dom0.
> 
> The `DOM0_BOOT` option depends on `HAS_DOM0` and defaults to 'y'. For
> expert users, this option can be disabled (`CONFIG_EXPERT=y` and no
> `CONFIG_DOM0_BOOT` in the config), which will compile out the Dom0
> creation code on ARM. This is useful for embedded or dom0less-only
> scenarios to reduce binary size and complexity.
> 
> The ARM boot path has been updated to panic if it detects a non-dom0less
> configuration while `CONFIG_DOM0_BOOT` is disabled, preventing an invalid
> boot.
> 
> Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@epam.com>
> 
> ---
> 
> ---
>  xen/arch/arm/Kconfig        |  1 +
>  xen/arch/arm/domain_build.c |  8 ++++++++
>  xen/arch/arm/setup.c        | 14 ++++++++++----
>  xen/arch/x86/Kconfig        |  1 +
>  xen/common/Kconfig          | 11 +++++++++++
>  5 files changed, 31 insertions(+), 4 deletions(-)

I think there should be changes in
  include/xen/domain.h
and
  arch/arm/include/asm/setup.h
to compile out declarations of dom0_max_vcpus() and create_dom0() under new
CONFIG_DOM0_BOOT.

I would also define default implementations using ASSERT_UNREACHABLE() under
#ifndef CONFIG_DOM0_BOOT.