Re: [PATCH 0/4] Add Kconfig option to remove microcode loading support

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.11.2025 09:50, Andrew Cooper wrote:
> On 12/11/2025 4:22 pm, Alejandro Vallejo wrote:
>>  xen/arch/x86/Kconfig                    | 12 ++++
>>  xen/arch/x86/cpu/microcode/Makefile     |  9 ++-
>>  xen/arch/x86/cpu/microcode/amd-base.c   | 55 +++++++++++++++++++
>>  xen/arch/x86/cpu/microcode/amd.c        | 55 ++-----------------
>>  xen/arch/x86/cpu/microcode/amd.h        | 15 +++++
>>  xen/arch/x86/cpu/microcode/base.c       | 73 +++++++++++++++++++++++++
>>  xen/arch/x86/cpu/microcode/core.c       | 58 +-------------------
>>  xen/arch/x86/cpu/microcode/intel-base.c | 50 +++++++++++++++++
>>  xen/arch/x86/cpu/microcode/intel.c      | 56 +++----------------
>>  xen/arch/x86/cpu/microcode/intel.h      | 16 ++++++
>>  xen/arch/x86/cpu/microcode/private.h    | 14 +++++
>>  xen/arch/x86/efi/efi-boot.h             |  2 +-
>>  xen/arch/x86/platform_hypercall.c       |  2 +
>>  13 files changed, 259 insertions(+), 158 deletions(-)
>>  create mode 100644 xen/arch/x86/cpu/microcode/amd-base.c
>>  create mode 100644 xen/arch/x86/cpu/microcode/amd.h
>>  create mode 100644 xen/arch/x86/cpu/microcode/base.c
>>  create mode 100644 xen/arch/x86/cpu/microcode/intel-base.c
>>  create mode 100644 xen/arch/x86/cpu/microcode/intel.h
> 
> This is awfully invasive for something that ultimately drops only a
> handful of lines of code.
> 
> First, it should be CONFIG_MICROCODE_LOADING.  We're not getting rid of
> all microcode capabilities.  Also, of all the places where UCODE needs
> expanding properly, it's Kconfig.
> 
> Next, annotate the functions that you conditionally don't reference in
> {amd,intel}_ucode_ops with __maybe_unused, and dead code elimination
> should do the rest.

Are you, btw, sure this would be Misra-compliant? Right now we solely
deviate __maybe_unused when used on labels which may really be unused,
afaics.

Jan