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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

~Andrew