Re: [PATCH 0/3] x86: Make processor vendor selection available without EXPERT

[Vincent Mailhol]

On 31/10/2026 at 22:43, Borislav Petkov wrote:
> On Sat, Oct 31, 2026 at 08:51:48AM +0100, Vincent Mailhol wrote:
>> Restricting a kernel build to a known CPU vendor currently requires
>> enabling EXPERT.
>>
>> Make PROCESSOR_SELECT available without EXPERT. It remains disabled by
>> default, preserving support for all applicable CPU vendors in existing
>> configurations.
> 
> What I am not seeing is git archeology about why it is behind EXPERT and
> whether that reason is or is not valid anymore.

PROCESSOR_SELECT was introduced in 2008 by commit 8d02c2110b3f ("x86:
configuration options to compile out x86 CPU support code"). At that
time, it was gated by CONFIG_EMBEDDED with space savings given as the
main motivation. In the thread [1], Bodo pointed out that this wasn't
specific to embedded systems but his comment didn't get any replies.

Commit 6a108a14fa35 ("kconfig: rename CONFIG_EMBEDDED to
CONFIG_EXPERT") then did a treewide renaming. The commit explains that
EMBEDDED already covered nonstandard configurations beyond embedded
systems but does not give a PROCESSOR_SELECT-specific rationale.

Beyond Bodo's unanswered comment, I did not find further discussion of
the relevance of PROCESSOR_SELECT for non-embedded machines or the
Kconfig user experience. The main point I am raising in this series is
how easily users should be able to disable all the features specific
to CPU vendors they do not need. I think this aspect deserves further
discussion.

Finally, the size savings have changed since 2008. As reported in my
tests, an AMD-only build reduces vmlinux.o size by 8.88%. What used to
be a micro-optimization back then now has a much bigger impact.

[1] https://lore.kernel.org/all/E1KRp7q-0001pd-61@xxxxxxxxxxxxxxxxxxxxxx/


Yours sincerely,
Vincent Mailhol