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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 22 Nov 2023 13:08:41 -0800
Message-ID: <CAHk-=wh03jMZRAxHFTkv0h9dZ6TmiqukzcHd4RTx7ijia_prsg@mail.gmail.com>
Subject: Re: [regression] microcode files missing in initramfs imgages from
 dracut (was Re: [PATCH] x86: Clean up remaining references to CONFIG_MICROCODE_AMD)
To:     Borislav Petkov <bp@alien8.de>
Cc:     Linux regressions mailing list <regressions@lists.linux.dev>,
        lukas.bulwahn@gmail.com, dave.hansen@linux.intel.com,
        hpa@zytor.com, kernel-janitors@vger.kernel.org,
        linux-kernel@vger.kernel.org, mingo@redhat.com, tglx@linutronix.de,
        x86@kernel.org
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On Wed, 22 Nov 2023 at 12:51, Borislav Petkov <bp@alien8.de> wrote:
>
> My only worry here is that we're making a precedent and basically saying
> that it is ok for tools to grep .config to figure out what is supported
> by the kernel. And then other tools might follow.

Yes, I agree that it's not optimal, but I would hate to have some odd
"let's add another ELF note" churn too, for (presumably) increasingly
obscure reasons.

It looks like dracut has been doing this forever, and in fact back in
2015 apparently had the exact same issue (that never made it to kernel
developers, or at least not to me), when the kernel
CONFIG_MICROCODE_xyz_EARLY config went away, and became just
CONFIG_MICROCODE_xyz.

The whole "check kernel config" in dracut seems to go back to 2014, so
it's been that way for almost a decade by now.

Honestly, I think the right approach may be to just remove the check
again from dracut entirely - the intent seems to be to make the initrd
smaller when people don't support microcode updates, but does that
ever actually *happen*?

There are dracut command lines, like "--early-microcode" and
"--no-early-microcode", so people who really want to save space could
just force it that way. Doing the CONFIG_xyz check seems broken.

But that's for the dracut people to worry about.

I guess we on the kernel side could help with "make install" etc, but
we've (intentionally) tried to insulate us from distros having
distro-specific installkernel scripts, so we don't really haev a good
way to pass information down to the installkernel side.

It *would* make sense if we just had some actual arguments we might
pass down. Right now we just do

        exec "${file}" "${KERNELRELEASE}" "${KBUILD_IMAGE}" System.map
"${INSTALL_PATH}"

so basically the only argument we pass down is that INSTALL_PATH
(which is just "/boot" by default).

            Linus