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Date:   Tue, 19 Apr 2022 12:32:25 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Eric DeVolder <eric.devolder@oracle.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, bhe@redhat.com, vgoyal@redhat.com,
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        robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com,
        konrad.wilk@oracle.com, boris.ostrovsky@oracle.com
Subject: Re: [PATCH v7 2/8] x86/crash: Introduce new options to support cpu
 and memory hotplug
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References: <20220413164237.20845-1-eric.devolder@oracle.com>
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On Mon, Apr 18, 2022 at 05:03:39PM -0500, Eric DeVolder wrote:
> I've examined the code with this thought in mind, and I'm not exactly sure how
> this code should be restructured for !HOTPLUG stubs. I'd very much appreciate
> an example in order to facilitate accommodating the request!

For example, see init_intel_microcode() in arch/x86/include/asm/microcode.h:

#ifdef CONFIG_MICROCODE_INTEL
extern struct microcode_ops * __init init_intel_microcode(void);
#else
static inline struct microcode_ops * __init init_intel_microcode(void)
{
        return NULL;
}
#endif /* CONFIG_MICROCODE_INTEL */

The actual definition then is in:

   arch/x86/kernel/cpu/microcode/intel.c:
   struct microcode_ops * __init init_intel_microcode(void)

and it gets enabled when CONFIG_MICROCODE_INTEL is enabled in the
.config. When CONFIG_MICROCODE_INTEL=n, the static inline stub gets used
and optimized away by the compiler.

HTH.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette