linux-kernel - Re: [PATCH v7 2/8] x86/crash: Introduce new options to support cpu and memory hotplug

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Message-ID: <Yl6PueNCZZeobMWr@zn.tnic>
Date:   Tue, 19 Apr 2022 12:32:25 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Eric DeVolder <eric.devolder@...cle.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com
Subject: Re: [PATCH v7 2/8] x86/crash: Introduce new options to support cpu
 and memory hotplug

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