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

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,
	tglx@linutronix.de, mingo@redhat.com,
	dave.hansen@linux.intel.com, hpa@zytor.com,
	nramas@linux.microsoft.com, thomas.lendacky@amd.com,
	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
Date: Tue, 19 Apr 2022 12:32:25 +0200	[thread overview]
Message-ID: <Yl6PueNCZZeobMWr@zn.tnic> (raw)
In-Reply-To: <f3ea7ee0-1cb8-6928-d0af-4c2fc63a42a4@oracle.com>

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