linux-kernel - RE: [PATCH 3/5] x86, AMD: cleanup: merge common code in early microcode loading

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Date:	Fri, 9 Aug 2013 18:44:41 +0000
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>
CC:	Torsten Kaiser <just.for.lkml@...glemail.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Jacob Shin <jacob.shin@....com>,
	Johannes Hirte <johannes.hirte@....tu-ilmenau.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 3/5] x86, AMD: cleanup: merge common code in early
 microcode loading

> From: Borislav Petkov [mailto:bp@...en8.de]
> Sent: Thursday, August 08, 2013 11:29 AM

> On Thu, Aug 08, 2013 at 12:02:38PM +0200, Borislav Petkov wrote:
> > On Wed, Aug 07, 2013 at 07:22:39PM -0700, H. Peter Anvin wrote:
> > > How much does this matter?
> >
> > I know what you're asking :-)
> >
> > And no, it doesn't really matter as we fail in the patch version
> check
> > so maybe only a comment will suffice here so that people don't get
> > confused.
> 
> IOW, something like that:
> 
> ---
> From: Borislav Petkov <bp@...e.de>
> Date: Thu, 8 Aug 2013 20:26:24 +0200
> Subject: [PATCH] x86, microcode: Clarify loading on the AP
> 
> Hold it down why we're calling the AP microcode loading routine on the
> BSP too, for future reference.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> ---
>  arch/x86/kernel/cpu/common.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/common.c
> b/arch/x86/kernel/cpu/common.c
> index 25eb2747b063..58d37a27d317 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1226,8 +1226,12 @@ void cpu_init(void)
>  	int i;
> 
>  	/*
> -	 * Load microcode on this cpu if a valid microcode is available.
> -	 * This is early microcode loading procedure.
> +	 * Load microcode on this cpu if a valid microcode is available.
> This
> +	 * is early microcode loading procedure. We execute this on the
> BSP too
> +	 * but since a microcode has been potentially already applied on
> the
> +	 * BSP, we will return prematurely here. It is easier to simply
> call it
> +	 * again than filtering all the possible cases when we're not
> running
> +	 * on the BSP.
>  	 */
>  	load_ucode_ap();

Load_ucode_ap() running on BSP during boot time wastes short time on scanning ucode blob. But the time should be very short. 

Reviewed-by: Fenghua Yu <fenghua.yu@...el.com>