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

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Message-ID: <3E5A0FA7E9CA944F9D5414FEC6C712205A53B6E9@ORSMSX106.amr.corp.intel.com>
Date:	Wed, 7 Aug 2013 22:46:13 +0000
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	Borislav Petkov <bp@...en8.de>,
	Torsten Kaiser <just.for.lkml@...glemail.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.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: Wednesday, July 24, 2013 6:33 AM
> On Tue, Jul 23, 2013 at 11:00:26PM +0200, Torsten Kaiser wrote:
> > Extract common checks and initialisations from load_ucode_ap() and
> > save_microcode_in_initrd_amd() to load_microcode_amd_early().
> > load_ucode_ap() gets a quick exit for !cpu, because for the BSP there
> is
> > already a different function dealing with its update.
> >
> > The original code already didn't anything, because without
> load_microcode_amd()
> > getting called apply_microcode_amd() could not do anything.
> >
> > Signed-off-by: Torsten Kaiser <just.for.lkml@...glemail.com>
> >
> > --- a/arch/x86/kernel/microcode_amd_early.c	2013-07-22
> 06:22:32.000000000 +0200
> > +++ b/arch/x86/kernel/microcode_amd_early.c	2013-07-23
> 20:00:04.889508712 +0200
> > @@ -196,6 +196,23 @@ void __init load_ucode_amd_bsp(void)
> >  	apply_ucode_in_initrd(cd.data, cd.size);
> >  }
> >
> > +static int load_microcode_amd_early(void)
> > +{
> > +	enum ucode_state ret;
> > +	void *ucode;
> > +
> > +	if (ucode_loaded || !ucode_size || !initrd_start)
> > +		return 0;
> > +
> > +	ucode = (void *)(initrd_start + ucode_offset);
> > +	ret = load_microcode_amd(0, ucode, ucode_size);
> > +	if (ret != UCODE_OK)
> > +		return -EINVAL;
> > +
> > +	ucode_loaded = true;
> > +	return 0;
> > +}
> > +
> >  #ifdef CONFIG_X86_32
> >  u8 amd_bsp_mpb[MPB_MAX_SIZE];
> >
> > @@ -258,17 +275,13 @@ void load_ucode_amd_ap(void)
> >
> >  	collect_cpu_info_amd_early(&cpu_data(cpu), ucode_cpu_info + cpu);
> >
> > -	if (cpu && !ucode_loaded) {
> > -		void *ucode;
> > -
> > -		if (!ucode_size || !initrd_start)
> > -			return;
> > +	/* BSP via load_ucode_amd_bsp() */
> > +	if (!cpu)
> > +		return;
> 
> Ok, this is really misleading. Fenghua, what's the reason for calling
> load_ucode_ap() on the BSP too?
> 
> We have on the one hand:
> 
> x86_64_start_kernel
> |->load_ucode_bsp
> 
> and on the other:
> 
> x86_64_start_kernel
> |-> x86_64_start_reservations
>     |-> start_kernel
>         |-> trap_init
> 	    |-> cpu_init
> 	        |-> load_ucode_ap()
> 
> so we attempt to load the ucode twice on the BSP.
> 

You are right. Though the second time loading attempt will not find a valid/newer ucode patch to update. So this won't cause a real/serious problem. But we had better to fix this anyway.

> IMO, we should do this in cpu_init:
> 
> 	if (cpu)
> 		load_ucode_ap();
> 
> no?

This check won't work when CPU0 is hot added. So we need to find a better way to fix this.

Thanks.

-Fenghua