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

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Date:	Wed, 7 Aug 2013 23:34:01 +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: Yu, Fenghua
> Sent: Wednesday, August 07, 2013 3:46 PM
> 
> > 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.
> 

Maybe need to change the check as follows to take care of CPU0 hot add case?

if ((cpu && system_state == SYSTEM_BOOTING) || (system_state == SYSTEM_RUNNING))
	load_ucode_ap();

Thanks.

-Fenghua