Re: [regression] 3.7 ends in APIC panic

From: Borislav Petkov
Date: Mon Dec 17 2012 - 05:00:08 EST

+ Suresh.

On Mon, Dec 17, 2012 at 10:34:46AM +0100, Bernd Schubert wrote:
> On 12/16/2012 09:39 PM, Borislav Petkov wrote:
> >On Sun, Dec 16, 2012 at 08:46:06PM +0100, Bernd Schubert wrote:
> >>Hmm, I read it the other way around - x2apic depends on interrupt
> >>remapping, but interrupt remapping can be used without x2apic.
> >
> >Ok, you're right. X2APIC should depend on IRQ_REMAP:
> >
> >
> >>The help text of CONFIG_IRQ_REMAP also says "x2APIC enhancements or to
> >>support platforms with CPU's having > 8 bit APIC ID, say Y." I guess
> >>may CPU has the latter?
> >
> >I think it is what Yinghai said - you obviously need x2apic kernel
> >support if you have IRQ_REMAP on.
> >
> >>Can the kernel panic a bit improved to help user to understand what
> >>needs to be enabled?
> >
> >Well, your kernel enables IRQ_REMAP properly:
> >
> >[ 0.031115] Enabled IRQ remapping in x2apic mode
> >
> >I guess at that stage we could probably check for x2apic support and
> >scream loudly if it is not present... IMHO.
> >
> Hmm, I think that would the wrong place,

It has to be the right place because this "Enabled IRQ..." printk above
is from the IRQ remapping code which detects an x2apic mode in your

> as the initial 3.7.0 configuration didn't have IRQ_REMAP enabled.

Huh, so why do I see the above message in your dmesg output in then?

Ok, let's sort things out here. Your .config has

# CONFIG_IRQ_REMAP is not set

but in the original dmesg you sent, the printk above comes from
intel_irq_remapping.c which gets enabled by CONFIG_IRQ_REMAP.

So, can you try enabling only CONFIG_IRQ_REMAP and leave
CONFIG_X86_X2APIC off to confirm the original observation?

Also, I'd guess your machine can boot with both options off?

> And that was the reason why x2apic got disabled during the "make
> oldconfig" process...
> Is this message an indication for missing x2apic?
> "smpboot: weird, boot (#255) not listed by the BIOS"

It's an indication that something is fishy with the apic IDs.



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