linux-kernel - Re: [regression] 3.7 ends in APIC panic

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Date:	Mon, 17 Dec 2012 14:11:06 +0100
From:	Bernd Schubert <bernd.schubert@...m.fraunhofer.de>
To:	Borislav Petkov <bp@...en8.de>, Yinghai Lu <yinghai@...nel.org>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Weidong Han <weidong.han@...el.com>,
	David Woodhouse <David.Woodhouse@...el.com>, sbsiddha@...il.com
Subject: Re: [regression] 3.7 ends in APIC panic

On 12/17/2012 11:00 AM, Borislav Petkov wrote:
> + 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:
>>> https://lwn.net/Articles/289881/
>>>
>>>> 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
> case.
>
>> 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
> http://marc.info/?l=linux-kernel&m=135540103415652 then?

Oh huh, that is the dmesg from 3.4.7, which booted fine. I just sent it 
hoping it would help to see where the issue comes from.
When I run "make oldconfig" for 3.7.0 I accidentally unset 
CONFIG_IRQ_REMAP, wich also unset CONFIG_X86_X2APIC :(

>
> 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?

No need, as I said above, the printk comes from a different kernel with 
a different config. With either CONFIG_IRQ_REMAP=false or 
CONFIG_X86_X2APIC=false the booting ends in a kernel panic.

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

No, only partly with "noapic", but that makes ahci to fail to detect 
disks later on.

>
>> 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.
>
> Thanks.
>


Cheers,
Bernd
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