linux-kernel - Re: Why Linux kernel forced to enter X2APIC mode( just because of booting cpu has supported x2apic) without depending on BIOS' setting in MSR->x2apic enablement bit ?

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Message-ID: <50D3415F.8010205@zytor.com>
Date:	Thu, 20 Dec 2012 08:48:31 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	"Zhang, Lin-Bao (Linux Kernel R&D)" <linbao.zhang@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"jarkko.sakkinen@...el.com" <jarkko.sakkinen@...el.com>,
	"joerg.roedel@....com" <joerg.roedel@....com>,
	"agordeev@...hat.com" <agordeev@...hat.com>
Subject: Re: Why Linux kernel forced to enter X2APIC mode( just because of
 booting cpu has supported x2apic) without depending on BIOS' setting in MSR->x2apic
 enablement bit ?

On 12/20/2012 08:46 AM, Yinghai Lu wrote:
> On Thu, Dec 20, 2012 at 2:38 AM, Zhang, Lin-Bao (Linux Kernel R&D)
> <linbao.zhang@...com> wrote:
>> I think current core argument is our BIOS did following judgement ,
>> but Linux kernel did not(Linux seems just judge BSP supports x2apic mode or not by CPUID method)
> 
> kernel checks that, if the BSP in x2apic mode, kernel will check if
> intr-remapping can be enabled, otherwise
> it will switch back to xapic mode.
> 
>> Our BSP really supports x2apic mode, however,as this spec, our BIOS think some of configuration of server
>> could not meet x2apic conditions ,So didn't place local xAPICs into x2apic mode.
>> But linux kernel indeed enable x2apic mode(just believe BSP, didn't do above judgement) . so this is the conflict.
> 
> so your BIOS is wrong,  it does not enable intr-remapping.
> 

FWIW, I bought a *server* today and it didn't have interrupt remapping
and x2APIC, I would consider it defective and return it.

	-hpa


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