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Date:	Thu, 20 Dec 2012 08:48:31 -0800
From:	"H. Peter Anvin" <>
To:	Yinghai Lu <>
CC:	"Zhang, Lin-Bao (Linux Kernel R&D)" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>
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)
> <> 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.


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