linux-kernel - Re: Bisected regression (Was Re: current -git fails to boot on nehalem-ex)

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Message-ID: <4B217C0E.9040801@zytor.com>
Date:	Thu, 10 Dec 2009 14:54:06 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Jens Axboe <jens.axboe@...cle.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Randy Dunlap <randy.dunlap@...cle.com>
Subject: Re: Bisected regression (Was Re: current -git fails to boot on	nehalem-ex)

On 12/10/2009 02:45 PM, Yinghai Lu wrote:
> H. Peter Anvin wrote:
>> On 12/10/2009 01:07 PM, Yinghai Lu wrote:
>>> it turns out BIOS is using first 64k for mptable without reserve it.
>>>
>>> so try to find good range for it instead of hard code it.
>>> in case some bios try to use that range for sth.
>>>
>>
>> Is this an EFI BIOS?  Otherwise, the first 64K would be clobbered anyway
>> by the boot loader, so it is invalid anyway...  If it is EFI, it is
>> theoretically possible.
> 
> Jens said acpi=off works with 2.6.32.
> 
> can you specify the exact byte position that boot loader could touched?
> 

A legacy-BIOS boot loader will typically clobber all memory from 0x600
(in theory 0x501) up to the FBM point; a pointer to the FBM mark is
given by (*(uint16_t *)0x413) << 10.

	-hpa

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