linux-kernel - Re: Bisected regression

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Date:	Thu, 10 Dec 2009 14:44:55 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Roland Dreier <rdreier@...co.com>,
	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>
Subject: Re: Bisected regression

On 12/10/2009 11:50 AM, Yinghai Lu wrote:
> Roland Dreier wrote:
>>  > that BIOS is using first 64k for mptable. and after booting those
>>  > mptable is overwritten by trampoline.
>>
>> So fix that BIOS people should do is to move the mptable above 64K and
>> leave low 64K empty?
> 
> Yes. should be below and near 1M, and use e820 to reserve it.
> 

Keep in mind BIOS loads and runs the OS bootloader at 0x7c00.  If this
is a conventional BIOS, there is absolutely no way such a table is
intact by the time the OS runs.

The BIOS should, indeed put it either in the UMA (0xc800..0xffff) or at
the top of DOS memory (just below 640K) and reserve it in e820.
Anything else is irreparably broken.

	-hpa

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