linux-kernel - Re: [PATCH] x86: fix system die when load with "reservetop" parameter

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Date:	Mon, 24 Aug 2009 09:21:12 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Yinghai Lu <yinghai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org
Subject: Re: [PATCH] x86: fix system die when load with "reservetop"	parameter



Ingo Molnar wrote:
> * Xiao Guangrong <xiaoguangrong@...fujitsu.com> wrote:
> 
>> The system will die if the kernel is booted with "reservetop" 
>> parameter, in present code, parse "reservetop" parameter after 
>> early_ioremap_init(), and some function still use early_ioremap() 
>> after it.
> 
> btw., what are you using the 'reservetop' boot option for?
> 

Hi Ingo,

Actually, this bug is detected by my review first, then confirm it by
loading with "reservetop" parameter

>> The problem is, "reservetop" parameter can modify 'FIXADDR_TOP', 
>> then the virtual address got by early_ioremap() is base on old 
>> 'FIXADDR_TOP', but the page mapping is base on new 'FIXADDR_TOP', 
>> it will occur page fault, and the IDT is not prepare yet, so, the 
>> system is dead.
>>
>> So, put parse_early_param() in the front of early_ioremap_init() 
>> in this patch.
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
>> ---
>>  arch/x86/kernel/setup.c |   10 +++++-----
>>  1 files changed, 5 insertions(+), 5 deletions(-)
> 
> Does this bug trigger in 2.6.30 too?
> 
> I'm quite nervous about doing this change so late in the .31 cycle, 
> we've got a hundred early parameters that now get executed much 
> earlier than before. No way can i test all of them and others 
> testing it (like in your case) takes time to trickle through.
> 
> So unless this is a .31 regression i'd be inclined to queue it up 
> for .32.
> 

OK, this parameter is introduced in v2.6.27, but It seems like less
people use it and no one report this bug before. So, I think we can
queue it up for .32

Thanks,
Xiao
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