linux-kernel - Re: kdump broken on 2.6.37-rc4

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Date:	Thu, 16 Dec 2010 08:28:33 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	Yinghai Lu <yinghai@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Maxim Uvarov <muvarov@...il.com>, linux-kernel@...r.kernel.org,
	Neil Horman <nhorman@...hat.com>
Subject: Re: kdump broken on 2.6.37-rc4

On 12/16/2010 06:39 AM, Vivek Goyal wrote:
> On Wed, Dec 15, 2010 at 08:29:01PM -0800, Yinghai Lu wrote:
>> please check
>>
>> [PATCH] x86, crashkernel, 32bit: only try to get range under 512M
>>
>> Steanishlaw report kdump is 32bit is broken.
>>
>> in misc.c for decompresser, it will do sanity checking to make sure heap
>> heap under 512M.
> 
> Thanks Yinghai. I am wondering why on 32bit heap has to be with-in 512MB.
> I think you are referring to following check in
> arch/x86/boot/compressed/misc.c.
> 
> 	if (end > ((-__PAGE_OFFSET-(512 <<20)-1) & 0x7fffffff))
> 		error("Destination address too large");
> 
> It was introduced here.
> 
> commit 968de4f02621db35b8ae5239c8cfc6664fb872d8
> Author: Eric W. Biederman <ebiederm@...ssion.com>
> Date:   Thu Dec 7 02:14:04 2006 +0100
> 
>     [PATCH] i386: Relocatable kernel support
> 
> Eric,
> 
> It has been long. By any chance would you remember where does above
> constraint come from?
> 

It might, in fact, be bogus; specifically a proxy for the fact that we
need the kernel memory including bss and brk below the lowmem boundary,
which isn't well-defined.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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