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

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Date:	Thu, 16 Dec 2010 09:39:25 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Stanislaw Gruszka <sgruszka@...hat.com>,
	"H. Peter Anvin" <hpa@...or.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 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?

Thanks
Vivek

> 
> So limit it in first kernel under 512M for 32bit system.
> 
> Reported-by: Stanislaw Gruszka <sgruszka@...hat.com>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> 
> ---
>  arch/x86/kernel/setup.c |   14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6/arch/x86/kernel/setup.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/setup.c
> +++ linux-2.6/arch/x86/kernel/setup.c
> @@ -499,7 +499,19 @@ static inline unsigned long long get_tot
>  	return total << PAGE_SHIFT;
>  }
>  
> +/*
> + * arch/x86/boot/compressed/misc.c will check heap size for decompresser
> + *  32bit will have more strict limitation
> + */
>  #define DEFAULT_BZIMAGE_ADDR_MAX 0x37FFFFFF
> +#define HEAP_LIMIT_32BIT 0x20000000
> +
> +#ifdef CONFIG_X86_64
> +#define CRASH_KERNEL_LIMIT DEFAULT_BZIMAGE_ADDR_MAX
> +#else
> +#define CRASH_KERNEL_LIMIT HEAP_LIMIT_32BIT
> +#endif
> +
>  static void __init reserve_crashkernel(void)
>  {
>  	unsigned long long total_mem;
> @@ -521,7 +533,7 @@ static void __init reserve_crashkernel(v
>  		 *  kexec want bzImage is below DEFAULT_BZIMAGE_ADDR_MAX
>  		 */
>  		crash_base = memblock_find_in_range(alignment,
> -			       DEFAULT_BZIMAGE_ADDR_MAX, crash_size, alignment);
> +			       CRASH_KERNEL_LIMIT, crash_size, alignment);
>  
>  		if (crash_base == MEMBLOCK_ERROR) {
>  			pr_info("crashkernel reservation failed - No suitable area found.\n");
--
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