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

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Message-ID: <20101220163118.GA2241@redhat.com>
Date:	Mon, 20 Dec 2010 17:31:19 +0100
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Yinghai Lu <yinghai@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Maxim Uvarov <muvarov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Neil Horman <nhorman@...hat.com>
Subject: Re: kdump broken on 2.6.37-rc4

On Fri, Dec 17, 2010 at 11:56:23AM -0800, H. Peter Anvin wrote:
> On 12/17/2010 11:50 AM, Vivek Goyal wrote:
> > On Fri, Dec 17, 2010 at 11:46:08AM -0800, Yinghai Lu wrote:
> >> On 12/17/2010 11:39 AM, H. Peter Anvin wrote:
> >>> On 12/17/2010 10:21 AM, Yinghai Lu wrote:
> >>>>>>
> >>>>>> Do we have actual testing for how high the 64-bit kernel will load?
> >>>>>
> >>>>> I will do some experiments on my box today and let you know.
> >>>>
> >>>> if bzImage is used, it is 896M.
> >>>>
> >>>
> >>> Why?  896 MiB is a 32-bit kernel limitation which doesn't have anything
> >>> to do with the bzImage format.
> >>>
> >>> So unless there is something going on here, I suspect you're just plain
> >>> flat wrong.
> >>
> >> kexec-tools have some checking when it loads bzImage.
> >>
> > 
> > Yinghai,
> > 
> > I think x86_64 might have just inherited the settings of 32bit without
> > giving it too much of thought. At that point of time nobody bothered
> > to load the kernel from high addresses. So these might be artificial
> > limits.
> > 
> 
> Can we do this in the meantime, just so we fix the immediate problem?
> 
> 	-hpa


I'm not sure what going on, but I can no logner reproduce kdump problem 
with -rc6 on my T-500 x86_64 system.

I tested below patch together with previous patch "x86-32: Make sure
we can map all of lowmem if we need to", and on my both laptops i686 and
x86_64 system boots and kdump works.

Stanislaw

> From 1ec83ca8dcc85bc5810bf7407d470a7261be1372 Mon Sep 17 00:00:00 2001
> From: H. Peter Anvin <hpa@...ux.intel.com>
> Date: Thu, 16 Dec 2010 19:20:41 -0800
> Subject: [PATCH] x86, kexec: Limit the crashkernel address to 768 MiB
> 
> Keep the crash kernel address below 768 MiB.  This makes it work on
> 32 bits even if the vmalloc= setting is adjusted slightly.
> 
> For 64 bits, we should be able to increase this substantially once a
> hard-coded 896 MiB limit in kexec-tools is fixed.
> 
> Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
> Cc: Vivek Goyal <vgoyal@...hat.com>
> Cc: Stanislaw Gruszka <sgruszka@...hat.com>
> Cc: Yinghai Lu <yinghai@...nel.org>
> LKML-Reference: <20101217195035.GE14502@...hat.com>
> ---
>  arch/x86/kernel/setup.c |   13 ++++++++++---
>  1 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 21c6746..2b7f5ab 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -501,7 +501,14 @@ static inline unsigned long long get_total_mem(void)
>  	return total << PAGE_SHIFT;
>  }
>  
> -#define DEFAULT_BZIMAGE_ADDR_MAX 0x37FFFFFF
> +/*
> + * Keep the crash kernel below this limit.  This should be sufficient
> + * to load a 32-bit kernel even if the vmalloc limit is modified
> + * (within reason.)  This can be increased on 64 bits once kexec-tools
> + * is fixed.
> + */
> +#define CRASH_KERNEL_ADDR_MAX	(768 << 20)
> +
>  static void __init reserve_crashkernel(void)
>  {
>  	unsigned long long total_mem;
> @@ -520,10 +527,10 @@ static void __init reserve_crashkernel(void)
>  		const unsigned long long alignment = 16<<20;	/* 16M */
>  
>  		/*
> -		 *  kexec want bzImage is below DEFAULT_BZIMAGE_ADDR_MAX
> +		 *  kexec want bzImage is below CRASH_KERNEL_ADDR_MAX
>  		 */
>  		crash_base = memblock_find_in_range(alignment,
> -			       DEFAULT_BZIMAGE_ADDR_MAX, crash_size, alignment);
> +			       CRASH_KERNEL_ADDR_MAX, crash_size, alignment);
>  
>  		if (crash_base == MEMBLOCK_ERROR) {
>  			pr_info("crashkernel reservation failed - No suitable area found.\n");
> -- 
> 1.7.2.3
> 

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