linux-kernel - Re: [PATCH] x86_64: setup saved_max

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Date:	Thu, 2 Nov 2006 16:08:47 +0000 (GMT)
From:	Mel Gorman <mel@....ul.ie>
To:	Magnus Damm <magnus@...inux.co.jp>
Cc:	linux-kernel@...r.kernel.org, Vivek Goyal <vgoyal@...ibm.com>,
	Andi Kleen <ak@....de>, magnus.damm@...il.com,
	fastboot@...ts.osdl.org
Subject: Re: [PATCH] x86_64: setup saved_max_pfn correctly (kdump)

On Thu, 2 Nov 2006, Magnus Damm wrote:

> x86_64: setup saved_max_pfn correctly
>
> 2.6.19-rc4 has broken CONFIG_CRASH_DUMP support on x86_64. It is impossible
> to read out the kernel contents from /proc/vmcore because saved_max_pfn is set
> to zero instead of the max_pfn value before the user map is setup.
>
> This happens because saved_max_pfn is initialized at parse_early_param() time,
> and at this time no active regions have been registered. save_max_pfn is setup
> from e820_end_of_ram(), more exact find_max_pfn_with_active_regions() which
> returns 0 because no regions exist.
>
> This patch fixes this by registering before and removing after the call
> to e820_end_of_ram().
>

Hey Magnus,

I see what you are doing and why. However if you look in 
arch/x86_64/kernel/setup.c, you'll see

         parse_early_param();

         finish_e820_parsing();

         e820_register_active_regions(0, 0, -1UL);

If you just called e820_register_active_regions(0, 0, -1UL) before 
parse_early_param(), would it still fix the problem without having to call 
e820_register_active_regions(0, 0, -1UL) twice?


> Signed-off-by: Magnus Damm <magnus@...inux.co.jp>
> ---
>
> Applies to 2.6.19-rc4.
>
> arch/x86_64/kernel/e820.c |    2 ++
> 1 file changed, 2 insertions(+)
>
> --- 0002/arch/x86_64/kernel/e820.c
> +++ work/arch/x86_64/kernel/e820.c	2006-11-02 21:37:19.000000000 +0900
> @@ -594,7 +594,9 @@ static int __init parse_memmap_opt(char
> 		 * size before original memory map is
> 		 * reset.
> 		 */
> +		e820_register_active_regions(0, 0, -1UL);
> 		saved_max_pfn = e820_end_of_ram();
> +		remove_all_active_ranges();
> #endif
> 		end_pfn_map = 0;
> 		e820.nr_map = 0;
>

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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