linux-kernel - Re: [PATCH v2 resend] kdump x86: fix total mem size calculation for reservation

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Date:	Fri, 16 Mar 2012 13:26:13 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Dave Young <dyoung@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	akpm@...ux-foundation.org, x86@...nel.org, linux@....linux.org.uk,
	vgoyal@...hat.com
Subject: Re: [PATCH v2 resend] kdump x86: fix total mem size calculation for
 reservation

On Fri, Mar 16, 2012 at 11:02:16AM +0800, Dave Young wrote:
> crashkernel reservation need know the total memory size. Current get_total_mem
> simply use max_pfn - min_low_pfn. It is wrong because it will including
> memory holes in the middle.
> 
> Especially for kvm guest with memory > 0xe0000000, there's below in qemu code:
> qemu split memory as below:
>     if (ram_size >= 0xe0000000 ) {
>         above_4g_mem_size = ram_size - 0xe0000000;
>         below_4g_mem_size = 0xe0000000;
>     } else {
>         below_4g_mem_size = ram_size;
>     }
> So for 4G mem guest, seabios will insert a 512M usable region beyond of 4G.
> Thus in above case max_pfn - min_low_pfn will be more than original memsize.
> 
> Fixing this issue by using memblock_phys_mem_size() to get the total memsize.
> 
> [v1 -> v2]: refresh the patch based on latest linus tree
> 
> Signed-off-by: Dave Young <dyoung@...hat.com>
> Reviewed-by: WANG Cong <xiyou.wangcong@...il.com>

Reviewed-by: Simon Horman <horms@...ge.net.au>

Andrew, can you pick this up?
It has been floating around without objections for a week now.

> ---
>  arch/x86/kernel/setup.c |   11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> --- linux-2.6.orig/arch/x86/kernel/setup.c	2012-03-04 03:46:35.000000000 +0800
> +++ linux-2.6/arch/x86/kernel/setup.c	2012-03-10 12:44:58.133300788 +0800
> @@ -509,15 +509,6 @@ static void __init memblock_x86_reserve_
>  
>  #ifdef CONFIG_KEXEC
>  
> -static inline unsigned long long get_total_mem(void)
> -{
> -	unsigned long long total;
> -
> -	total = max_pfn - min_low_pfn;
> -
> -	return total << PAGE_SHIFT;
> -}
> -
>  /*
>   * Keep the crash kernel below this limit.  On 32 bits earlier kernels
>   * would limit the kernel to the low 512 MiB due to mapping restrictions.
> @@ -536,7 +527,7 @@ static void __init reserve_crashkernel(v
>  	unsigned long long crash_size, crash_base;
>  	int ret;
>  
> -	total_mem = get_total_mem();
> +	total_mem = memblock_phys_mem_size();
>  
>  	ret = parse_crashkernel(boot_command_line, total_mem,
>  			&crash_size, &crash_base);
> --
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