[PATCH] Load crash kernel high on x86

[Baoquan He]

On 09/18/15 at 08:03am, Petr Tesarik wrote:
> Hello,
> 
> There may be more than one crash kernel regions on x86. However, the kexec
> syscall checks that target address is within crashk_res boundaries. Looking
> at the logic in arch/x86/kernel/setup.c, there are only two possible layouts:
> 
>   1. crashk_res is below 4G, and there is only one region,
>   2. crashk_res is above 4G, and crashk_low_res is below 4G
> 
> In either case, kexec-tools must pick the highest region.
> 
> Currently, kexec-tools picks the largest region. If high reservation is
> smaller than low, kexec(2) returns -EADDRNOTAVAIL, and kexec prints out
> this error message:

For system with more than 4G memory, usually people won't reserve
crashkernel memory like that. But it's truly a bug and could happen in
some cases or people intend to make it happen. Sound a reasonable fix.

Ack.

> 
> kexec_load failed: Cannot assign requested address
> 
> Signed-off-by: Petr Tesarik <ptesarik at suse.com>
> ---
>  kexec/arch/i386/crashdump-x86.c | 12 ++----------
>  1 file changed, 2 insertions(+), 10 deletions(-)
> 
> diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c
> index 63959b7..2710a9e 100644
> --- a/kexec/arch/i386/crashdump-x86.c
> +++ b/kexec/arch/i386/crashdump-x86.c
> @@ -1034,16 +1034,8 @@ int get_max_crash_kernel_limit(uint64_t *start, uint64_t *end)
>  	if (!crash_reserved_mem_nr)
>  		return -1;
>  
> -	for (i = crash_reserved_mem_nr - 1; i >= 0; i--) {
> -		sz = crash_reserved_mem[i].end - crash_reserved_mem[i].start +1;
> -		if (sz <= sz_max)
> -			continue;
> -		sz_max = sz;
> -		idx = i;
> -	}
> -
> -	*start = crash_reserved_mem[idx].start;
> -	*end = crash_reserved_mem[idx].end;
> +	*start = crash_reserved_mem[crash_reserved_mem_nr - 1].start;
> +	*end = crash_reserved_mem[crash_reserved_mem_nr - 1].end;
>  
>  	return 0;
>  }
> -- 
> 2.1.4
> 
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