Re: [PATCH] Increase kernel text size for x86_64

[Hannes Reinecke <hare@suse.de>]

Simon Horman wrote:
> On Wed, Aug 12, 2009 at 09:41:23AM +0200, Hannes Reinecke wrote:
>> Hi all,
>>
>> I cannot load a x86_64 kernel with kexec on 2.6.31; the error message is:
>>
>> Can't find kernel text map area from kcore
>> Cannot load /boot/vmlinuz
>>
>> Digging through the source I found a mismatch between the assumed
>> kernel text size; kexec has:
>>
>> #define KERNEL_TEXT_SIZE  (40UL*1024*1024)
>>
>> but on the kernel side we have:
>>
>> include/asm/page_64_types.h:
>> #define KERNEL_IMAGE_SIZE   (512 * 1024 * 1024)
>>
>> And, indeed, changing the definition in kexec-tools to the kernel one
>> fixed the problem.
>>
>> Not sure if this has been reported before, if so please ignore
>> the noise.
> 
> Hi,
> 
> I'm wondering what effect this would have when using
> kexec-tools with older kernels, which presumably have
> a smaller value for KERNEL_IMAGE_SIZE.
> 
>> diff --git a/kexec/arch/x86_64/crashdump-x86_64.h b/kexec/arch/x86_64/crashdump-x86_64.h
>> index 9f4dee9..0e83527 100644
>> --- a/kexec/arch/x86_64/crashdump-x86_64.h
>> +++ b/kexec/arch/x86_64/crashdump-x86_64.h
>> @@ -11,7 +11,7 @@ int load_crashdump_segments(struct kexec_info *info, char *mod_cmdline,
>>  #define MAXMEM           0x3fffffffffffUL
>>  
>>  /* Kernel text size */
>> -#define KERNEL_TEXT_SIZE  (40UL*1024*1024)
>> +#define KERNEL_TEXT_SIZE  (512UL*1024*1024)
>>  
>>  #define CRASH_MAX_MEMMAP_NR	(KEXEC_MAX_SEGMENTS + 1)
>>  #define CRASH_MAX_MEMORY_RANGES	(MAX_MEMORY_RANGES + 2)
> 
Well, the actual point of failure is in kexec/arch/x86_64/crashdump-x86_64.c:125

			/* Look for kernel text mapping header. */
			if ((saddr >= __START_KERNEL_map) &&
			    (eaddr <= __START_KERNEL_map + KERNEL_TEXT_SIZE)) {
				saddr = (saddr) & (~(KERN_VADDR_ALIGN - 1));
				info->kern_vaddr_start = saddr;
				size = eaddr - saddr;

which basically should look for a ELF header into which the kernel fits. As we're
effectively just moving the upper limit I fail to see any harm to older kernels.

Hmm. Haven't checked for other occurrences of KERNEL_TEXT_SIZE, though.

Would be nice we could be getting these values off somewhere; rely on
some kernel defines is going to break now and then.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)

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