linux-kernel - Re: [PATCH v3 18/21] vmcore: check if vmcore objects satify mmap()'s page-size boundary requirement

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Message-Id: <20130321.154650.424925595.d.hatayama@jp.fujitsu.com>
Date:	Thu, 21 Mar 2013 15:46:50 +0900 (JST)
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	ebiederm@...ssion.com
Cc:	vgoyal@...hat.com, cpw@....com, kumagai-atsushi@....nes.nec.co.jp,
	lisa.mitchell@...com, heiko.carstens@...ibm.com,
	akpm@...ux-foundation.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, zhangyanfei@...fujitsu.com
Subject: Re: [PATCH v3 18/21] vmcore: check if vmcore objects satify
 mmap()'s page-size boundary requirement

From: "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v3 18/21] vmcore: check if vmcore objects satify mmap()'s page-size boundary requirement
Date: Wed, 20 Mar 2013 23:29:05 -0700

> HATAYAMA Daisuke <d.hatayama@...fujitsu.com> writes:
>>
>> Do you mean for each range represented by each PT_LOAD entry, say:
>>
>>   [p_paddr, p_paddr + p_memsz]
>>
>> extend it as:
>>
>>   [rounddown(p_paddr, PAGE_SIZE), roundup(p_paddr + p_memsz, PAGE_SIZE)].
>>
>> not only objects in vmcore_list, but also updating p_paddr and p_memsz
>> members themselves of each PT_LOAD entry? In other words, there's no
>> new holes not referenced by any PT_LOAD entry since the regions
>> referenced by some PT_LOAD entry, themselves are extended.
> 
> No.  p_paddr and p_memsz as exported should remain the same.
> I am suggesting that we change p_offset.
> 
> I am suggesting to include the data in the file as if we had changed
> p_paddr and p_memsz.
> 
>> Then, the vmcores seen from read and mmap methods are coincide in the
>> direction of including both ranges
>>
>>   [rounddown(p_paddr, PAGE_SIZE), p_paddr]
>>
>> and
>>
>>   [p_paddr + p_memsz, roundup(p_paddr + p_memsz, PAGE_SIZE)]
>>
>> are included in both vmcores seen from read and mmap methods, although
>> they are originally not dump target memory, which you are not
>> problematic for ease of implementation.
>>
>> Is there difference here from you understanding?
> 
> Preserving the actual PT_LOAD segments p_paddr and p_memsz values is
> important. p_offset we can change as much as we want.  Which means there
> can be logical holes in the file between PT_LOAD segments, where we put
> the extra data needed to keep everything page aligned.
> 

So, I have to make the same question again. Is it OK if two vmcores
are different? How do you intend the ``extra data'' to be deal with? I
mean mmap() has to export part of old memory as the ``extra data''.

If you think OK, I'll fill the ``extra data'' with 0 in case of read
method. If not OK, I'll fill with the corresponding part of old
memory.

Thanks.
HATAYAMA, Daisuke

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