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

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Date:	Wed, 20 Mar 2013 23:29:05 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.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

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.

Eric
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