linux-kernel - Re: [PATCH v8 9/9] vmcore: support mmap() on /proc/vmcore

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Date:	Fri, 07 Jun 2013 10:01:45 +0900
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	vgoyal@...hat.com, ebiederm@...ssion.com,
	akpm@...ux-foundation.org, cpw@....com,
	kumagai-atsushi@....nes.nec.co.jp, lisa.mitchell@...com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	zhangyanfei@...fujitsu.com, jingbai.ma@...com, linux-mm@...ck.org,
	riel@...hat.com, walken@...gle.com, hughd@...gle.com,
	kosaki.motohiro@...fujitsu.com
Subject: Re: [PATCH v8 9/9] vmcore: support mmap() on /proc/vmcore

(2013/06/07 6:31), Arnd Bergmann wrote:
> On Thursday 23 May 2013 14:25:48 HATAYAMA Daisuke wrote:
>> This patch introduces mmap_vmcore().
>>
>> Don't permit writable nor executable mapping even with mprotect()
>> because this mmap() is aimed at reading crash dump memory.
>> Non-writable mapping is also requirement of remap_pfn_range() when
>> mapping linear pages on non-consecutive physical pages; see
>> is_cow_mapping().
>>
>> Set VM_MIXEDMAP flag to remap memory by remap_pfn_range and by
>> remap_vmalloc_range_pertial at the same time for a single
>> vma. do_munmap() can correctly clean partially remapped vma with two
>> functions in abnormal case. See zap_pte_range(), vm_normal_page() and
>> their comments for details.
>>
>> On x86-32 PAE kernels, mmap() supports at most 16TB memory only. This
>> limitation comes from the fact that the third argument of
>> remap_pfn_range(), pfn, is of 32-bit length on x86-32: unsigned long.
>>
>> Signed-off-by: HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
>> Acked-by: Vivek Goyal <vgoyal@...hat.com>
>
> I get build errors on 'make randconfig' from this, when building
> NOMMU kernels on ARM. I suppose the new feature should be hidden
> in #ifdef CONFIG_MMU.
>
> 	Arnd
>

Thanks for trying the build and your report!

OTOH, I don't have no-MMU architectures; x86 box only. I cannot reproduce this build error. Could you give me your build log? I want to use it to detect what part depends on CONFIG_MMU.

-- 
Thanks.
HATAYAMA, Daisuke

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