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

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Date:	Thu, 06 Jun 2013 23:31:41 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
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

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
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