linux-kernel - Re: [PATCH v6 0/8] kdump, vmcore: support mmap() on /proc/vmcore

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Message-ID: <51958BC0.207@jp.fujitsu.com>
Date:	Fri, 17 May 2013 10:45:36 +0900
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	"H. Peter Anvin" <hpa@...or.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 v6 0/8] kdump, vmcore: support mmap() on /proc/vmcore

(2013/05/17 9:06), H. Peter Anvin wrote:
> On 05/15/2013 02:05 AM, HATAYAMA Daisuke wrote:
>> Currently, read to /proc/vmcore is done by read_oldmem() that uses
>> ioremap/iounmap per a single page. For example, if memory is 1GB,
>> ioremap/iounmap is called (1GB / 4KB)-times, that is, 262144
>> times. This causes big performance degradation.
>
> read_oldmem() is fundamentally broken and unsafe.  It needs to be
> unified with the plain /dev/mem code and any missing functionality fixed
> instead of "let's just do a whole new driver".
>
> 	-hpa

Do you mean range_is_allowed should be extended so that it checks 
according to memory map passed from the 1st kernel?

BTW, read request to read_oldmem via read_vmcore and mmap on some part 
of the 1st kernel, seems safe since it's always restrected to within the 
memory map.

Or is there other missing point?

-- 
Thanks.
HATAYAMA, Daisuke

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