linux-kernel - Re: [uClinux-dev] [PATCH] NOMMU: use copy_*_user_page() in access_process

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Date:	Wed, 25 Nov 2009 14:27:22 +0800
From:	Jie Zhang <jie.zhang@...log.com>
To:	Jamie Lokier <jamie@...reable.org>
CC:	uClinux development list <uclinux-dev@...inux.org>,
	David Howells <dhowells@...hat.com>,
	David McCullough <davidm@...pgear.com>,
	Greg Ungerer <gerg@...inux.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	linux-kernel@...r.kernel.org
Subject: Re: [uClinux-dev] [PATCH] NOMMU: use copy_*_user_page() in access_process_vm()

On 11/25/2009 02:16 PM, Jamie Lokier wrote:
> Mike Frysinger wrote:
>> From: Jie Zhang<jie.zhang@...log.com>
>>
>> The mmu code uses the copy_*_user_page() variants in access_process_vm()
>> rather than copy_*_user() as the former includes an icache flush.  This is
>> important when doing things like setting software breakpoints with gdb.
>> So switch the nommu code over to do the same.
>
> Reasonable, but it's a bit subtle don't you think?
> How about a one-line comment saying why it's using copy_*_user_page()?
>
> (If it was called copy_*_user_flush_icache() I wouldn't say anything,
> but it isn't).
>
But I think it's well known in Linux kernel developers that 
copy_to_user_page and copy_from_user_page should do cache flushing. It's 
documented in Documentation/cachetlb.txt. I don't think it's necessary 
to replicate it here.


Jie
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