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

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Date:	Tue, 8 Dec 2009 22:30:05 +0800
From:	Jie Zhang <jie.zhang@...log.com>
To:	David Howells <dhowells@...hat.com>
CC:	Mike Frysinger <vapier@...too.org>, uclinux-dev@...inux.org,
	David McCullough <davidm@...pgear.com>,
	Greg Ungerer <gerg@...inux.org>,
	Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org
Subject: Re: [PATCH] NOMMU: use copy_*_user_page() in access_process_vm()

On 12/08/2009 10:19 PM, David Howells wrote:
> Jie Zhang<jie.zhang@...log.com>  wrote:
>
>> I agree on using 0 instead of NULL. But for !MMU, I think, vaddr is always as
>> same as addr. So we don't need to pass it?
>
> FRV flushes the vaddr because in MMU mode the cache flush instructions take
> virtual addresses, so if we pass addr as vaddr, I can use the same cache flush
> code for both modes.  I suspect it makes little difference to the amount of
> code if we pass that rather than 0, as the value is already computed, and
> either way, it's going to take one instruction to set up the argument.
>
> Note that Blackfin assumes that it may use the dst address for flushing - an
> assumption that isn't valid in MMU mode with a VIVT cache (which I presume
> Blackfin isn't, but other CPUs are).
>
Thanks for your explanation. Now I understand why passing add as vaddr 
is better.


Jie
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