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

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Message-ID: <4B1E568A.4020005@analog.com>
Date:	Tue, 8 Dec 2009 21:37:14 +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 06:57 PM, David Howells wrote:
> Mike Frysinger<vapier@...too.org>  wrote:
>
>> +			copy_to_user_page(vma, NULL, NULL,
>> +					  (void *) addr, buf, len);
>> ...
>> +			copy_from_user_page(vma, NULL, NULL,
>> +					    buf, (void *) addr, len);
>
> I think this is not correct.  The third parameter in both cases (vaddr) is of
> unsigned long type (so should be 0 not NULL), and should not be left zero in
> any case.  I think it should be passed addr.  In fact, we should really pass
> the second parameter too (page), though for now, I'm happy to leave that NULL.
>
> See attached revision of the patch.
>
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?


Jie


> David
> ---
> From: Jie Zhang<jie.zhang@...log.com>
> Subject: [PATCH] NOMMU: Use copy_*_user_page() in access_process_vm()
>
> 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.
>
> This patch makes the reasonable assumption that copy_from_user_page() won't
> fail - which is probably fine, as we've checked the VMA from which we're
> copying is usable, and the copy is not allowed to cross VMAs.  The one case
> where it might go wrong is if the VMA is a device rather than RAM, and that
> device returns an error which - in which case rubbish will be returned rather
> than EIO.
>
> Signed-off-by: Jie Zhang<jie.zhang@...log.com>
> Signed-off-by: Mike Frysinger<vapier@...too.org>
> Signed-off-by: David Howells<dhowells@...hat.com>
> ---
>
>   mm/nommu.c |    6 ++++--
>   1 files changed, 4 insertions(+), 2 deletions(-)
>
>
> diff --git a/mm/nommu.c b/mm/nommu.c
> index af12270..953800f 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -1896,9 +1896,11 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
>
>   		/* only read or write mappings where it is permitted */
>   		if (write&&  vma->vm_flags&  VM_MAYWRITE)
> -			len -= copy_to_user((void *) addr, buf, len);
> +			copy_to_user_page(vma, NULL, addr,
> +					 (void *) addr, buf, len);
>   		else if (!write&&  vma->vm_flags&  VM_MAYREAD)
> -			len -= copy_from_user(buf, (void *) addr, len);
> +			copy_from_user_page(vma, NULL, addr,
> +					    buf, (void *) addr, len);
>   		else
>   			len = 0;
>   	} else {

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