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

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Date:	Wed, 25 Nov 2009 06:16:40 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	uClinux development list <uclinux-dev@...inux.org>
Cc:	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, Jie Zhang <jie.zhang@...log.com>
Subject: Re: [uClinux-dev] [PATCH] NOMMU: use copy_*_user_page() in access_process_vm()

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).

> Signed-off-by: Jie Zhang <jie.zhang@...log.com>
> Signed-off-by: Mike Frysinger <vapier@...too.org>
> ---
>  mm/nommu.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 9876fa0..51ae9be 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -1889,9 +1889,11 @@ 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, NULL,
> +					  (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, NULL,
> +					    buf, (void *) addr, len);
>  		else
>  			len = 0;
>  	} else {
--
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