linux-kernel - Re: [PATCH 2/4] iovmm: fix roundup for next area and end check for the last area

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Date:	Fri, 1 Oct 2010 13:57:11 +0300
From:	David Cohen <david.cohen@...ia.com>
To:	ext Fernando Guzman Lugo <x0095840@...com>
Cc:	"Doyu Hiroshi (Nokia-MS/Espoo)" <hiroshi.doyu@...ia.com>,
	"Contreras Felipe (Nokia-MS/Helsinki)" <felipe.contreras@...ia.com>,
	"Palande Ameya (Nokia-MS/Helsinki)" <ameya.palande@...ia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 2/4] iovmm: fix roundup for next area and end check for
 the last area

Hi,

On Fri, Oct 01, 2010 at 05:08:53AM +0200, ext Fernando Guzman Lugo wrote:
> As da_end does not belongs to the area the roundup should
> be done to da_end and not to da_end + 1.
> Also the end check for the last area should be
> ULONG_MAX - start + 1 >= bytes.
> 
> Signed-off-by: Fernando Guzman Lugo <x0095840@...com>
> ---
>  arch/arm/plat-omap/iovmm.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/plat-omap/iovmm.c b/arch/arm/plat-omap/iovmm.c
> index 24ca9c4..fc6b109 100644
> --- a/arch/arm/plat-omap/iovmm.c
> +++ b/arch/arm/plat-omap/iovmm.c
> @@ -289,19 +289,19 @@ static struct iovm_struct *alloc_iovm_area(struct iommu *obj, u32 da,
>  	prev_end = 0;
>  	list_for_each_entry(tmp, &obj->mmap, list) {
>  
> -		if (prev_end >= start)
> +		if (prev_end > start)
>  			break;
>  
>  		if (start + bytes <= tmp->da_start)
>  			goto found;
>  
>  		if (flags & IOVMF_DA_ANON)
> -			start = roundup(tmp->da_end + 1, alignement);
> +			start = roundup(tmp->da_end, alignement);

There's a lack of comment here, but the purpose of tmp->da_end + 1 is to
create a gap between iovm areas to force to trigger iommu faults when
some access exceeds a valid area. Without this gap, such situation
may produce data corruption which is much more difficult to track.

Br,

David

>  
>  		prev_end = tmp->da_end;
>  	}
>  
> -	if ((start > prev_end) && (ULONG_MAX - start >= bytes))
> +	if ((start >= prev_end) && (ULONG_MAX - start + 1 >= bytes))
>  		goto found;
>  
>  	dev_dbg(obj->dev, "%s: no space to fit %08x(%x) flags: %08x\n",
> -- 
> 1.6.3.3
> 
> --
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