netdev - Re: [RFC PATCH 00/10] Remove skb_dma

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Message-ID: <20091125113050.GA19837@serverengines.com>
Date:	Wed, 25 Nov 2009 17:00:51 +0530
From:	Ajit Khaparde <ajitkhaparde@...il.com>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	mcarlson@...adcom.com, mchan@...adcom.com,
	sathyap@...verengines.com, subbus@...verengines.com,
	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 00/10] Remove skb_dma_map/unmap calls

On 24/11/09 17:20 -0800, Alexander Duyck wrote:
> This patch series removes the skb_dma_map and skb_dma_unmap function calls.
> The reason for this change is because the use of skb_dma_map/unmap can lead
> to serious issues when HW IOMMU is enabled.  This is because each mapping
> of the skb with a HW IOMMU enabled results in a new set of DMA mappings.
> This in turn leads to issues when skbs are cloned for uses such as
> bridging or pktgen because each transmitting device will update the skb
> shared info structure resulting in some mappings being overwritten, and others
> being freed multiple times.

If this is the case can the members related to the dma mapping stuff
(skb_shinfo(skb)->dma_maps) be moved out of this shared info structure and
we retain this "good" abstraction provided by this skb_dma_map/unmap api?
> 
> I am looking for input specifically on the tg3, be2net, and bnx2 driver
> patches as I am not very familiar with them and I am not certain if
> additional changes are required.

>       be2net: remove use of skb_dma_map/unmap
> 
>  drivers/net/benet/be_main.c    |   37 ++++++---

We have pulled the be2net specific patch for testing and review.
We will send an update once done with it.

-Ajit
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