linux-kernel - Re: DMA error when sg->offset value is greater than PAGE

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Date:   Tue, 26 Sep 2017 16:47:27 +0530
From:   Harsh Jain <Harsh@...lsio.com>
To:     David Woodhouse <dwmw2@...radead.org>,
        Herbert Xu <herbert@...dor.apana.org.au>
Cc:     joro@...tes.org, linux-crypto@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        leedom@...lsio.com
Subject: Re: DMA error when sg->offset value is greater than PAGE_SIZE in
 Intel IOMMU



On 26-09-2017 00:15, David Woodhouse wrote:
> On Wed, 2017-09-20 at 16:01 +0800, Herbert Xu wrote:
>> Harsh Jain <Harsh@...lsio.com> wrote:
>>>  
>>> While debugging DMA mapping error in chelsio crypto driver we
>> observed that when scatter/gather list received by driver has some
>> entry with page->offset > 4096 (PAGE_SIZE). It starts giving DMA
>> error.  Without IOMMU it works fine.
>>
>> This is not a bug.  The network stack can and will feed us such
>> SG lists.
> Hm? Under what circumstances is the offset permitted to be >
> PAGE_SIZE? 
Its random, Kernel API's don't check offset value after arithmetic operations like in "__skb_to_sgvec()", "scatterwalk_ffwd()".