From: Harsh Jain Subject: Re: DMA error when sg->offset value is greater than PAGE_SIZE in Intel IOMMU Date: Wed, 20 Sep 2017 17:00:00 +0530 Message-ID: References: <20170920080151.GA3348@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: dwmw2@infradead.org, joro@8bytes.org, linux-crypto@vger.kernel.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, leedom@chelsio.com To: Herbert Xu Return-path: Received: from stargate.chelsio.com ([12.32.117.8]:4307 "EHLO l.chelsio.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751585AbdITLai (ORCPT ); Wed, 20 Sep 2017 07:30:38 -0400 In-Reply-To: <20170920080151.GA3348@gondor.apana.org.au> Content-Language: en-US Sender: linux-crypto-owner@vger.kernel.org List-ID: On 20-09-2017 13:31, Herbert Xu wrote: > Harsh Jain 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. > >> 2) It cannot be driver's responsibilty to update received sg entries to adjust offset and page >> because we are not the only one who directly uses received sg list. > No the driver must deal with this. Having said that, if we can > improve our driver helper interface to make this easier then we > should do that too. What we certainly shouldn't do is to take a > whack-a-mole approach like this patch does. Agreed,I added that patch for understanding purpose only. Today I referred other crypto driver for DMA related code. Most of them are using dma_map_sg except QAT. In QAT, They are first updating the Page address using offset then mapping each page in for loop with dma_map_single(0. I will try the same in chelsio driver will see the behavior. > > Cheers,