Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 94622C43381 for ; Tue, 12 Mar 2019 15:18:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6EA082054F for ; Tue, 12 Mar 2019 15:18:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726415AbfCLPSS (ORCPT ); Tue, 12 Mar 2019 11:18:18 -0400 Received: from mga05.intel.com ([192.55.52.43]:41020 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726339AbfCLPSR (ORCPT ); Tue, 12 Mar 2019 11:18:17 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Mar 2019 08:18:17 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,471,1544515200"; d="scan'208";a="133430143" Received: from ahduyck-desk1.jf.intel.com ([10.7.198.76]) by orsmga003.jf.intel.com with ESMTP; 12 Mar 2019 08:18:16 -0700 Message-ID: <67c062b183fbd5651a9aa990e677d31673ff7580.camel@linux.intel.com> Subject: Re: [PATCH] iommu/amd: fix sg->dma_address for sg->offset bigger than PAGE_SIZE From: Alexander Duyck To: Stanislaw Gruszka Cc: Rosen Penev , Joerg Roedel , Lorenzo Bianconi , linux-wireless , Samuel Sieb , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, jan.viktorin@gmail.com Date: Tue, 12 Mar 2019 08:18:16 -0700 In-Reply-To: <20190312070832.GA2483@redhat.com> References: <20190226112407.GB2989@redhat.com> <20190228090411.GA24938@redhat.com> <20190228104223.GA2749@redhat.com> <20190228121948.GD6072@redhat.com> <20190228134029.GC1594@8bytes.org> <20190304071037.GA2787@redhat.com> <20190311084319.GA3310@redhat.com> <20190311090314.GB3310@redhat.com> <20190312070832.GA2483@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On Tue, 2019-03-12 at 08:08 +0100, Stanislaw Gruszka wrote: > On Mon, Mar 11, 2019 at 08:47:44AM -0700, Alexander Duyck wrote: > > > drivers/iommu/amd_iommu.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c > > > index 6b0760dafb3e..949621f33624 100644 > > > --- a/drivers/iommu/amd_iommu.c > > > +++ b/drivers/iommu/amd_iommu.c > > > @@ -2604,7 +2604,7 @@ static int map_sg(struct device *dev, struct scatterlist *sglist, > > > > > > /* Everything is mapped - write the right values into s->dma_address */ > > > for_each_sg(sglist, s, nelems, i) { > > > - s->dma_address += address + s->offset; > > > + s->dma_address += address + (s->offset & ~PAGE_MASK); > > > s->dma_length = s->length; > > > } > > > > > > > You should add a comment calling out that this is needed because the > > sg_phys(s) call above this is masked with PAGE_MASK. Then this makes > > much more sense. Otherwise I would have assumed you needed either the > > full offset or none. > > Would something like this > > /* > * Everything is mapped - write the right values into s->dma_address. > * Take into account s->offset can be bigger than page size and sg_phys(s) > * address has to be aligned to page granularity. > */ > > be appropriate ? > > Stanislaw > No, that isn't a good description. If you take a look at the code a few lines up you find: phys_addr = (sg_phys(s) & PAGE_MASK) + (j << PAGE_SHIFT); Now if I am not mistaken the whole reason why you are having to make the change here is because the application of PAGE_MASK in this line. Basically what sg_phys() will do is take the address of the page, convert it to a physical address and add the offset. However what the mask is doing is limiting how much of that offset can be added. As a result you have to add the remainder that was masked out. So maybe a better comment would be something like: /* * Add in the remaining piece of the scatter-gather offset that was * masked out when we were determining the physical address via * (sg_phys(s) & PAGE_MASK) earlier. */