From mboxrd@z Thu Jan 1 00:00:00 1970 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=-13.6 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 E513BC433E6 for ; Tue, 1 Sep 2020 20:16:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C04D3206FA for ; Tue, 1 Sep 2020 20:16:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729558AbgIAUQP (ORCPT ); Tue, 1 Sep 2020 16:16:15 -0400 Received: from foss.arm.com ([217.140.110.172]:49600 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726167AbgIAUQI (ORCPT ); Tue, 1 Sep 2020 16:16:08 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 62C201063; Tue, 1 Sep 2020 13:16:07 -0700 (PDT) Received: from [10.57.40.122] (unknown [10.57.40.122]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EBC083F66F; Tue, 1 Sep 2020 13:16:04 -0700 (PDT) Subject: Re: [PATCH v9 30/32] samples: vfio-mdev/mbochs: fix common struct sg_table related issues To: Marek Szyprowski , dri-devel@lists.freedesktop.org, iommu@lists.linux-foundation.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org Cc: Christoph Hellwig , Bartlomiej Zolnierkiewicz , linux-arm-kernel@lists.infradead.org, David Airlie , Daniel Vetter , Kirti Wankhede , kvm@vger.kernel.org References: <20200826063316.23486-1-m.szyprowski@samsung.com> <20200826063316.23486-31-m.szyprowski@samsung.com> From: Robin Murphy Message-ID: <2cd26a4d-ca66-2ee8-145c-b928474fefe9@arm.com> Date: Tue, 1 Sep 2020 21:16:03 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200826063316.23486-31-m.szyprowski@samsung.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-08-26 07:33, Marek Szyprowski wrote: > The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function > returns the number of the created entries in the DMA address space. > However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and > dma_unmap_sg must be called with the original number of the entries > passed to the dma_map_sg(). > > struct sg_table is a common structure used for describing a non-contiguous > memory buffer, used commonly in the DRM and graphics subsystems. It > consists of a scatterlist with memory pages and DMA addresses (sgl entry), > as well as the number of scatterlist entries: CPU pages (orig_nents entry) > and DMA mapped pages (nents entry). > > It turned out that it was a common mistake to misuse nents and orig_nents > entries, calling DMA-mapping functions with a wrong number of entries or > ignoring the number of mapped entries returned by the dma_map_sg() > function. > > To avoid such issues, lets use a common dma-mapping wrappers operating > directly on the struct sg_table objects and use scatterlist page > iterators where possible. This, almost always, hides references to the > nents and orig_nents entries, making the code robust, easier to follow > and copy/paste safe. > > While touching this code, also add missing call to dma_unmap_sgtable. Reviewed-by: Robin Murphy > Signed-off-by: Marek Szyprowski > --- > samples/vfio-mdev/mbochs.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c > index 3cc5e5921682..e03068917273 100644 > --- a/samples/vfio-mdev/mbochs.c > +++ b/samples/vfio-mdev/mbochs.c > @@ -846,7 +846,7 @@ static struct sg_table *mbochs_map_dmabuf(struct dma_buf_attachment *at, > if (sg_alloc_table_from_pages(sg, dmabuf->pages, dmabuf->pagecount, > 0, dmabuf->mode.size, GFP_KERNEL) < 0) > goto err2; > - if (!dma_map_sg(at->dev, sg->sgl, sg->nents, direction)) > + if (dma_map_sgtable(at->dev, sg, direction, 0)) > goto err3; > > return sg; > @@ -868,6 +868,7 @@ static void mbochs_unmap_dmabuf(struct dma_buf_attachment *at, > > dev_dbg(dev, "%s: %d\n", __func__, dmabuf->id); > > + dma_unmap_sgtable(at->dev, sg, direction, 0); > sg_free_table(sg); > kfree(sg); > } >