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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 B2E64C432BE for ; Wed, 11 Aug 2021 19:00:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8DAA4610A2 for ; Wed, 11 Aug 2021 19:00:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231319AbhHKTBH (ORCPT ); Wed, 11 Aug 2021 15:01:07 -0400 Received: from foss.arm.com ([217.140.110.172]:56564 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230224AbhHKTBG (ORCPT ); Wed, 11 Aug 2021 15:01:06 -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 27FADD6E; Wed, 11 Aug 2021 12:00:42 -0700 (PDT) Received: from [10.57.36.146] (unknown [10.57.36.146]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0FA263F40C; Wed, 11 Aug 2021 12:00:40 -0700 (PDT) Subject: Re: [PATCH v3 3/5] dma-iommu: add SKIP_CPU_SYNC after syncing To: David Stevens , Will Deacon Cc: Joerg Roedel , Lu Baolu , Tom Murphy , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: <20210811024247.1144246-1-stevensd@google.com> <20210811024247.1144246-4-stevensd@google.com> From: Robin Murphy Message-ID: Date: Wed, 11 Aug 2021 20:00:35 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210811024247.1144246-4-stevensd@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-08-11 03:42, David Stevens wrote: > From: David Stevens > > After syncing in map/unmap, add the DMA_ATTR_SKIP_CPU_SYNC flag so > anything that uses attrs later on will skip any sync work that has > already been completed. In particular, this skips copying from the > swiotlb twice during unmap. > > Signed-off-by: David Stevens > --- > drivers/iommu/dma-iommu.c | 13 ++++++++++--- > 1 file changed, 10 insertions(+), 3 deletions(-) > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c > index 4f0cc4a0a61f..be0214b1455c 100644 > --- a/drivers/iommu/dma-iommu.c > +++ b/drivers/iommu/dma-iommu.c > @@ -859,8 +859,11 @@ static dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page, > static void iommu_dma_unmap_page(struct device *dev, dma_addr_t dma_handle, > size_t size, enum dma_data_direction dir, unsigned long attrs) > { > - if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC)) > + if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC)) { > iommu_dma_sync_single_for_cpu(dev, dma_handle, size, dir); > + attrs |= DMA_ATTR_SKIP_CPU_SYNC; > + } > + > __iommu_dma_unmap_swiotlb(dev, dma_handle, size, dir, attrs); Again, fold that into here and put the arch sync in an else case to the is_swiotlb_buffer() check. > } > > @@ -999,8 +1002,10 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > if (dev_is_untrusted(dev)) > return iommu_dma_map_sg_swiotlb(dev, sg, nents, dir, attrs); > > - if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC)) > + if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC)) { > iommu_dma_sync_sg_for_device(dev, sg, nents, dir); > + attrs |= DMA_ATTR_SKIP_CPU_SYNC; > + } Why? attrs is never referenced again after this. > /* > * Work out how much IOVA space we need, and align the segments to > @@ -1068,8 +1073,10 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, > struct scatterlist *tmp; > int i; > > - if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC)) > + if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC)) { > iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir); > + attrs |= DMA_ATTR_SKIP_CPU_SYNC; > + } Just move it down so it's out of the SWIOTLB path entirely. Exactly like you did in patch #2 for map_sg, conspicuous in the hunk above. Robin. > > if (dev_is_untrusted(dev)) { > iommu_dma_unmap_sg_swiotlb(dev, sg, nents, dir, attrs); >