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=-15.2 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 3D790C4338F for ; Thu, 12 Aug 2021 10:38:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16AEC60FC4 for ; Thu, 12 Aug 2021 10:38:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235918AbhHLKij (ORCPT ); Thu, 12 Aug 2021 06:38:39 -0400 Received: from foss.arm.com ([217.140.110.172]:41732 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235428AbhHLKig (ORCPT ); Thu, 12 Aug 2021 06:38:36 -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 9E3761042; Thu, 12 Aug 2021 03:38:09 -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 828633F718; Thu, 12 Aug 2021 03:38:08 -0700 (PDT) Subject: Re: [PATCH v3 2/5] dma-iommu: fix arch_sync_dma for map To: David Stevens Cc: Will Deacon , Joerg Roedel , Lu Baolu , Tom Murphy , iommu@lists.linux-foundation.org, open list References: <20210811024247.1144246-1-stevensd@google.com> <20210811024247.1144246-3-stevensd@google.com> <5b4fd891-a86a-42cd-5b69-bc08d351dd3a@arm.com> From: Robin Murphy Message-ID: Date: Thu, 12 Aug 2021 11:38:02 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: 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 2021-08-12 10:21, David Stevens wrote: > On Thu, Aug 12, 2021 at 3:47 AM Robin Murphy wrote: >> >> On 2021-08-11 03:42, David Stevens wrote: >>> From: David Stevens >>> >>> When calling arch_sync_dma, we need to pass it the memory that's >>> actually being used for dma. When using swiotlb bounce buffers, this is >>> the bounce buffer. Move arch_sync_dma into the __iommu_dma_map_swiotlb >>> helper, so it can use the bounce buffer address if necessary. This also >>> means it is no longer necessary to call iommu_dma_sync_sg_for_device in >>> iommu_dma_map_sg for untrusted devices. >>> >>> Fixes: 82612d66d51d ("iommu: Allow the dma-iommu api to use bounce buffers") >>> Signed-off-by: David Stevens >>> --- >>> drivers/iommu/dma-iommu.c | 16 +++++++--------- >>> 1 file changed, 7 insertions(+), 9 deletions(-) >>> >>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c >>> index 54e103b989d9..4f0cc4a0a61f 100644 >>> --- a/drivers/iommu/dma-iommu.c >>> +++ b/drivers/iommu/dma-iommu.c >>> @@ -576,6 +576,9 @@ static dma_addr_t __iommu_dma_map_swiotlb(struct device *dev, phys_addr_t phys, >>> memset(padding_start, 0, padding_size); >>> } >>> >>> + if (!coherent && !(attrs & DMA_ATTR_SKIP_CPU_SYNC)) >> >> Make that an "else if" - otherwise you're just reintroducing the same >> thing that the third hunk is trying to clean up. > > swiotlb_tbl_map_single only copies into the swiotlb buffer, it doesn't > do any architectural syncing. So this block is necessary in the > swiotlb case as well, for iommu_dma_map_page to work properly. Urgh, apologies again - I had a mental short-circuit and was convinced that the SWIOTLB call already did its own cache maintenance. I really should have learned by now not to review fiddly patches like these while tired... > The third chunk is a separate optimization, so I'll split it out into > its own patch. It's still a logical part of this change - cleaning up the potentially wrong sync while you make sure the right one happens. Even more so if you make the fix the better way by having iommu_dma_map_sg_swiotlb() call iommu_dma_map_page(). Robin.