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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 B22D3C46460 for ; Tue, 14 Aug 2018 08:34:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 70AC0218C3 for ; Tue, 14 Aug 2018 08:34:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 70AC0218C3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731186AbeHNLVD (ORCPT ); Tue, 14 Aug 2018 07:21:03 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:39974 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727986AbeHNLVD (ORCPT ); Tue, 14 Aug 2018 07:21:03 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id F3AF180D; Tue, 14 Aug 2018 01:34:54 -0700 (PDT) Received: from edgewater-inn.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id C563A3F5D0; Tue, 14 Aug 2018 01:34:54 -0700 (PDT) Received: by edgewater-inn.cambridge.arm.com (Postfix, from userid 1000) id 57C9F1AE3096; Tue, 14 Aug 2018 09:35:01 +0100 (BST) Date: Tue, 14 Aug 2018 09:35:01 +0100 From: Will Deacon To: "Leizhen (ThunderTown)" Cc: "Yang, Shunyong" , Robin Murphy , Jean-Philippe Brucker , Joerg Roedel , linux-arm-kernel , iommu , linux-kernel Subject: Re: [PATCH v3 4/6] iommu/io-pgtable-arm: add support for non-strict mode Message-ID: <20180814083500.GA28101@arm.com> References: <1531376312-2192-1-git-send-email-thunder.leizhen@huawei.com> <1531376312-2192-5-git-send-email-thunder.leizhen@huawei.com> <89cc2201-99ab-3f3b-a2d1-1766515d4375@arm.com> <5B597628.2020103@huawei.com> <04239cfa-bcf2-a33a-e662-ebc75e66782b@arm.com> <1d24541340334954969c58980ef85444@HXTBJIDCEMVIW01.hxtcorp.net> <5B7293E5.7040702@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5B7293E5.7040702@huawei.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 14, 2018 at 04:33:41PM +0800, Leizhen (ThunderTown) wrote: > On 2018/8/6 9:32, Yang, Shunyong wrote: > > On 2018/7/26 22:37, Robin Murphy wrote: > >> Because DMA code is not the only caller of iommu_map/unmap. It's > >> perfectly legal in the IOMMU API to partially unmap a previous mapping > >> such that a block entry needs to be split. The DMA API, however, is a > >> lot more constrined, and thus by construction the iommu-dma layer will > >> never generate a block-splitting iommu_unmap() except as a result of > >> illegal DMA API usage, and we obviously do not need to optimise for that > >> (you will get a warning about mismatched unmaps under dma-debug, but > >> it's a bit too expensive to police in the general case). > >> > > > > When I was reading the code around arm_lpae_split_blk_unmap(), I was > > curious in which scenario a block will be split. Now with your comments > > "Because DMA code is not the only caller of iommu_map/unmap", it seems > > depending on the user. > > > > Would you please explain this further? I mean besides DMA, which user > > will use iommu_map/umap and how it split a block. > > I also think that arm_lpae_split_blk_unmap() scenario is not exist, maybe > we should remove it, and give a warning for this wrong usage. Can't it happen with VFIO? Will