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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 9933CC17442 for ; Wed, 13 Nov 2019 07:03:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C03A222C6 for ; Wed, 13 Nov 2019 07:03:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726564AbfKMHDU (ORCPT ); Wed, 13 Nov 2019 02:03:20 -0500 Received: from verein.lst.de ([213.95.11.211]:60684 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726074AbfKMHDT (ORCPT ); Wed, 13 Nov 2019 02:03:19 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 3AA5868C4E; Wed, 13 Nov 2019 08:03:13 +0100 (CET) Date: Wed, 13 Nov 2019 08:03:12 +0100 From: Christoph Hellwig To: Lu Baolu Cc: Christoph Hellwig , David Woodhouse , Joerg Roedel , Bjorn Helgaas , ashok.raj@intel.com, jacob.jun.pan@intel.com, alan.cox@intel.com, kevin.tian@intel.com, mika.westerberg@linux.intel.com, Ingo Molnar , Greg Kroah-Hartman , pengfei.xu@intel.com, Konrad Rzeszutek Wilk , Marek Szyprowski , Robin Murphy , Jonathan Corbet , Boris Ostrovsky , Juergen Gross , Stefano Stabellini , Steven Rostedt , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Jacob Pan Subject: Re: [PATCH v5 02/10] iommu/vt-d: Use per-device dma_ops Message-ID: <20191113070312.GA2735@lst.de> References: <20190725031717.32317-1-baolu.lu@linux.intel.com> <20190725031717.32317-3-baolu.lu@linux.intel.com> <20190725054413.GC24527@lst.de> <20190725114348.GA30957@lst.de> <20191112071640.GA3343@lst.de> <0885617e-8390-6d18-987f-40d49f9f563e@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0885617e-8390-6d18-987f-40d49f9f563e@linux.intel.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 13, 2019 at 10:50:27AM +0800, Lu Baolu wrote: > Currently, this is a block issue for using per-device dma ops in Intel > IOMMU driver. Hence block this driver from using the generic iommu dma > ops. That is in fact the reason why I bring it up :) > I'd like to align Intel IOMMU driver with other vendors. Use iommu dma > ops for devices which have been selected to go through iommu. And use > direct dma ops if selected to by pass. > > One concern of this propose is that for devices with limited address > capability, shall we force it to use iommu or alternatively use swiotlb > if user decides to let it by pass iommu. > > I understand that using swiotlb will cause some overhead due to the > bounced buffer, but Intel IOMMU is default on hence any users who use a > default kernel won't suffer this. We only need to document this so that > users understand this overhead when they decide to let such devices by > pass iommu. This is common to all vendor iommu drivers as far as I can > see. Indeed. And one idea would be to lift the code in the powerpc dma_iommu_ops that check a flag and use the direct ops to the generic dma code and a flag in struct device. We can then switch the intel iommu ops (and AMD Gart) over to it.