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 7B906C32771 for ; Wed, 22 Jan 2020 05:00:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 52F0A21835 for ; Wed, 22 Jan 2020 05:00:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725861AbgAVFAO (ORCPT ); Wed, 22 Jan 2020 00:00:14 -0500 Received: from mga01.intel.com ([192.55.52.88]:43691 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725730AbgAVFAO (ORCPT ); Wed, 22 Jan 2020 00:00:14 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Jan 2020 21:00:13 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,348,1574150400"; d="scan'208";a="215782796" Received: from allen-box.sh.intel.com (HELO [10.239.159.138]) ([10.239.159.138]) by orsmga007.jf.intel.com with ESMTP; 21 Jan 2020 21:00:11 -0800 Cc: baolu.lu@linux.intel.com, kevin.tian@intel.com, ashok.raj@intel.com, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, jacob.jun.pan@intel.com, Robin Murphy , Christoph Hellwig , Sai Praneeth Prakhya Subject: Re: [RFC PATCH 0/4] iommu: Per-group default domain type To: John Garry , Joerg Roedel , Greg Kroah-Hartman , Bjorn Helgaas References: <20200101052648.14295-1-baolu.lu@linux.intel.com> <0fbcbd62-cf8a-1c3c-c702-f9bf59497867@huawei.com> From: Lu Baolu Message-ID: <3bf07c3c-2a49-9aba-6835-53e4e80da4a2@linux.intel.com> Date: Wed, 22 Jan 2020 12:58:42 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <0fbcbd62-cf8a-1c3c-c702-f9bf59497867@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 1/21/20 6:14 PM, John Garry wrote: > On 21/01/2020 00:43, Lu Baolu wrote: >>>> An IOMMU group represents the smallest set of devices that are >>>> considered >>>> to be isolated. All devices belonging to an IOMMU group share a default >>>> domain for DMA APIs. There are two types of default domain: >>>> IOMMU_DOMAIN_DMA >>>> and IOMMU_DOMAIN_IDENTITY. The former means IOMMU translation, while >>>> the >>>> latter means IOMMU by-pass. >>>> >>>> Currently, the default domain type for the IOMMU groups is determined >>>> globally. All IOMMU groups use a single default domain type. The global >>>> default domain type can be adjusted by kernel build configuration or >>>> kernel parameters. >>>> >>>> More and more users are looking forward to a fine grained default >>>> domain >>>> type. For example, with the global default domain type set to >>>> translation, >>>> the OEM verndors or end users might want some trusted and fast-speed >>>> devices >>>> to bypass IOMMU for performance gains. On the other hand, with global >>>> default domain type set to by-pass, some devices with limited system >>>> memory addressing capability might want IOMMU translation to remove the >>>> bounce buffer overhead. >>> >>> Hi Lu Baolu, >>> >>> Do you think that it would be a more common usecase to want >>> kernel-managed devices to be passthrough for performance reasons and >>> some select devices to be in DMA domain, like those with limited >>> address cap or whose drivers request huge amounts of memory? >>> >>> I just think it would be more manageable to set kernel commandline >>> parameters for this, i.e. those select few which want DMA domain. >>> > > Hi Baolu, > >> >> It's just two sides of a coin. Currently, iommu subsystem make DMA >> domain by default, that's the reason why I selected to let user set >> which devices are willing to use identity domains. >> > > OK, understood. > > There was an alternate solution here which would allow per-group type to > be updated via sysfs: > > https://lore.kernel.org/linux-iommu/cover.1566353521.git.sai.praneeth.prakhya@intel.com/ > Yes. My patch set just tries to do this statically during boot time. > > Any idea what happened to that? No idea. Sai might have more information. :-) Best regards, baolu