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 CE092C32771 for ; Wed, 22 Jan 2020 05:00:19 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A482D21835 for ; Wed, 22 Jan 2020 05:00:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A482D21835 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 6829C20764; Wed, 22 Jan 2020 05:00:19 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ElAlB2RsN3gO; Wed, 22 Jan 2020 05:00:17 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id 2F30E20495; Wed, 22 Jan 2020 05:00:17 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 186C7C0176; Wed, 22 Jan 2020 05:00:17 +0000 (UTC) Received: from fraxinus.osuosl.org (smtp4.osuosl.org [140.211.166.137]) by lists.linuxfoundation.org (Postfix) with ESMTP id 5C42AC0174 for ; Wed, 22 Jan 2020 05:00:15 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by fraxinus.osuosl.org (Postfix) with ESMTP id 3E6B785F97 for ; Wed, 22 Jan 2020 05:00:15 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from fraxinus.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id KjmV6N1KgMBT for ; Wed, 22 Jan 2020 05:00:14 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by fraxinus.osuosl.org (Postfix) with ESMTPS id 80B8E85F7F for ; Wed, 22 Jan 2020 05:00:14 +0000 (UTC) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga106.jf.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 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-Language: en-US Cc: 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 X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" 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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu