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=-15.3 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,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 7167AC48BCD for ; Wed, 9 Jun 2021 15:30:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 510AF611CC for ; Wed, 9 Jun 2021 15:30:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236410AbhFIPcD (ORCPT ); Wed, 9 Jun 2021 11:32:03 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:3190 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233476AbhFIPcB (ORCPT ); Wed, 9 Jun 2021 11:32:01 -0400 Received: from fraeml711-chm.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4G0W1T6RGvz6J9WM; Wed, 9 Jun 2021 23:17:17 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml711-chm.china.huawei.com (10.206.15.60) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Wed, 9 Jun 2021 17:30:04 +0200 Received: from [10.47.80.201] (10.47.80.201) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Wed, 9 Jun 2021 16:30:03 +0100 Subject: Re: [PATCH v11 1/3] iommu: Enhance IOMMU default DMA mode build options To: Robin Murphy , , , , CC: , , , References: <1623158308-180604-1-git-send-email-john.garry@huawei.com> <1623158308-180604-2-git-send-email-john.garry@huawei.com> From: John Garry Message-ID: Date: Wed, 9 Jun 2021 16:24:09 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.47.80.201] X-ClientProxiedBy: lhreml749-chm.china.huawei.com (10.201.108.199) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/06/2021 16:03, Robin Murphy wrote: > On 2021-06-08 14:18, John Garry wrote: >> From: Zhen Lei >> >> First, add build options IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the >> opportunity to set {lazy|strict} mode as default at build time. Then put >> the two config options in a choice, as they are mutually exclusive. >> >> [jpg: Make choice between strict and lazy only (and not passthrough)] >> Signed-off-by: Zhen Lei >> Signed-off-by: John Garry >> --- >>   drivers/iommu/Kconfig | 35 +++++++++++++++++++++++++++++++++++ >>   drivers/iommu/iommu.c |  3 ++- >>   2 files changed, 37 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig >> index 1f111b399bca..369a3af9e5bf 100644 >> --- a/drivers/iommu/Kconfig >> +++ b/drivers/iommu/Kconfig >> @@ -90,6 +90,41 @@ config IOMMU_DEFAULT_PASSTHROUGH >>         If unsure, say N here. >> +choice >> +    prompt "IOMMU default DMA mode" >> +    depends on IOMMU_API >> +    depends on X86 || IA64 || X86_64 || ARM || ARM64 > > Simply "depends on IOMMU_DMA" should suffice, since that's now the only > place where flush queues matter. I suppose so. Configs ARM64, AMD_IOMMU, and INTEL_IOMMU all select this. > >> + >> +    default IOMMU_DEFAULT_STRICT >> +    help >> +      This option allows an IOMMU DMA mode to be chosen at build >> time, to >> +      override the default DMA mode of each ARCH, removing the need to >> +      pass in kernel parameters through command line. It is still >> possible >> +      to provide ARCH-specific or common boot options to override this >> +      option. >> + >> +      If unsure, keep the default. >> + >> +config IOMMU_DEFAULT_LAZY >> +    bool "lazy" >> +    help >> +      Support lazy mode, where for every IOMMU DMA unmap operation, the >> +      flush operation of IOTLB and the free operation of IOVA are >> deferred. >> +      They are only guaranteed to be done before the related IOVA >> will be >> +      reused. >> + >> +config IOMMU_DEFAULT_STRICT >> +    bool "strict" >> +    help >> +      For every IOMMU DMA unmap operation, the flush operation of >> IOTLB and >> +      the free operation of IOVA are guaranteed to be done in the unmap >> +      function. >> + >> +      This mode is safer than lazy mode, but it may be slower in some >> high >> +      performance scenarios. > > FWIW, as an end user who doesn't care much about the implementation > details I'd probably appreciate the actual implications being clearer, > i.e. what does "safer" mean in practice and what is it relative to? > Fine, I can mention that lazy mode means that we have reduced device isolation and a dangerous window can be created between device driver DMA unmap and zapping the mapping in the IOMMU; however still much safer than passthrough/no IOMMU, which means no isolation at all. Thanks, John