From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 849787D2F0 for ; Fri, 31 May 2019 10:43:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726330AbfEaKnP (ORCPT ); Fri, 31 May 2019 06:43:15 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:43848 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726158AbfEaKnO (ORCPT ); Fri, 31 May 2019 06:43:14 -0400 Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 9228C33A72539724796A; Fri, 31 May 2019 18:43:10 +0800 (CST) Received: from [127.0.0.1] (10.202.227.238) by DGGEMS409-HUB.china.huawei.com (10.3.19.209) with Microsoft SMTP Server id 14.3.439.0; Fri, 31 May 2019 18:42:59 +0800 Subject: Re: [PATCH v8 1/7] iommu: enhance IOMMU default DMA mode build options To: "Leizhen (ThunderTown)" , "Jean-Philippe Brucker" , Robin Murphy , Will Deacon , Joerg Roedel , "Jonathan Corbet" , linux-doc , Sebastian Ott , Gerald Schaefer , "Martin Schwidefsky" , Heiko Carstens , Benjamin Herrenschmidt , Paul Mackerras , "Michael Ellerman" , Tony Luck , Fenghua Yu , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , David Woodhouse , iommu , linux-kernel , linux-s390 , linuxppc-dev , x86 , linux-ia64 References: <20190530034831.4184-1-thunder.leizhen@huawei.com> <20190530034831.4184-2-thunder.leizhen@huawei.com> <645bd526-4eb0-4a36-2dda-023f009247ab@huawei.com> <030bafab-58f5-8bb1-0533-2977d6e138b2@huawei.com> CC: Hanjun Guo , Linuxarm From: John Garry Message-ID: <55d0e30c-5bca-41fc-5bf0-4366dc387afd@huawei.com> Date: Fri, 31 May 2019 11:42:45 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <030bafab-58f5-8bb1-0533-2977d6e138b2@huawei.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.202.227.238] X-CFilter-Loop: Reflected Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org >>> -config IOMMU_DEFAULT_PASSTHROUGH >>> - bool "IOMMU passthrough by default" >>> +choice >>> + prompt "IOMMU default DMA mode" >>> depends on IOMMU_API >>> - help >>> - Enable passthrough by default, removing the need to pass in >>> - iommu.passthrough=on or iommu=pt through command line. If this >>> - is enabled, you can still disable with iommu.passthrough=off >>> - or iommu=nopt depending on the architecture. >>> + default IOMMU_DEFAULT_STRICT >>> + help >>> + This option allows IOMMU DMA mode to be chose at build time, to >> >> As before: >> /s/chose/chosen/, /s/allows IOMMU/allows an IOMMU/ > I'm sorry that the previous version was not modified. > >> >>> + override the default DMA mode of each ARCHs, removing the need to >> >> Again, as before: >> ARCHs should be singular > OK > >> >>> + pass in kernel parameters through command line. You can still use >>> + ARCHs specific boot options to override this option again. * >>> + >>> +config IOMMU_DEFAULT_PASSTHROUGH >>> + bool "passthrough" >>> + help >>> + In this mode, the DMA access through IOMMU without any addresses >>> + translation. That means, the wrong or illegal DMA access can not >>> + be caught, no error information will be reported. >>> >>> If unsure, say N here. >>> >>> +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. >> >> why no advisory on how to set if unsure? > Because the LAZY and STRICT have their own advantages and disadvantages. > > Should I say: If unsure, keep the default。 Maybe. So you could put this in the help for the choice, * above, and remove the advisory on IOMMU_DEFAULT_PASSTHROUGH. However the maintainer may have a different view. Thanks, John > >> >>> + >>> +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 the two above, but it maybe slower in some >>> + high performace scenarios. >> >> and here?