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 C99F37D2F0 for ; Fri, 31 May 2019 10:03:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726240AbfEaKDj (ORCPT ); Fri, 31 May 2019 06:03:39 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:58086 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726002AbfEaKDj (ORCPT ); Fri, 31 May 2019 06:03:39 -0400 Received: from DGGEMS414-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 9BBDB1EFB9AB272BF3AF; Fri, 31 May 2019 18:03:36 +0800 (CST) Received: from [127.0.0.1] (10.133.215.186) by DGGEMS414-HUB.china.huawei.com (10.3.19.214) with Microsoft SMTP Server id 14.3.439.0; Fri, 31 May 2019 18:03:29 +0800 Subject: Re: [PATCH v8 1/7] iommu: enhance IOMMU default DMA mode build options To: John Garry , 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 CC: Hanjun Guo , Linuxarm References: <20190530034831.4184-1-thunder.leizhen@huawei.com> <20190530034831.4184-2-thunder.leizhen@huawei.com> <645bd526-4eb0-4a36-2dda-023f009247ab@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <030bafab-58f5-8bb1-0533-2977d6e138b2@huawei.com> Date: Fri, 31 May 2019 18:03:16 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <645bd526-4eb0-4a36-2dda-023f009247ab@huawei.com> Content-Type: text/plain; charset="UTF-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.133.215.186] X-CFilter-Loop: Reflected Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 2019/5/30 20:20, John Garry wrote: > On 30/05/2019 04:48, Zhen Lei wrote: >> First, add build option IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the >> opportunity to set {lazy|strict} mode as default at build time. Then put >> the three config options in an choice, make people can only choose one of >> the three at a time. >> > > Since this was not picked up, but modulo (somtimes same) comments below: > > Reviewed-by: John Garry > >> Signed-off-by: Zhen Lei >> --- >>  drivers/iommu/Kconfig | 42 +++++++++++++++++++++++++++++++++++------- >>  drivers/iommu/iommu.c |  3 ++- >>  2 files changed, 37 insertions(+), 8 deletions(-) >> >> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig >> index 83664db5221df02..d6a1a45f80ffbf5 100644 >> --- a/drivers/iommu/Kconfig >> +++ b/drivers/iommu/Kconfig >> @@ -75,17 +75,45 @@ config IOMMU_DEBUGFS >>        debug/iommu directory, and then populate a subdirectory with >>        entries as required. >> >> -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。 > >> + >> +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? > >> + >> +endchoice >> + >>  config OF_IOMMU >>         def_bool y >>         depends on OF && IOMMU_API >> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c >> index 67ee6623f9b2a4d..56bce221285b15f 100644 >> --- a/drivers/iommu/iommu.c >> +++ b/drivers/iommu/iommu.c >> @@ -43,7 +43,8 @@ >>  #else >>  static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA; >>  #endif >> -static bool iommu_dma_strict __read_mostly = true; >> +static bool iommu_dma_strict __read_mostly = >> +            IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT); >> >>  struct iommu_group { >>      struct kobject kobj; >> > > > > . >