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=-7.6 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 7DA69C433F5 for ; Mon, 6 Sep 2021 11:06:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5A7E0606A5 for ; Mon, 6 Sep 2021 11:06:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239973AbhIFLHO (ORCPT ); Mon, 6 Sep 2021 07:07:14 -0400 Received: from foss.arm.com ([217.140.110.172]:54986 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231511AbhIFLHN (ORCPT ); Mon, 6 Sep 2021 07:07:13 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BF6486D; Mon, 6 Sep 2021 04:06:08 -0700 (PDT) Received: from [10.57.15.112] (unknown [10.57.15.112]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E01D03F73D; Mon, 6 Sep 2021 04:06:07 -0700 (PDT) Subject: Re: [git pull] IOMMU Updates for Linux v5.15 To: Joerg Roedel , Linus Torvalds Cc: iommu , Will Deacon , Linux Kernel Mailing List References: From: Robin Murphy Message-ID: <11f8773b-1440-a94a-220b-9f994241d0b4@arm.com> Date: Mon, 6 Sep 2021 12:06:02 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-09-03 22:44, Joerg Roedel wrote: > On Fri, Sep 03, 2021 at 11:43:31AM -0700, Linus Torvalds wrote: >> choice >> prompt "IOMMU default domain type" >> depends on IOMMU_API >> default IOMMU_DEFAULT_DMA_LAZY if AMD_IOMMU || INTEL_IOMMU >> default IOMMU_DEFAULT_DMA_STRICT > > Huh, yeah, that is bogus. Seems like I overlooked that part of the > patch-set because I was so amazed by the simplifications and cleanups in > the rest of it. Mad as it looks, this does in fact capture the existing behaviour. What we've consolidated here was previously a weird mix of driver- and subsystem-level controls, and it is specifically those two drivers which have a long-standing expectation of using lazy behaviour by default. >> See what I'm saying? Making the default be based on some random "this >> driver is enabled" when it can then affect *other* drivers that are >> also enabled and not part of the decision seems to be a fundamental >> confusion about what is going on, when it's not at all clear which >> driver will actually be IN USE. > > The Kconfig option itself was actually my suggestion, but how the > default value is chosen certainly needs improvement. I will sort this > out with the people involved. > >> IOW, the fix might be to just say "the default is always lazy". >> >> Or the fix might be something that is global to a configuration and >> doesn't rely on which iommu is in use (eg "on x86, the default is >> always LAZY") We could certainly express it as "default IOMMU_DEFAULT_DMA_LAZY if X86" if people would prefer - virtio-iommu doesn't support lazy mode either way, so the end result will still be equivalent. Robin. >> Or the fix is to make that 'iommu_dma_strict' variable - and the >> default value for it - be a per-IOMMU thing rather than be a global. > > My preference would be to make 'lazy' or 'strict' the default for all, > but the ARM folks might disagree. On the other side it also doesn't make > sense to let IOMMU drivers override the users Kconfig choice at runtime. > We will discuss this and come up with something better. > > Thanks, > > Joerg > _______________________________________________ > iommu mailing list > iommu@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/iommu >