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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8F683C433F5 for ; Mon, 21 Mar 2022 11:11:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346703AbiCULNT (ORCPT ); Mon, 21 Mar 2022 07:13:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55874 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345241AbiCULNO (ORCPT ); Mon, 21 Mar 2022 07:13:14 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3BA39393E7; Mon, 21 Mar 2022 04:11:49 -0700 (PDT) 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 DF93C1042; Mon, 21 Mar 2022 04:11:48 -0700 (PDT) Received: from [10.57.43.230] (unknown [10.57.43.230]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EA0783F766; Mon, 21 Mar 2022 04:11:46 -0700 (PDT) Message-ID: Date: Mon, 21 Mar 2022 11:11:42 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH v2 2/2] thunderbolt: Make iommu_dma_protection more accurate Content-Language: en-GB To: "mika.westerberg@linux.intel.com" , "Limonciello, Mario" Cc: "joro@8bytes.org" , "baolu.lu@linux.intel.com" , "andreas.noever@gmail.com" , "michael.jamet@intel.com" , "YehezkelShB@gmail.com" , "iommu@lists.linux-foundation.org" , "linux-usb@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "hch@lst.de" References: <0dd14883930c9f55ace22162e23765a37d91a057.1647624084.git.robin.murphy@arm.com> From: Robin Murphy In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022-03-21 10:58, mika.westerberg@linux.intel.com wrote: > Hi Mario, > > On Fri, Mar 18, 2022 at 10:29:59PM +0000, Limonciello, Mario wrote: >> [Public] >> >>> Between me trying to get rid of iommu_present() and Mario wanting to >>> support the AMD equivalent of DMAR_PLATFORM_OPT_IN, scrutiny has >>> shown >>> that the iommu_dma_protection attribute is being far too optimistic. >>> Even if an IOMMU might be present for some PCI segment in the system, >>> that doesn't necessarily mean it provides translation for the device(s) >>> we care about. Furthermore, all that DMAR_PLATFORM_OPT_IN really does >>> is tell us that memory was protected before the kernel was loaded, and >>> prevent the user from disabling the intel-iommu driver entirely. While >>> that lets us assume kernel integrity, what matters for actual runtime >>> DMA protection is whether we trust individual devices, based on the >>> "external facing" property that we expect firmware to describe for >>> Thunderbolt ports. >>> >>> It's proven challenging to determine the appropriate ports accurately >>> given the variety of possible topologies, so while still not getting a >>> perfect answer, by putting enough faith in firmware we can at least get >>> a good bit closer. If we can see that any device near a Thunderbolt NHI >>> has all the requisites for Kernel DMA Protection, chances are that it >>> *is* a relevant port, but moreover that implies that firmware is playing >>> the game overall, so we'll use that to assume that all Thunderbolt ports >>> should be correctly marked and thus will end up fully protected. >>> >> >> This approach looks generally good to me. I do worry a little bit about older >> systems that didn't set ExternalFacingPort in the FW but were previously setting >> iommu_dma_protection, but I think that those could be treated on a quirk >> basis to set PCI IDs for those root ports as external facing if/when they come >> up. > > There are no such systems out there AFAICT. And even if there are, as above they've never actually been fully protected and still won't be, so it's arguably a good thing for them to stop thinking so. >> I'll send up a follow up patch that adds the AMD ACPI table check. >> If it looks good can roll it into your series for v3, or if this series goes >> as is for v2 it can come on its own. >> >>> CC: Mario Limonciello >>> Signed-off-by: Robin Murphy >>> --- >>> >>> v2: Give up trying to look for specific devices, just look for evidence >>> that firmware cares at all. >> >> I still do think you could know exactly which devices to use if you're in >> SW CM mode, but I guess the consensus is to not bifurcate the way this >> can be checked. > > Indeed. > > The patch looks good to me now. I will give it a try on a couple of > systems later today or tomorrow and let you guys know how it went. I > don't expect any problems but let's see. > > Thanks a lot Robin for working on this :) Heh, let's just hope the other half-dozen or so subsystems I need to touch for this IOMMU cleanup aren't all quite as involved as this turned out to be :) Cheers, Robin.