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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 23B76C433DF for ; Wed, 22 Jul 2020 14:00:38 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E3D072071A for ; Wed, 22 Jul 2020 14:00:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E3D072071A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=8bytes.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id BE6F388503; Wed, 22 Jul 2020 14:00:37 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id AW2Vp9+i9Vvw; Wed, 22 Jul 2020 14:00:37 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by hemlock.osuosl.org (Postfix) with ESMTP id 2BB50884D7; Wed, 22 Jul 2020 14:00:37 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1054FC004D; Wed, 22 Jul 2020 14:00:37 +0000 (UTC) Received: from fraxinus.osuosl.org (smtp4.osuosl.org [140.211.166.137]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1B6D1C004C for ; Wed, 22 Jul 2020 14:00:36 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by fraxinus.osuosl.org (Postfix) with ESMTP id 03EBA868F5 for ; Wed, 22 Jul 2020 14:00:36 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from fraxinus.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 312x_ajNYhQE for ; Wed, 22 Jul 2020 14:00:33 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from theia.8bytes.org (8bytes.org [81.169.241.247]) by fraxinus.osuosl.org (Postfix) with ESMTPS id 2A8A1868E8 for ; Wed, 22 Jul 2020 14:00:33 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id 55CD32C8; Wed, 22 Jul 2020 16:00:31 +0200 (CEST) Date: Wed, 22 Jul 2020 16:00:30 +0200 From: "joro@8bytes.org" To: "Sironi, Filippo" Subject: Re: [PATCH v2 0/3] iommu/amd: I/O VA address limits Message-ID: <20200722140029.GI27672@8bytes.org> References: <20200630093039.GC28824@8bytes.org> <20200630224634.319-1-sebott@amazon.de> <20200710123059.GF27672@8bytes.org> <751e403f-7095-f761-465b-9e187b423b0b@amazon.de> <271d67b2-482e-7a16-8fd7-1f1a6a4bdff2@arm.com> <2a04dcca86bdccece6e0109c30fc0262e1bf8829.camel@amazon.de> <004a060f-823d-af4e-a34d-1ff029faa40f@arm.com> <715c45b76f49b732e5f20157945d2ae262654602.camel@amazon.de> <20200722121922.GY27672@8bytes.org> <88c26491f2e429380028e9c04755965bc3f0341a.camel@amazon.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <88c26491f2e429380028e9c04755965bc3f0341a.camel@amazon.de> User-Agent: Mutt/1.10.1 (2018-07-13) Cc: "Serebrin, Benjamin" , "sebott@amazon.de" , "robin.murphy@arm.com" , "iommu@lists.linux-foundation.org" X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Wed, Jul 22, 2020 at 12:34:57PM +0000, Sironi, Filippo wrote: > On Wed, 2020-07-22 at 14:19 +0200, joro@8bytes.org wrote: > I wouldn't be surprised if a PCIe device raises a PCIe SERR if it is > asked to do DMA beyond its abilities. Yeah, but that would also make it impossible to safely assign the device to any untrusted entity, like a guest of user-space driver. > I think that this discussion is orthogonal wrt the spirit of the > patches. They are actually adding a few bits to the AMD IOMMU driver > (and propagating them to the right places) to implement a portion of the > specification that wasn't implemented, i.e., relying on the IVRS table. > These patches are valuable independently on the content of the IVRS > table, be it 32, 48, or 64 bits. You are right from a technical point of view, and the patches are as well. The problem I see is that there are a lot of systems out there with an AMD IOMMU and possibly broken ACPI tables. And if the driver starts checking this field now it is possible that it breaks formerly working setups. So doing this needs a strong reason, like upcoming hardware that has lower limits in the supported address space size than before. The use-case you have described is not a strong enough reason to take the risk. Regards, Joerg _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu