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=-2.3 required=3.0 tests=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 BE46FC35646 for ; Fri, 21 Feb 2020 16:36:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9B9ED2067D for ; Fri, 21 Feb 2020 16:36:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726789AbgBUQgs (ORCPT ); Fri, 21 Feb 2020 11:36:48 -0500 Received: from verein.lst.de ([213.95.11.211]:56386 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726132AbgBUQgs (ORCPT ); Fri, 21 Feb 2020 11:36:48 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id BAFB768BFE; Fri, 21 Feb 2020 17:36:45 +0100 (CET) Date: Fri, 21 Feb 2020 17:36:45 +0100 From: Christoph Hellwig To: David Gibson Cc: Christoph Hellwig , Halil Pasic , "Michael S. Tsirkin" , Jason Wang , Marek Szyprowski , Robin Murphy , linux-s390@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Christian Borntraeger , Janosch Frank , Viktor Mihajlovski , Cornelia Huck , Ram Pai , Thiago Jung Bauermann , "Lendacky, Thomas" , Michael Mueller Subject: Re: [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is protected Message-ID: <20200221163645.GB10054@lst.de> References: <20200220160606.53156-1-pasic@linux.ibm.com> <20200220160606.53156-3-pasic@linux.ibm.com> <20200220161309.GB12709@lst.de> <20200221025915.GB2298@umbus.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200221025915.GB2298@umbus.fritz.box> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 21, 2020 at 01:59:15PM +1100, David Gibson wrote: > > Hell no. This is a detail of the platform DMA direct implementation. > > Drivers have no business looking at this flag, and virtio finally needs > > to be fixed to use the DMA API properly for everything but legacy devices. > > So, this patch definitely isn't right as it stands, but I'm struggling > to understand what it is you're saying is the right way. > > By "legacy devices" I assume you mean pre-virtio-1.0 devices, that > lack the F_VERSION_1 feature flag. Is that right? Because I don't > see how being a legacy device or not relates to use of the DMA API. No. "legacy" is anything that does not set F_ACCESS_PLATFORM. > I *think* what you are suggesting here is that virtio devices that > have !F_IOMMU_PLATFORM should have their dma_ops set up so that the > DMA API treats IOVA==PA, which will satisfy what the device expects. > Then the virtio driver can use the DMA API the same way for both > F_IOMMU_PLATFORM and !F_IOMMU_PLATFORM devices. No. Those should just keep using the existing legacy non-dma ops case and be done with it. No changes to that and most certainly no new features.