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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 A80D2C468BD for ; Fri, 7 Jun 2019 12:47:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 878ED208C3 for ; Fri, 7 Jun 2019 12:47:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728412AbfFGMru (ORCPT ); Fri, 7 Jun 2019 08:47:50 -0400 Received: from foss.arm.com ([217.140.110.172]:39526 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727102AbfFGMru (ORCPT ); Fri, 7 Jun 2019 08:47:50 -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 226E53EF; Fri, 7 Jun 2019 05:47:49 -0700 (PDT) Received: from [10.1.196.129] (ostrya.cambridge.arm.com [10.1.196.129]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1E0D640151; Fri, 7 Jun 2019 05:47:47 -0700 (PDT) Subject: Re: [PATCH v8 25/29] vfio-pci: Add a new VFIO_REGION_TYPE_NESTED region type To: Auger Eric , Alex Williamson Cc: "eric.auger.pro@gmail.com" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "kvmarm@lists.cs.columbia.edu" , "joro@8bytes.org" , "jacob.jun.pan@linux.intel.com" , "yi.l.liu@intel.com" , Will Deacon , Robin Murphy , "kevin.tian@intel.com" , "ashok.raj@intel.com" , Marc Zyngier , "peter.maydell@linaro.org" , Vincent Stehle References: <20190526161004.25232-1-eric.auger@redhat.com> <20190526161004.25232-26-eric.auger@redhat.com> <20190603163159.31e7ae23@x1.home> <9c1ea2db-5ba0-3cf5-3b38-2c4a125460e6@redhat.com> From: Jean-Philippe Brucker Message-ID: <6a640710-bb9d-8923-cfef-e57786ed699f@arm.com> Date: Fri, 7 Jun 2019 13:47:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <9c1ea2db-5ba0-3cf5-3b38-2c4a125460e6@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 07/06/2019 09:28, Auger Eric wrote: >>> +static const struct vfio_pci_fault_abi fault_abi_versions[] = { >>> + [0] = { >>> + .entry_size = sizeof(struct iommu_fault), >>> + }, >>> +}; >>> + >>> +#define NR_FAULT_ABIS ARRAY_SIZE(fault_abi_versions) >> >> This looks like it's leading to some dangerous complicated code to >> support multiple user selected ABIs. How many ABIs do we plan to >> support? The region capability also exposes a type, sub-type, and >> version. How much of this could be exposed that way? ie. if we need >> to support multiple versions, expose multiple regions. > > This is something that was discussed earlier and suggested by > Jean-Philippe that we may need to support several versions of the ABI > (typicallu when adding PRI support). > Exposing multiple region is an interesting idea and I will explore that > direction. At the moment the ABI support errors and PRI. We're considering setting the fault report structure to 64 or 128 bytes (see "[PATCH v2 2/4] iommu: Introduce device fault data"). 64-byte allows for 2 additional fields before we have to introduce a new ABI version, while 128 byte should last us a while. But that's for adding new fields to existing fault types. It's probably a good idea to have different region types in VFIO for different fault types, since userspace isn't necessarily prepared to deal with them. For example right now userspace doesn't have a method to complete recoverable faults, so we can't add them to the queue. Thanks, Jean