From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:35079) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hIs0B-0001Nv-7Y for qemu-devel@nongnu.org; Tue, 23 Apr 2019 05:46:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hIs09-0000SO-Td for qemu-devel@nongnu.org; Tue, 23 Apr 2019 05:46:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55782) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hIs09-0000SA-Kg for qemu-devel@nongnu.org; Tue, 23 Apr 2019 05:46:09 -0400 Date: Tue, 23 Apr 2019 11:45:56 +0200 From: Cornelia Huck Message-ID: <20190423114556.1ef69f47.cohuck@redhat.com> In-Reply-To: <20190423054157.GA26190@joy-OptiPlex-7040> References: <20190419083258.19580-1-yan.y.zhao@intel.com> <20190419083505.19654-1-yan.y.zhao@intel.com> <20190422083950.25eb9e7c@x1.home> <20190423010152.GC32217@joy-OptiPlex-7040> <20190422192100.4d577e4b@x1.home> <20190423054157.GA26190@joy-OptiPlex-7040> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/2] vfio/mdev: add version field as mandatory attribute for mdev device List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Yan Zhao Cc: Alex Williamson , "cjia@nvidia.com" , "kvm@vger.kernel.org" , "aik@ozlabs.ru" , "Zhengxiao.zx@alibaba-inc.com" , "shuangtai.tst@alibaba-inc.com" , "qemu-devel@nongnu.org" , "kwankhede@nvidia.com" , "eauger@redhat.com" , "Liu, Yi L" , "eskultet@redhat.com" , "Yang, Ziye" , "mlevitsk@redhat.com" , "pasic@linux.ibm.com" , "libvir-list@redhat.com" , "arei.gonglei@huawei.com" , "felipe@nutanix.com" , "Ken.Xue@amd.com" , "Tian, Kevin" , "dgilbert@redhat.com" , "zhenyuw@linux.intel.com" , "intel-gvt-dev@lists.freedesktop.org" , "Liu, Changpeng" , "linux-kernel@vger.kernel.org" , "Wang, Zhi A" , "jonathan.davies@nutanix.com" , "He, Shaopeng" On Tue, 23 Apr 2019 01:41:57 -0400 Yan Zhao wrote: > On Tue, Apr 23, 2019 at 09:21:00AM +0800, Alex Williamson wrote: > > On Mon, 22 Apr 2019 21:01:52 -0400 > > Yan Zhao wrote: > > > > > On Mon, Apr 22, 2019 at 10:39:50PM +0800, Alex Williamson wrote: > > > > On Fri, 19 Apr 2019 04:35:04 -0400 > > > > Yan Zhao wrote: > > > > > > > > > device version attribute in mdev sysfs is used by user space software > > > > > (e.g. libvirt) to query device compatibility for live migration of VFIO > > > > > mdev devices. This attribute is mandatory if a mdev device supports live > > > > > migration. > > > > > > > > The Subject: doesn't quite match what's being proposed here. > > > > > > > > > It consists of two parts: common part and vendor proprietary part. > > > > > common part: 32 bit. lower 16 bits is vendor id and higher 16 bits > > > > > identifies device type. e.g., for pci device, it is > > > > > "pci vendor id" | (VFIO_DEVICE_FLAGS_PCI << 16). > > > > > > > > What purpose does this serve? If it's intended as some sort of > > > > namespace feature, shouldn't we first assume that we can only support > > > > migration to devices of the same type? Therefore each type would > > > > already have its own namespace. Also that would make the trailing bit > > > > of the version string listed below in the example redundant. A vendor > > > > is still welcome to include this in their version string if they wish, > > > > but I think the string should be entirely vendor defined. > > > > > > > hi Alex, > > > This common part is a kind of namespace. > > > Because if version string is entirely defined by vendors, I'm worried about > > > if there is a case that one vendor's version string happens to deceive and > > > interfere with another vendor's version checking? > > > e.g. > > > vendor A has a version string like: vendor id + device id + mdev type > > > vendor B has a version string like: device id + vendor id + mdev type > > > but vendor A's vendor id is 0x8086, device id is 0x1217 > > > vendor B's vendor id is 0x1217, device id is 0x8086. > > > > > > In this corner case, the two vendors may regard the two device is > > > migratable but actually they are not. > > > > > > That's the reason for this common part that serve as a kind of namespace > > > that all vendors will comply with to avoid overlap. > > > > If we assume that migration can only occur between matching mdev types, > > this is redundant, each type already has their own namespace. > > > hi Alex, > do you mean user space software like libvirt needs to first check whether > mdev type is matching and then check whether version is matching? > > if user space software only checks version for migration, it means vendor > driver has to include mdev type in their vendor proprietary part string, > right? Can't userspace simply check for the driver in use and only then check the version attribute? > Another thing is that could there be any future mdev parent driver that > applies to all mdev devices, just like vfio-pci? like Yi's vfio-pci-mdev > driver (https://lkml.org/lkml/2019/3/13/114)? Hm, I think that the vfio-pci-mdev driver then needs to expose information regarding compatibility (and not the core). 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=-0.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 47C89C10F14 for ; Tue, 23 Apr 2019 09:47:09 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1581920843 for ; Tue, 23 Apr 2019 09:47:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1581920843 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:50849 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hIs16-0001gf-9g for qemu-devel@archiver.kernel.org; Tue, 23 Apr 2019 05:47:08 -0400 Received: from eggs.gnu.org ([209.51.188.92]:35079) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hIs0B-0001Nv-7Y for qemu-devel@nongnu.org; Tue, 23 Apr 2019 05:46:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hIs09-0000SO-Td for qemu-devel@nongnu.org; Tue, 23 Apr 2019 05:46:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55782) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hIs09-0000SA-Kg for qemu-devel@nongnu.org; Tue, 23 Apr 2019 05:46:09 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 40D583007C43; Tue, 23 Apr 2019 09:46:08 +0000 (UTC) Received: from gondolin (dhcp-192-187.str.redhat.com [10.33.192.187]) by smtp.corp.redhat.com (Postfix) with ESMTP id EE6761A919; Tue, 23 Apr 2019 09:45:58 +0000 (UTC) Date: Tue, 23 Apr 2019 11:45:56 +0200 From: Cornelia Huck To: Yan Zhao Message-ID: <20190423114556.1ef69f47.cohuck@redhat.com> In-Reply-To: <20190423054157.GA26190@joy-OptiPlex-7040> References: <20190419083258.19580-1-yan.y.zhao@intel.com> <20190419083505.19654-1-yan.y.zhao@intel.com> <20190422083950.25eb9e7c@x1.home> <20190423010152.GC32217@joy-OptiPlex-7040> <20190422192100.4d577e4b@x1.home> <20190423054157.GA26190@joy-OptiPlex-7040> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Tue, 23 Apr 2019 09:46:08 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 1/2] vfio/mdev: add version field as mandatory attribute for mdev device X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "cjia@nvidia.com" , "kvm@vger.kernel.org" , "aik@ozlabs.ru" , "Zhengxiao.zx@alibaba-inc.com" , "shuangtai.tst@alibaba-inc.com" , "qemu-devel@nongnu.org" , "kwankhede@nvidia.com" , "eauger@redhat.com" , "Liu, Yi L" , "eskultet@redhat.com" , "Yang, Ziye" , "mlevitsk@redhat.com" , "pasic@linux.ibm.com" , "libvir-list@redhat.com" , "arei.gonglei@huawei.com" , "felipe@nutanix.com" , "Ken.Xue@amd.com" , "Tian, Kevin" , "dgilbert@redhat.com" , "zhenyuw@linux.intel.com" , Alex Williamson , "intel-gvt-dev@lists.freedesktop.org" , "Liu, Changpeng" , "linux-kernel@vger.kernel.org" , "Wang, Zhi A" , "jonathan.davies@nutanix.com" , "He, Shaopeng" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Message-ID: <20190423094556.3hAuF4WYsNzXLZAWFJCACkZ29FpfNMcFPtqMwrmA6mE@z> On Tue, 23 Apr 2019 01:41:57 -0400 Yan Zhao wrote: > On Tue, Apr 23, 2019 at 09:21:00AM +0800, Alex Williamson wrote: > > On Mon, 22 Apr 2019 21:01:52 -0400 > > Yan Zhao wrote: > > > > > On Mon, Apr 22, 2019 at 10:39:50PM +0800, Alex Williamson wrote: > > > > On Fri, 19 Apr 2019 04:35:04 -0400 > > > > Yan Zhao wrote: > > > > > > > > > device version attribute in mdev sysfs is used by user space software > > > > > (e.g. libvirt) to query device compatibility for live migration of VFIO > > > > > mdev devices. This attribute is mandatory if a mdev device supports live > > > > > migration. > > > > > > > > The Subject: doesn't quite match what's being proposed here. > > > > > > > > > It consists of two parts: common part and vendor proprietary part. > > > > > common part: 32 bit. lower 16 bits is vendor id and higher 16 bits > > > > > identifies device type. e.g., for pci device, it is > > > > > "pci vendor id" | (VFIO_DEVICE_FLAGS_PCI << 16). > > > > > > > > What purpose does this serve? If it's intended as some sort of > > > > namespace feature, shouldn't we first assume that we can only support > > > > migration to devices of the same type? Therefore each type would > > > > already have its own namespace. Also that would make the trailing bit > > > > of the version string listed below in the example redundant. A vendor > > > > is still welcome to include this in their version string if they wish, > > > > but I think the string should be entirely vendor defined. > > > > > > > hi Alex, > > > This common part is a kind of namespace. > > > Because if version string is entirely defined by vendors, I'm worried about > > > if there is a case that one vendor's version string happens to deceive and > > > interfere with another vendor's version checking? > > > e.g. > > > vendor A has a version string like: vendor id + device id + mdev type > > > vendor B has a version string like: device id + vendor id + mdev type > > > but vendor A's vendor id is 0x8086, device id is 0x1217 > > > vendor B's vendor id is 0x1217, device id is 0x8086. > > > > > > In this corner case, the two vendors may regard the two device is > > > migratable but actually they are not. > > > > > > That's the reason for this common part that serve as a kind of namespace > > > that all vendors will comply with to avoid overlap. > > > > If we assume that migration can only occur between matching mdev types, > > this is redundant, each type already has their own namespace. > > > hi Alex, > do you mean user space software like libvirt needs to first check whether > mdev type is matching and then check whether version is matching? > > if user space software only checks version for migration, it means vendor > driver has to include mdev type in their vendor proprietary part string, > right? Can't userspace simply check for the driver in use and only then check the version attribute? > Another thing is that could there be any future mdev parent driver that > applies to all mdev devices, just like vfio-pci? like Yi's vfio-pci-mdev > driver (https://lkml.org/lkml/2019/3/13/114)? Hm, I think that the vfio-pci-mdev driver then needs to expose information regarding compatibility (and not the core).