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 463DDC04AB1 for ; Thu, 9 May 2019 15:26:06 +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 0BD352089E for ; Thu, 9 May 2019 15:26:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0BD352089E 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]:56481 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOkvt-00008F-Al for qemu-devel@archiver.kernel.org; Thu, 09 May 2019 11:26:05 -0400 Received: from eggs.gnu.org ([209.51.188.92]:47665) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOkv7-0007z3-Iq for qemu-devel@nongnu.org; Thu, 09 May 2019 11:25:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hOkv6-00012h-0t for qemu-devel@nongnu.org; Thu, 09 May 2019 11:25:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50502) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hOkv5-0000v9-Oh for qemu-devel@nongnu.org; Thu, 09 May 2019 11:25:15 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BD6A081F35; Thu, 9 May 2019 15:25:04 +0000 (UTC) Received: from gondolin (dhcp-192-213.str.redhat.com [10.33.192.213]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7C11C5DE78; Thu, 9 May 2019 15:24:51 +0000 (UTC) Date: Thu, 9 May 2019 17:24:49 +0200 From: Cornelia Huck To: Yan Zhao Message-ID: <20190509172449.723a048b.cohuck@redhat.com> In-Reply-To: <20190508115704.GB24397@joy-OptiPlex-7040> References: <20190506014514.3555-1-yan.y.zhao@intel.com> <20190506014904.3621-1-yan.y.zhao@intel.com> <20190507111954.43d477c3.cohuck@redhat.com> <20190508115704.GB24397@joy-OptiPlex-7040> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Thu, 09 May 2019 15:25:08 +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 v2 1/2] vfio/mdev: add version 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" , "jonathan.davies@nutanix.com" , "alex.williamson@redhat.com" , "intel-gvt-dev@lists.freedesktop.org" , "Liu, Changpeng" , "linux-kernel@vger.kernel.org" , "Wang, Zhi A" , "dinechin@redhat.com" , "He, Shaopeng" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 8 May 2019 07:57:05 -0400 Yan Zhao wrote: > On Tue, May 07, 2019 at 05:19:54PM +0800, Cornelia Huck wrote: > > On Sun, 5 May 2019 21:49:04 -0400 > > Yan Zhao wrote: > > > > > version attribute is used to check two mdev devices' compatibility. > > > > > > The key point of this version attribute is that it's rw. > > > User space has no need to understand internal of device version and no > > > need to compare versions by itself. > > > Compared to reading version strings from both two mdev devices being > > > checked, user space only reads from one mdev device's version attribute. > > > After getting its version string, user space writes this string into the > > > other mdev device's version attribute. Vendor driver of mdev device > > > whose version attribute being written will check device compatibility of > > > the two mdev devices for user space and return success for compatibility > > > or errno for incompatibility. > > > > I'm still missing a bit _what_ is actually supposed to be > > compatible/incompatible. I'd assume some internal state descriptions > > (even if this is not actually limited to migration). > > > right. > originally, I thought this attribute should only contain a device's hardware > compatibility info. But seems also including vendor specific software migration > version is more reasonable, because general VFIO migration code cannot know > version of vendor specific software migration code until migration data is > transferring to the target vm. Then renaming it to migration_version is more > appropriate. > :) Nod. (...) > > > @@ -246,6 +249,143 @@ Directories and files under the sysfs for Each Physical Device > > > This attribute should show the number of devices of type that can be > > > created. > > > > > > +* version > > > + > > > + This attribute is rw, and is optional. > > > + It is used to check device compatibility between two mdev devices and is > > > + accessed in pairs between the two mdev devices being checked. > > > + The intent of this attribute is to make an mdev device's version opaque to > > > + user space, so instead of reading two mdev devices' version strings and > > > + comparing in userspace, user space should only read one mdev device's version > > > + attribute, and writes this version string into the other mdev device's version > > > + attribute. Then vendor driver of mdev device whose version attribute being > > > + written would check the incoming version string and tell user space whether > > > + the two mdev devices are compatible via return value. That's why this > > > + attribute is writable. > > > > I would reword this a bit: > > > > "This attribute provides a way to check device compatibility between > > two mdev devices from userspace. The intended usage is for userspace to > > read the version attribute from one mdev device and then writing that > > value to the version attribute of the other mdev device. The second > > mdev device indicates compatibility via the return code of the write > > operation. This makes compatibility between mdev devices completely > > vendor-defined and opaque to userspace." > > > > We still should explain _what_ compatibility we're talking about here, > > though. > > > Thanks. It's much better than mine:) > Then I'll change compatibility --> migration compatibility. Ok, with that it should be clear enough. > > > > + > > > + when reading this attribute, it should show device version string of > > > + the device of type . > > > + > > > + This string is private to vendor driver itself. Vendor driver is able to > > > + freely define format and length of device version string. > > > + e.g. It can use a combination of pciid of parent device + mdev type. > > > + > > > + When writing a string to this attribute, vendor driver should analyze this > > > + string and check whether the mdev device being identified by this string is > > > + compatible with the mdev device for this attribute. vendor driver should then > > > + return written string's length if it regards the two mdev devices are > > > + compatible; vendor driver should return negative errno if it regards the two > > > + mdev devices are not compatible. > > > + > > > + User space should treat ANY of below conditions as two mdev devices not > > > + compatible: > > > + (1) any one of the two mdev devices does not have a version attribute > > > + (2) error when read from one mdev device's version attribute > > > > s/read/reading/ > > > > > + (3) error when write one mdev device's version string to the other mdev > > > > s/write/writing/ > > > > > + device's version attribute > > > + > > > + User space should regard two mdev devices compatible when ALL of below > > > + conditions are met: > > > + (1) success when read from one mdev device's version attribute. > > > > s/read/reading/ > > > > > + (2) success when write one mdev device's version string to the other mdev > > > > s/write/writing/ > got it. thanks for pointing them out:) > > > > > + device's version attribute > > > + > > > + Errno: > > > + If vendor driver wants to claim a mdev device incompatible to all other mdev > > > > "If the vendor driver wants to designate a mdev device..." > > > ok. thanks:) > > > + devices, it should not register version attribute for this mdev device. But if > > > + a vendor driver has already registered version attribute and it wants to claim > > > + a mdev device incompatible to all other mdev devices, it needs to return > > > + -ENODEV on access to this mdev device's version attribute. > > > + If a mdev device is only incompatible to certain mdev devices, write of > > > + incompatible mdev devices's version strings to its version attribute should > > > + return -EINVAL; > > > > > > Maybe put the defined return code into a bulleted list instead? But > > this looks reasonable as well. > > > as user space have no idea of those errno and only gets 0/1 as return code from > read/write. maybe I can move this description of errno to patch 2/2 as an > example? Confused. They should get -EINVAL/-ENODEV/... all right, shouldn't they? > > > > + > > > + This attribute can be taken advantage of by live migration. > > > + If user space detects two mdev devices are compatible through version > > > + attribute, it can start migration between the two mdev devices, otherwise it > > > + should abort its migration attempts between the two mdev devices. > > > > (...) > > _______________________________________________ > > intel-gvt-dev mailing list > > intel-gvt-dev@lists.freedesktop.org > > https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev