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=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 93025C2BA19 for ; Wed, 15 Apr 2020 07:43:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6BD4320771 for ; Wed, 15 Apr 2020 07:43:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="IkfxvNbu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2635243AbgDOHn0 (ORCPT ); Wed, 15 Apr 2020 03:43:26 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:56765 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2635175AbgDOHnU (ORCPT ); Wed, 15 Apr 2020 03:43:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586936599; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1OHfgn9pPaDAsC+K8et0tvkSEtEL5Qfqe8kjye9uA/o=; b=IkfxvNbulS1k86F0O3saMwtUsHr+nbaasCbWs4evk2Ms4caJbhgEJ0p4N8jnYtGWlx7HGC d6QHg0r/0TRW2s+cF0Xy10lS+9/tpJCAHLsyG4UQpjprXZN5P2NwJ9Ujfo8svoC/Zlfyqu dHN1e/906+GRQF84NIz3AbbTYH8XXp8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-463-XK4FppVTPWSD-eyzXPObBg-1; Wed, 15 Apr 2020 03:43:17 -0400 X-MC-Unique: XK4FppVTPWSD-eyzXPObBg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4D3DD8017F5; Wed, 15 Apr 2020 07:43:14 +0000 (UTC) Received: from sturgeon (unknown [10.40.192.200]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A0F761000337; Wed, 15 Apr 2020 07:43:00 +0000 (UTC) Date: Wed, 15 Apr 2020 09:42:58 +0200 From: Erik Skultety To: Yan Zhao Cc: intel-gvt-dev@lists.freedesktop.org, cjia@nvidia.com, kvm@vger.kernel.org, linux-doc@vger.kernel.org, libvir-list@redhat.com, Zhengxiao.zx@alibaba-inc.com, shuangtai.tst@alibaba-inc.com, qemu-devel@nongnu.org, kwankhede@nvidia.com, eauger@redhat.com, corbet@lwn.net, yi.l.liu@intel.com, ziye.yang@intel.com, mlevitsk@redhat.com, pasic@linux.ibm.com, aik@ozlabs.ru, felipe@nutanix.com, Ken.Xue@amd.com, kevin.tian@intel.com, xin.zeng@intel.com, dgilbert@redhat.com, zhenyuw@linux.intel.com, dinechin@redhat.com, changpeng.liu@intel.com, cohuck@redhat.com, linux-kernel@vger.kernel.org, zhi.a.wang@intel.com, jonathan.davies@nutanix.com, shaopeng.he@intel.com Subject: Re: [PATCH v5 3/4] vfio/mdev: add migration_version attribute for mdev (under mdev device node) Message-ID: <20200415074258.GK269314@sturgeon> References: <20200413055201.27053-1-yan.y.zhao@intel.com> <20200413055504.27311-1-yan.y.zhao@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200413055504.27311-1-yan.y.zhao@intel.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Content-Transfer-Encoding: quoted-printable Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Mon, Apr 13, 2020 at 01:55:04AM -0400, Yan Zhao wrote: > migration_version attribute is used to check migration compatibility > between two mdev devices of the same mdev type. > The key is that it's rw and its data is opaque to userspace. > > Userspace reads migration_version of mdev device at source side and > writes the value to migration_version attribute of mdev device at targe= t > side. It judges migration compatibility according to whether the read > and write operations succeed or fail. > > Currently, it is able to read/write migration_version attribute under t= wo > places: > > (1) under mdev_type node > userspace is able to know whether two mdev devices are compatible befor= e > a mdev device is created. > > userspace also needs to check whether the two mdev devices are of the s= ame > mdev type before checking the migration_version attribute. It also need= s > to check device creation parameters if aggregation is supported in futu= re. > > (2) under mdev device node > userspace is able to know whether two mdev devices are compatible after > they are all created. But it does not need to check mdev type and devic= e > creation parameter for aggregation as device vendor driver would have > incorporated those information into the migration_version attribute. > > __ userspace > /\ \ > / \write > / read \ > ________/__________ ___\|/_____________ > | migration_version | | migration_version |-->check migration > --------------------- --------------------- compatibility > mdev device A mdev device B > > This patch is for mdev documentation about the second place (under > mdev device node) > > Cc: Alex Williamson > Cc: Erik Skultety > Cc: "Dr. David Alan Gilbert" > Cc: Cornelia Huck > Cc: "Tian, Kevin" > Cc: Zhenyu Wang > Cc: "Wang, Zhi A" > Cc: Neo Jia > Cc: Kirti Wankhede > Cc: Daniel P. Berrang=C3=A9 > Cc: Christophe de Dinechin > > Signed-off-by: Yan Zhao > --- > .../driver-api/vfio-mediated-device.rst | 70 +++++++++++++++++++ > 1 file changed, 70 insertions(+) > > diff --git a/Documentation/driver-api/vfio-mediated-device.rst b/Docume= ntation/driver-api/vfio-mediated-device.rst > index 2d1f3c0f3c8f..efbadfd51b7e 100644 > --- a/Documentation/driver-api/vfio-mediated-device.rst > +++ b/Documentation/driver-api/vfio-mediated-device.rst > @@ -383,6 +383,7 @@ Directories and Files Under the sysfs for Each mdev= Device > |--- remove > |--- mdev_type {link to its type} > |--- vendor-specific-attributes [optional] > + |--- migration_verion [optional] > > * remove (write only) > > @@ -394,6 +395,75 @@ Example:: > > # echo 1 > /sys/bus/mdev/devices/$mdev_UUID/remove > > +* migration_version (rw, optional) Hmm, ^this is not consistent with how patch 1/5 reports this information,= but looking at the existing docs we're not doing very well in terms of consis= tency there either. I suggest we go with "(read-write)" in both patch 1/5 and here and then s= tart the paragraph with "This is an optional attribute." > + It is used to check migration compatibility between two mdev devices= . > + Absence of this attribute means the mdev device does not support mig= ration. > + > + This attribute provides a way to check migration compatibility betwe= en two > + mdev devices from userspace after device created. The intended usage= is after the target device has been created. side note: maybe add something like "(see the migration_version attribute= of the device node if the target device already exists)" in the same section= in patch 1/5. > + for userspace to read the migration_version attribute from one mdev = device and > + then writing that value to the migration_version attribute of the ot= her mdev > + device. The second mdev device indicates compatibility via the retur= n code of > + the write operation. This makes compatibility between mdev devices c= ompletely > + vendor-defined and opaque to userspace. Userspace should do nothing = more > + than use the migration_version attribute to confirm source to target > + compatibility. ... > + > + Reading/Writing Attribute Data: > + read(2) will fail if a mdev device does not support migration and ot= herwise > + succeed and return migration_version string of the mdev device= . > + > + This migration_version string is vendor defined and opaque to = the > + userspace. Vendor is free to include whatever they feel is rel= evant. > + e.g. -. > + > + Restrictions on this migration_version string: > + 1. It should only contain ascii characters > + 2. MAX Length is PATH_MAX (4096) > + > + write(2) expects migration_version string of source mdev device, and= will > + succeed if it is determined to be compatible and otherwise fa= il with > + vendor specific errno. > + > + Errno: > + -An errno on read(2) indicates the mdev devicedoes not support migra= tion; s/devicedoes/device does/ > + -An errno on write(2) indicates the mdev devices are incompatible or= the > + target doesn't support migration. > + Vendor driver is free to define specific errno and is suggested to > + print detailed error in syslog for diagnose purpose. > + > + Userspace should treat ANY of below conditions as two mdev devices n= ot > + compatible: > + (1) any one of the two mdev devices does not have a migration_versio= n > + attribute > + (2) error when reading from migration_version attribute of one mdev = device > + (3) error when writing migration_version string of one mdev device t= o > + migration_version attribute of the other mdev device > + > + Userspace should regard two mdev devices compatible when ALL of belo= w > + conditions are met: > + (1) success when reading from migration_version attribute of one mde= v device. > + (2) success when writing migration_version string of one mdev device= to > + migration_version attribute of the other mdev device. > + > + Example Usage: > + (1) Retrieve the mdev source migration_version: > + > + # cat /sys/bus/mdev/devices/$mdev_UUID1/migration_version > + > + If reading the source migration_version generates an error, migratio= n is not > + possible. > + > + (2) Test source migration_version at target: > + > + Given a migration_version as outlined above, its compatibility to an > + instantiated device of the same mdev type can be tested as: > + # echo $VERSION > /sys/bus/mdev/devices/$mdev_UUID2/migration_versio= n > + > + If this write fails, the source and target migration versions are no= t > + compatible or the target does not support migration. > + > + > Mediated device Hot plug > ------------------------ Overall, the same comments as in 1/5 apply text-wise. Regards, -- Erik Skultety