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=-2.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, PDS_BAD_THREAD_QP_64,SPF_HELO_NONE,SPF_PASS 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 D79CFC48BE6 for ; Mon, 14 Jun 2021 09:59:43 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4D0E06023D for ; Mon, 14 Jun 2021 09:59:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4D0E06023D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nutanix.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:35992 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lsjNe-0007iI-CE for qemu-devel@archiver.kernel.org; Mon, 14 Jun 2021 05:59:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58038) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lsjLJ-0005VR-6l for qemu-devel@nongnu.org; Mon, 14 Jun 2021 05:57:17 -0400 Received: from mx0b-002c1b01.pphosted.com ([148.163.155.12]:54584) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lsjLE-00033Z-95 for qemu-devel@nongnu.org; Mon, 14 Jun 2021 05:57:16 -0400 Received: from pps.filterd (m0127841.ppops.net [127.0.0.1]) by mx0b-002c1b01.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 15E9ubIj005905; Mon, 14 Jun 2021 02:57:03 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nutanix.com; h=from : to : cc : subject : date : message-id : references : in-reply-to : content-type : content-transfer-encoding : mime-version; s=proofpoint20171006; bh=MvF/zEB7xxROMiwpj42U7+g3Q2HKmvcaicorN+c1oh4=; b=AryFZ4vE+Hh49ydeOR6fzUxvb6xNzPS1TBDvUbLFGVdFvLcl8PY1FTb8uHCAd6RYyPUs aJAvKs9ZE6SjRS+Qphm3wSYpMREhuxAeLUmIyWmmkQy+ERe6GmjEH56Yfj11VNJyk74X uj/xdNZUgivo8D0N0CMatqJQ9Yt6+Ph2OhM3MVKDMRkSWEpZrRWXkNAwVH+Sr6HmlLgr LYVSx2beufBZ98ucPqa66zrU0i7EKqyu95UskK9GybizFXp0HYkMJ2Sjg0yXFLm5oQib UgpM5EF7kCZ7hb/eJ31ozeUt8CKuwxCsZ0sfpa4rNxuJ37gAJ9czKcNRQ/M2nIAfEZ+l 1Q== Received: from nam12-mw2-obe.outbound.protection.outlook.com (mail-mw2nam12lp2049.outbound.protection.outlook.com [104.47.66.49]) by mx0b-002c1b01.pphosted.com with ESMTP id 3960du0h2c-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 14 Jun 2021 02:57:03 -0700 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=UqODfeKrDWg7J1Y+9UuoLq3tFZvEya5jrxjBx9u9CvClafUiWQk7X8YUH0ayrvQD4XuQuelY+zO0Vu2uYy7zJpNlUu64FC4Twje+2521lvAIr9F5nVgYqBw4aN/xdp3yVNuoC+vFpNo4uPH+RUkme55RS6c34pwBeqWbqLaP7sLWrs10ZA2Ev5y3rg4h4FuNYdVIj5jSjxtZIpl9JRnWmIF8IPioc4Nl2xEJHtfaO1NkF+qX94nRyEXbOlxX3tR+nXCerM4QUDCuqmpCDreKBiwcHC/71Rmv21G4teVz7ABGDBK1W8C2YUunEdy8L1BE07RVoqfCmKDDvDAmPi/6aw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=MvF/zEB7xxROMiwpj42U7+g3Q2HKmvcaicorN+c1oh4=; b=YvDVWf3uyQmW2FAVr0EmWKOttXZS7Rtc6gFDr+v2ugHaUUf1xXLJAPlBpbHvYh427q3na3e2G8mPxmh/ECKzpzPBGuToqD/V/52kxbaukB+3H7/6ef17HTWXyDQM+WOG/nBzFe2fW/7FRI2S3W5VDFl2Olf/3XN2UoBIIhSPiPx/Y48O79aXYPmBvaJOl0qn5Evvjkinsy9cmFvpL0BpW/PvbIckgTRMuFGaLM760Pbny9L5Vs7/yoSobBnHyCnDZQM9eqdwYuwzrC703qE9YP9rp0riRR3E/0+w12m2+mD0qyxslsNkivTIyuJ3gC28CGN4YOBQUUBN7sHOlg4FPg== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nutanix.com; dmarc=pass action=none header.from=nutanix.com; dkim=pass header.d=nutanix.com; arc=none Received: from CH0PR02MB7898.namprd02.prod.outlook.com (2603:10b6:610:113::5) by CH2PR02MB6599.namprd02.prod.outlook.com (2603:10b6:610:7b::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4219.24; Mon, 14 Jun 2021 09:57:01 +0000 Received: from CH0PR02MB7898.namprd02.prod.outlook.com ([fe80::a91d:ad88:5b1f:c981]) by CH0PR02MB7898.namprd02.prod.outlook.com ([fe80::a91d:ad88:5b1f:c981%7]) with mapi id 15.20.4219.025; Mon, 14 Jun 2021 09:57:00 +0000 From: Thanos Makatos To: John Levon , Stefan Hajnoczi Subject: RE: [PATCH v8] introduce vfio-user protocol specification Thread-Topic: [PATCH v8] introduce vfio-user protocol specification Thread-Index: AQHXMSMjtDp7nXmGRkuiYMGnZrvqnqrTdveAgAALLYCAQCC3YA== Date: Mon, 14 Jun 2021 09:57:00 +0000 Message-ID: References: <20210414114122.236193-1-thanos.makatos@nutanix.com> <20210504143141.GA1078723@sent> In-Reply-To: <20210504143141.GA1078723@sent> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: nutanix.com; dkim=none (message not signed) header.d=none;nutanix.com; dmarc=none action=none header.from=nutanix.com; x-originating-ip: [78.149.4.199] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 7210cab9-d442-4d57-b0c0-08d92f1ac156 x-ms-traffictypediagnostic: CH2PR02MB6599: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-proofpoint-crosstenant: true x-ms-oob-tlc-oobclassifiers: OLM:10000; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: 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 x-forefront-antispam-report: CIP:255.255.255.255; CTRY:; LANG:en; SCL:1; SRV:; IPV:NLI; SFV:NSPM; H:CH0PR02MB7898.namprd02.prod.outlook.com; PTR:; CAT:NONE; SFS:(39860400002)(136003)(396003)(366004)(346002)(376002)(33656002)(8676002)(8936002)(7696005)(2906002)(26005)(71200400001)(55236004)(54906003)(316002)(7416002)(110136005)(6506007)(186003)(44832011)(83380400001)(86362001)(76116006)(52536014)(5660300002)(66476007)(66946007)(9686003)(66556008)(64756008)(38100700002)(55016002)(66446008)(122000001)(4326008)(478600001); DIR:OUT; SFP:1102; x-ms-exchange-antispam-messagedata-chunkcount: 1 x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?/JbPyraCZWpAfTQDbdfQhn20JMcSK2dRm07uALOvVH7hrKS0VvsVIGMmP7m8?= =?us-ascii?Q?jh3CEEXdnHVTvs5RVV0Mrg0X9lJ1dZQgm8z99WcUTKqJOFHrhy0kJl3rs8l+?= =?us-ascii?Q?IQeP5ejp8Yy4vjAE7D5jsl1isQajwxnW2ymYtOUb/FTdEVTLt+Mcibcv6XNQ?= =?us-ascii?Q?KluvsIRbShlFAhU+gR4YwoemoMh+wawipWI3d7wG2bGnGAUxJRmz4VIJmbaJ?= =?us-ascii?Q?0e/MRoL7sdOMT5haX6J7zgFhe5pHBeHgpdICsBLaeZPOKeD+khCtTP411C+L?= =?us-ascii?Q?EQTvLmTmIsvrtOKzYWv2C8yXt8/okwzTHl4rYmwQAtWgpsZgEr7PFyON3CiA?= =?us-ascii?Q?Hka3Z9KoULekPdBP3nIzoJlES0l/MulKcxZ/2UPGl9yRGbZvq9W6Kaade6p3?= =?us-ascii?Q?iwwrjrzU3u8mlkug2hp0Xi1gYy6RVTrLRpbXoZxRjJrbjvqNr3+yqnxospPs?= =?us-ascii?Q?MrRZmr9QJQ/BkkB5FKKRVPWIlG026vx4Xvp0cgbAFVLaG6fjhwt9OyJj0bXE?= =?us-ascii?Q?Xc6Rz2s8GJlV8It2LnfPXRiZIAfnoWboewo5HHlizp8HhJc13SACLPbaRQVl?= =?us-ascii?Q?KVMYqgdNGdMx2qDeWScG93Oq3wOtUYt1SINUK3+fATGrNHnoFoqg27emrT9C?= =?us-ascii?Q?ds5OPBgDc2E3TO2wk+hK9tCK0B3P231TwO69qgaDrWpTLkrytlH3tOQNUA3U?= =?us-ascii?Q?EyCBIvUIhPPdEJhCROuErlMZozQ29sSBZf4SdEE7/XkmNnXyqCE/CRQWaY+P?= =?us-ascii?Q?yqN9FaK/ibu71DVxdvf3i8ezxgjGqVdL3kb8yEhOoUJUJnvSMTyoamBuEdgR?= =?us-ascii?Q?mwbyBtwR8BKUDocK7+ZdiT0ZaRg2eYL5heXgWKlur5Zfa9tuvQWop0jHx7ne?= =?us-ascii?Q?+oJ2PTeZsoBbG/78zIwUqisPZTkIIlOgVxnjK7WntqJBsf2KefdMAPT42Hr2?= =?us-ascii?Q?uDexZHNLpmOmo0No5g8ZSWUg5I7SQuGWh6IZ0yqY0iOJMlpzOSHdY+k/ANbO?= =?us-ascii?Q?LmiVVIgJGGF23tpAUGhd5DtEVJC2/RmrNXbObf8wUqqatr0gOFFMxFMwvRfz?= =?us-ascii?Q?1sV8QNhNv9NiORKPU/volmNCEgnPpjctmX3QiBRuZVnC5ouLvamde2tJpH6c?= =?us-ascii?Q?YFOorwlHILOzKgPSJ0ilzR1dGtfaCHc6mVqWJieNkCGd3Q1pM1QlMxPR5QQ+?= =?us-ascii?Q?2Kplo+Eg0kQKnl54VZaQrK38r9ntekFdV9ZX4LDqOYM2jBHA4g0VhmnN0nJA?= =?us-ascii?Q?XipMShRlK+HelAxN9wqHKcfdf9LljvMWM8VFZrsV164JLLhywC2oKITaoUNu?= =?us-ascii?Q?zO8=3D?= Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: nutanix.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: CH0PR02MB7898.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 7210cab9-d442-4d57-b0c0-08d92f1ac156 X-MS-Exchange-CrossTenant-originalarrivaltime: 14 Jun 2021 09:57:00.6874 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: bb047546-786f-4de1-bd75-24e5b6f79043 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: zODzYS2PDGeE6dLfmqRW213OqLcGB9NvYp1LgV3PLgAea10J21cz7d9VkK0dywGZXy5U0YYmWo/kvy/xBOa/DaiBZtFX/cb2neo1WID9PJg= X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR02MB6599 X-Proofpoint-GUID: JVfdItaYmrOA5GN5BI34p8vbkROfaNyg X-Proofpoint-ORIG-GUID: JVfdItaYmrOA5GN5BI34p8vbkROfaNyg X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391, 18.0.761 definitions=2021-06-14_04:2021-06-11, 2021-06-14 signatures=0 X-Proofpoint-Spam-Reason: safe Received-SPF: pass client-ip=148.163.155.12; envelope-from=thanos.makatos@nutanix.com; helo=mx0b-002c1b01.pphosted.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.199, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "benjamin.walker@intel.com" , John G Johnson , Swapnil Ingle , "Michael S . Tsirkin" , Jason Wang , "qemu-devel@nongnu.org" , John Levon , Kirti Wankhede , Gerd Hoffmann , "tina.zhang@intel.com" , "jag.raman@oracle.com" , "james.r.harris@intel.com" , Elena Ufimtseva , "Kanth.Ghatraju@oracle.com" , Felipe Franciosi , "marcandre.lureau@redhat.com" , Christophe de Dinechin , Yan Zhao , "konrad.wilk@oracle.com" , "yuvalkashtan@gmail.com" , "dgilbert@redhat.com" , "ismael@linux.com" , "changpeng.liu@intel.com" , "tomassetti.andrea@gmail.com" , "mpiszczek@ddn.com" , Cornelia Huck , "alex.williamson@redhat.com" , Raphael Norwitz , "xiuchun.lu@intel.com" , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" > > Are there rules for avoiding deadlock between client->server and > > server->client messages? For example, the client sends > > VFIO_USER_REGION_WRITE and the server sends > VFIO_USER_VM_INTERRUPT > > before replying to the write message. > > > > Multi-threaded clients and servers could end up deadlocking if > > messages are processed while polling threads handle other device activi= ty > (e.g. > > I/O requests that cause DMA messages). > > > > Pipelining has the nice effect that the oldest message must complete > > before the next pipelined message starts. It imposes a maximum issue > > depth of 1. Still, it seems like it would be relatively easy to hit > > re-entrancy or deadlock issues since both the client and the server > > can initiate messages and may need to wait for a response. >=20 > It's certainly the case that implementation-wise right now these are issu= es, at > least on the library side. I think I'm probably OK with requiring respons= es to > be provided prior to async messages like VM_INTERRUPT. I think re-entrancy/deadblock issues are not spec-related but can be implem= entation specific. In your example, the client can't assume that simply because it sent a REGI= ON_WRITE message the only message the server will send will be the reply: it might a= s well be a VM_INTERRUPT or DMA_READ message.