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=-10.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 9A716C433E0 for ; Mon, 22 Feb 2021 13:13:09 +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 0E06164E29 for ; Mon, 22 Feb 2021 13:13:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0E06164E29 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 ([::1]:57236 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lEB1P-0003tv-1x for qemu-devel@archiver.kernel.org; Mon, 22 Feb 2021 08:13:07 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:56678) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lEAvp-0006s6-2i for qemu-devel@nongnu.org; Mon, 22 Feb 2021 08:07:21 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:55964) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lEAvm-0005fe-8u for qemu-devel@nongnu.org; Mon, 22 Feb 2021 08:07:19 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613999237; 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=CVdQS4ZUFYmOzxPgo/LPDPHKA/fjXwUZADeXIBLujvY=; b=H/bgALEkQQKw3gUD2Ada/mFk2xhmlioQFgGlS8BgraaAQFv3O59gIuYjkPqnxmX3Gn9dPr jT4tuMxRH9XCW+8FErxoFvkPrjx1bgHjFEBQh/i9RYzwhlTnSjBRRUgrDLiKB8BOjp4BiX z+CyQPrXa8E9Cpl327YXJsgSvQ7PRiQ= 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-555-rn4tXKUwPf2LqBw11ihHPQ-1; Mon, 22 Feb 2021 08:06:30 -0500 X-MC-Unique: rn4tXKUwPf2LqBw11ihHPQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 52918801965; Mon, 22 Feb 2021 13:06:26 +0000 (UTC) Received: from work-vm (ovpn-115-14.ams2.redhat.com [10.36.115.14]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0CE6D189A4; Mon, 22 Feb 2021 13:06:09 +0000 (UTC) Date: Mon, 22 Feb 2021 13:06:07 +0000 From: "Dr. David Alan Gilbert" To: Alex =?iso-8859-1?Q?Benn=E9e?= Subject: Re: vhost reply_ack negotiation (a.k.a differences in vhost-user behaviour with libvhost-user and vhost-user-backend.rs) Message-ID: References: <8735xskm7j.fsf@linaro.org> MIME-Version: 1.0 In-Reply-To: <8735xskm7j.fsf@linaro.org> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: Sergio Lopez , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Stefan Hajnoczi , "rust-vmm@lists.opendev.org" , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Alex Bennée (alex.bennee@linaro.org) wrote: > Hi, > > I finally got a chance to get down into the guts of vhost-user while > attempting to port my original C RPMB daemon to Rust using the > vhost-user-backend and related crates. I ended up with this hang during > negotiation: > > startup > > vhost_user_write req:1 flags:0x1 > vhost_user_read_start > vhost_user_read req:1 flags:0x5 > vhost_user_backend_init: we got 170000000 > vhost_user_write req:15 flags:0x1 > vhost_user_read_start > vhost_user_read req:15 flags:0x5 > vhost_user_set_protocol_features: 2008 > vhost_user_write req:16 flags:0x1 > vhost_user_write req:3 flags:0x1 > vhost_user_write req:1 flags:0x1 > vhost_user_read_start > vhost_user_read req:1 flags:0x5 > vhost_user_write req:13 flags:0x1 > > kernel initialises device > > virtio_rpmb virtio1: init done! > vhost_user_write req:13 flags:0x1 > vhost_dev_set_features: 130000000 > vhost_user_set_features: 130000000 > vhost_user_write req:2 flags:0x1 > vhost_user_write req:5 flags:0x9 > vhost_user_read_start > > The proximate cause is the vhost crate handling: > > MasterReq::SET_MEM_TABLE => { > let res = self.set_mem_table(&hdr, size, &buf, rfds); > self.send_ack_message(&hdr, res)?; > } > > which gates on the replay_ack_enabled flag: > > fn send_ack_message( > &mut self, > req: &VhostUserMsgHeader, > res: Result<()>, > ) -> Result<()> { > if dbg!(self.reply_ack_enabled) { > let hdr = self.new_reply_header::(req, 0)?; > let val = match res { > Ok(_) => 0, > Err(_) => 1, > }; > let msg = VhostUserU64::new(val); > self.main_sock.send_message(&hdr, &msg, None)?; > } > Ok(()) > } > > which is only set when we have all the appropriate acknowledged flags: > > fn update_reply_ack_flag(&mut self) { > let vflag = VhostUserVirtioFeatures::PROTOCOL_FEATURES.bits(); > let pflag = VhostUserProtocolFeatures::REPLY_ACK; > if (self.virtio_features & vflag) != 0 > && (self.acked_virtio_features & vflag) != 0 > && self.protocol_features.contains(pflag) > && (self.acked_protocol_features & pflag.bits()) != 0 > { > self.reply_ack_enabled = true; > } else { > self.reply_ack_enabled = false; > } > } > > which from above you can see QEMU helpfully dropped those bits in the > reply. It does however work in the C/libvhost version: > > virtio_rpmb virtio1: init done! > vhost_user_write req:13 flags:0x1 > vhost_dev_set_features: 130000000 > vhost_user_set_features: 130000000 > vhost_user_write req:2 flags:0x1 > vhost_user_write req:37 flags:0x9 > vhost_user_read_start > vhost_user_read req:37 flags:0x5 > vhost_user_write req:8 flags:0x1 > vhost_user_write req:10 flags:0x1 > vhost_user_write req:9 flags:0x1 > vhost_user_write req:12 flags:0x1 > vhost_user_write req:13 flags:0x1 > > albeit with a slightly different message sequence > (VHOST_USER_ADD_MEM_REG instead of VHOST_USER_SET_MEM_TABLE). Reading > the C code you can see why: > > need_reply = vmsg.flags & VHOST_USER_NEED_REPLY_MASK; > > reply_requested = vu_process_message(dev, &vmsg); > if (!reply_requested && need_reply) { > vmsg_set_reply_u64(&vmsg, 0); > reply_requested = 1; > } > > So regardless of what may have been negotiated it will always reply with > something if the master requested it do so. This points us at the > specification which reads: > > - Bit 3 is the need_reply flag - see :ref:`REPLY_ACK ` for > details. > > which says in VHOST_USER_PROTOCOL_F_REPLY_ACK that this bit should only > be honoured when the feature has been negotiated. Which brings us to a > series of questions: > > - Should QEMU have preserved VhostUserVirtioFeatures::PROTOCOL_FEATURES > when doing the eventual VHOST_USER_SET_FEATURES reply? > > - Is vhost.rs being to strict or libvhost-user too lax in interpreting > the negotiated features before processing the ``need_reply`` [Bit 3] > field of the messages? I think vhost.rs is being correctly strict - but there would be no harm in it flagging that you'd hit an inconsistency if it finds a need_reply without the feature. > - are VHOST_USER_SET_MEM_TABLE to VHOST_USER_SET_INFLIGHT_FD included > in the "list of the ones that do" require replies or do they only > reply when REPLY_ACK has been negotiated as the ambiguous "seealso::" > box out seems to imply? set_mem_table gives a reply when postcopy is enabled (and then qemu replies to the reply!) but otherwise doesn't. (Note there's an issue opened for .rs to support ADD_MEM_REGION since it's a lot better than SET_MEM_TABLE which has a fixed size table that's small). Dave > Currently I have some hacks in: > > https://github.com/stsquad/vhost/tree/my-hacks > > which gets my daemon booting up to the point we actually need to do a > transaction. However I won't submit a PR until I've worked out exactly > where the problems are. > > -- > Alex Bennée > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK