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=-18.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, 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 C8D58C433DB for ; Tue, 9 Feb 2021 03:46:30 +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 4465C64EAA for ; Tue, 9 Feb 2021 03:46:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4465C64EAA 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]:57162 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l9Jyv-0001p9-3f for qemu-devel@archiver.kernel.org; Mon, 08 Feb 2021 22:46:29 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:39712) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l9Jxo-0001O3-W8 for qemu-devel@nongnu.org; Mon, 08 Feb 2021 22:45:21 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:46644) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l9Jxl-0003LV-Dx for qemu-devel@nongnu.org; Mon, 08 Feb 2021 22:45:20 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612842316; 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=xBTf3FjFdUMeawaxUiFXlKO+Je85xoDu7QaLiU7M1YM=; b=XcU86XI2hRRp8QnhskPTlp34uGxI3snve4V6mOehLZYB8sEKQiRSuDaZXzgU/Mc+VPlUKc zP2+hcJOGvl+K31OCkVWqA1STyluRCgsJQMbaKNKKgehC7JwpIKv+gABx8lqfT4b5sKaHh yDVp3FlI1EEvlMyEy6IUmZQNdFsaf4U= 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-518-7WSaeBfYNg-7LgEjyj9HUA-1; Mon, 08 Feb 2021 22:45:14 -0500 X-MC-Unique: 7WSaeBfYNg-7LgEjyj9HUA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BDE2285B6C1; Tue, 9 Feb 2021 03:45:13 +0000 (UTC) Received: from [10.72.13.32] (ovpn-13-32.pek2.redhat.com [10.72.13.32]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5C5D35D734; Tue, 9 Feb 2021 03:45:04 +0000 (UTC) Subject: Re: [PATCH 3/3] virtio-net: graceful fallback to vhost=off for tap netdev To: Yuri Benditovich References: <20210204202915.15925-1-yuri.benditovich@daynix.com> <20210204202915.15925-4-yuri.benditovich@daynix.com> <1f0f901c-8ad0-60a4-383f-851fc0f093ff@redhat.com> From: Jason Wang Message-ID: Date: Tue, 9 Feb 2021 11:45:03 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=63.128.21.124; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.57, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.265, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=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: Yan Vugenfirer , qemu-devel@nongnu.org, "Michael S . Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2021/2/9 上午3:59, Yuri Benditovich wrote: > On Mon, Feb 8, 2021 at 6:11 AM Jason Wang wrote: >> >> On 2021/2/5 上午4:29, Yuri Benditovich wrote: >>> Currently virtio-net silently clears features if they are >>> not supported by respective vhost. This may create migration >>> problems in future if vhost features on the source and destination >>> are different. Implement graceful fallback to no-vhost mode >>> when some acked features contradict with vhost. The decision is >>> taken on set_features call and the vhost will be disabled >>> till next reset (or migration). >>> Such fallback is currently enabled only for TAP netdev. >>> >>> Signed-off-by: Yuri Benditovich >>> --- >>> hw/net/virtio-net.c | 58 ++++++++++++++++++++++++++++++++++++++------- >>> 1 file changed, 50 insertions(+), 8 deletions(-) >>> >>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c >>> index 5150f295e8..b353060e63 100644 >>> --- a/hw/net/virtio-net.c >>> +++ b/hw/net/virtio-net.c >>> @@ -515,6 +515,15 @@ static RxFilterInfo *virtio_net_query_rxfilter(NetClientState *nc) >>> return info; >>> } >>> >>> +static void virtio_net_allow_vhost(VirtIONet *n, bool allow) >>> +{ >>> + int i; >>> + for (i = 0; i < n->max_queues; i++) { >>> + NetClientState *nc = qemu_get_subqueue(n->nic, i)->peer; >>> + nc->vhost_net_disabled = !allow; >>> + } >>> +} >>> + >>> static void virtio_net_reset(VirtIODevice *vdev) >>> { >>> VirtIONet *n = VIRTIO_NET(vdev); >>> @@ -552,6 +561,7 @@ static void virtio_net_reset(VirtIODevice *vdev) >>> assert(!virtio_net_get_subqueue(nc)->async_tx.elem); >>> } >>> } >>> + virtio_net_allow_vhost(n, true); >>> } >>> >>> static void peer_test_vnet_hdr(VirtIONet *n) >>> @@ -689,6 +699,15 @@ static void virtio_net_set_queues(VirtIONet *n) >>> } >>> } >>> >>> +static bool can_disable_vhost(VirtIONet *n) >>> +{ >>> + NetClientState *peer = qemu_get_queue(n->nic)->peer; >>> + if (!get_vhost_net(peer)) { >>> + return false; >>> + } >>> + return !peer || peer->info->type == NET_CLIENT_DRIVER_TAP; >>> +} >>> + >>> static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue); >>> >>> static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features, >>> @@ -725,14 +744,14 @@ static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features, >>> return features; >>> } >>> >>> - virtio_clear_feature(&features, VIRTIO_NET_F_RSS); >>> - virtio_clear_feature(&features, VIRTIO_NET_F_HASH_REPORT); >>> - features = vhost_net_get_features(get_vhost_net(nc->peer), features); >>> - vdev->backend_features = features; >>> + vdev->backend_features = vhost_net_get_features(get_vhost_net(nc->peer), features); >>> >>> - if (n->mtu_bypass_backend && >>> - (n->host_features & 1ULL << VIRTIO_NET_F_MTU)) { >>> - features |= (1ULL << VIRTIO_NET_F_MTU); >>> + if (!can_disable_vhost(n)) { >>> + features = vdev->backend_features; >>> + if (n->mtu_bypass_backend && >>> + (n->host_features & 1ULL << VIRTIO_NET_F_MTU)) { >>> + features |= (1ULL << VIRTIO_NET_F_MTU); >>> + } >>> } >>> >>> return features; >>> @@ -872,10 +891,25 @@ static void failover_add_primary(VirtIONet *n, Error **errp) >>> error_propagate(errp, err); >>> } >>> >>> +static bool check_vhost_features(VirtIONet *n, uint64_t features) >>> +{ >>> + NetClientState *nc = qemu_get_queue(n->nic); >>> + uint64_t filtered; >>> + if (n->rss_data.redirect) { >>> + return false; >>> + } >>> + filtered = vhost_net_get_features(get_vhost_net(nc->peer), features); >>> + if (filtered != features) { >>> + return false; >>> + } >>> + return true; >>> +} >>> + >>> static void virtio_net_set_features(VirtIODevice *vdev, uint64_t features) >>> { >>> VirtIONet *n = VIRTIO_NET(vdev); >>> Error *err = NULL; >>> + bool disable_vhost = false; >>> int i; >>> >>> if (n->mtu_bypass_backend && >>> @@ -894,13 +928,21 @@ static void virtio_net_set_features(VirtIODevice *vdev, uint64_t features) >>> VIRTIO_F_VERSION_1), >>> virtio_has_feature(features, >>> VIRTIO_NET_F_HASH_REPORT)); >>> - >>> n->rsc4_enabled = virtio_has_feature(features, VIRTIO_NET_F_RSC_EXT) && >>> virtio_has_feature(features, VIRTIO_NET_F_GUEST_TSO4); >>> n->rsc6_enabled = virtio_has_feature(features, VIRTIO_NET_F_RSC_EXT) && >>> virtio_has_feature(features, VIRTIO_NET_F_GUEST_TSO6); >>> n->rss_data.redirect = virtio_has_feature(features, VIRTIO_NET_F_RSS); >>> >>> + if (can_disable_vhost(n)) { >>> + disable_vhost = !check_vhost_features(n, features); >>> + } >>> + if (disable_vhost) { >>> + warn_report("Some of requested features aren't supported by vhost, " >>> + "vhost is turned off till next reset"); >>> + virtio_net_allow_vhost(n, false); >>> + } >> >> This looks more complicated than I expected. See >> virtio_net_vhost_status() we had a fallback there: >> >> r = vhost_net_start(vdev, n->nic->ncs, queues); >> if (r < 0) { >> error_report("unable to start vhost net: %d: " >> "falling back on userspace virtio", -r); >> n->vhost_started = 0; >> } >> >> I wonder if we can simply depends on this (which is proved to be work >> for the past years) by not clearing dev->acked_features like: >> >> if (!can_disable_vhost(n)) { >> features = vhost_net_get_features(get_vhost_net(nc->peer), features); >> } else { >> vdev->backend_features = features; >> } >> >> Then we probably don't need other tricks. > Of course we can. > But I would prefer to make things more clear, i.e. make > get_vhost_net() always return a meaningful result, even (as an > example) in procedures called from set_feature() after the > vhost_disabled is set. > Otherwise people can rely on get_vhost_net() and call its methods > which potentially can do something that we do not expect. > In some places in the code (also in future) we'll need to check not > only get_vhost_net() but also is_vhost_disabled. IMO, not too elegant, > but possible. I see. > Of course, being a decision maker, you can request to do it simpler > and do not maintain a consistent result of get_vhost_net(). > But then please tell it explicitly. So the reason that I prefer the above simple checks is that we've already had two falling backs points in virtio_net_vhost_status(): 1) for vnet_hdr_swap:         if (n->needs_vnet_hdr_swap) {             error_report("backend does not support %s vnet headers; "                          "falling back on userspace virtio",                          virtio_is_big_endian(vdev) ? "BE" : "LE");             return;         } 2) for all of the other cases:         n->vhost_started = 1;         r = vhost_net_start(vdev, n->nic->ncs, queues);         if (r < 0) {             error_report("unable to start vhost net: %d: "                          "falling back on userspace virtio", -r);             n->vhost_started = 0;         } So it's better to have a consistent way: 1) Introduce the variable disable_vhost as you suggest or 2) falling back by checking the return status of vhost_net_start() In this case, 2) looks much more easier than convert all the falling backs to 1). Thanks > >> Thanks >> >> >>> + >>> if (n->has_vnet_hdr) { >>> n->curr_guest_offloads = >>> virtio_net_guest_offloads_by_features(features);