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Tsirkin" To: Eli Cohen Subject: Re: VIRTIO_NET_F_MTU not negotiated Message-ID: <20220728024257-mutt-send-email-mst@kernel.org> References: <20220727032334-mutt-send-email-mst@kernel.org> <20220727053311-mutt-send-email-mst@kernel.org> <20220727114228-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: Eugenio Perez Martin , "qemu-devel@nongnu.org" , "virtualization@lists.linux-foundation.org" X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Thu, Jul 28, 2022 at 05:51:32AM +0000, Eli Cohen wrote: > > From: Michael S. Tsirkin > > Sent: Wednesday, July 27, 2022 6:44 PM > > To: Eli Cohen > > Cc: Eugenio Perez Martin ; qemu-devel@nongnu.org; Jason Wang ; > > virtualization@lists.linux-foundation.org > > Subject: Re: VIRTIO_NET_F_MTU not negotiated > > > > On Wed, Jul 27, 2022 at 10:16:19AM +0000, Eli Cohen wrote: > > > > -----Original Message----- > > > > From: Michael S. Tsirkin > > > > Sent: Wednesday, July 27, 2022 12:35 PM > > > > To: Eli Cohen > > > > Cc: Eugenio Perez Martin ; qemu-devel@nongnu.org; Jason Wang ; > > > > virtualization@lists.linux-foundation.org > > > > Subject: Re: VIRTIO_NET_F_MTU not negotiated > > > > > > > > On Wed, Jul 27, 2022 at 09:04:47AM +0000, Eli Cohen wrote: > > > > > > -----Original Message----- > > > > > > From: Michael S. Tsirkin > > > > > > Sent: Wednesday, July 27, 2022 10:25 AM > > > > > > To: Eli Cohen > > > > > > Cc: Eugenio Perez Martin ; qemu-devel@nongnu.org; Jason Wang ; > > > > > > virtualization@lists.linux-foundation.org > > > > > > Subject: Re: VIRTIO_NET_F_MTU not negotiated > > > > > > > > > > > > On Wed, Jul 27, 2022 at 06:51:56AM +0000, Eli Cohen wrote: > > > > > > > I found out that the reason why I could not enforce the mtu stems from the fact that I did not configure max mtu for the net > > > > device > > > > > > (e.g. through libvirt ). > > > > > > > Libvirt does not allow this configuration for vdpa devices and probably for a reason. The vdpa backend driver has the > > freedom > > > > to do > > > > > > it using its copy of virtio_net_config. > > > > > > > > > > > > > > The code in qemu that is responsible to allow to consider the device MTU restriction is here: > > > > > > > > > > > > > > static void virtio_net_device_realize(DeviceState *dev, Error **errp) > > > > > > > { > > > > > > > VirtIODevice *vdev = VIRTIO_DEVICE(dev); > > > > > > > VirtIONet *n = VIRTIO_NET(dev); > > > > > > > NetClientState *nc; > > > > > > > int i; > > > > > > > > > > > > > > if (n->net_conf.mtu) { > > > > > > > n->host_features |= (1ULL << VIRTIO_NET_F_MTU); > > > > > > > } > > > > > > > > > > > > > > The above code can be interpreted as follows: > > > > > > > if the command line arguments of qemu indicates that mtu should be limited, then we would read this mtu limitation from > > the > > > > > > device (that actual value is ignored). > > > > > > > > > > > > > > I worked around this limitation by unconditionally setting VIRTIO_NET_F_MTU in the host features. As said, it only indicates > > > > that > > > > > > we should read the actual limitation for the device. > > > > > > > > > > > > > > If this makes sense I can send a patch to fix this. > > > > > > > > > > > > Well it will then either have to be for vdpa only, or have > > > > > > compat machinery to avoid breaking migration. > > > > > > > > > > > > > > > > How about this one: > > > > > > > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > > > > index 1067e72b3975..e464e4645c79 100644 > > > > > --- a/hw/net/virtio-net.c > > > > > +++ b/hw/net/virtio-net.c > > > > > @@ -3188,6 +3188,7 @@ static void virtio_net_guest_notifier_mask(VirtIODevice *vdev, int idx, > > > > > static void virtio_net_set_config_size(VirtIONet *n, uint64_t host_features) > > > > > { > > > > > virtio_add_feature(&host_features, VIRTIO_NET_F_MAC); > > > > > + virtio_add_feature(&host_features, VIRTIO_NET_F_MTU); > > > > > > > > > > n->config_size = virtio_feature_get_config_size(feature_sizes, > > > > > host_features); > > > > > > > > Seems to increase config size unconditionally? > > > > > > Right but you pay for reading two more bytes. Is that such a high price to pay? > > > > > > That's not a performance question. The issue compatibility, size > > should not change for a given machine type. > > > > Did you mean it should not change for virtio_net pci devices? yes > Can't management controlling the live migration process take care of this? Management does what it always did which is set flags consistently. If we tweak them with virtio_add_feature it can do nothing. > > > > > > > > > > > @@ -3512,6 +3513,7 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp) > > > > > > > > > > if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) { > > > > > struct virtio_net_config netcfg = {}; > > > > > + n->host_features |= (1ULL << VIRTIO_NET_F_MTU); > > > > > memcpy(&netcfg.mac, &n->nic_conf.macaddr, ETH_ALEN); > > > > > vhost_net_set_config(get_vhost_net(nc->peer), > > > > > (uint8_t *)&netcfg, 0, ETH_ALEN, VHOST_SET_CONFIG_TYPE_MASTER); > > > > > > > > And the point is vdpa does not support migration anyway ATM, right? > > > > > > > > > > I don't see how this can affect vdpa live migration. Am I missing something? > > > > config size affects things like pci BAR size. This must not change > > during migration. > > > > Why should this change during live migration? Simply put features need to match on both ends. > > -- > > MST _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization 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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 3A8A2C04A68 for ; Thu, 28 Jul 2022 07:05:13 +0000 (UTC) Received: from localhost ([::1]:41694 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oGxa4-0008C6-50 for qemu-devel@archiver.kernel.org; Thu, 28 Jul 2022 03:05:12 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59916) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oGxI5-0001VD-93 for qemu-devel@nongnu.org; Thu, 28 Jul 2022 02:46:37 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:52835) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oGxI2-0003am-0Y for qemu-devel@nongnu.org; Thu, 28 Jul 2022 02:46:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1658990793; 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: in-reply-to:in-reply-to:references:references; bh=VVlg4ZDriIr9yuhH+5AZkqioVyHgUvTYzgVgHD7Vooc=; b=edQSydGwGJctTjBYRCFyAqpM6MTkqtQjmdK3wdGX9WCbMCdjNBDQMEhYTdg8XrSpK1IHvb HH2cQ+3QlvesUuGybEGd3i9zIIBaYsv78DDqLNNDwSS3Vusrh26hM8B5WMGKLqLggfAE07 IQMpqGHrES91wfAsSqddJp6kKa4aaQY= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-627-0m72YrXrO5-9zXEytwC_Jg-1; Thu, 28 Jul 2022 02:46:31 -0400 X-MC-Unique: 0m72YrXrO5-9zXEytwC_Jg-1 Received: by mail-wm1-f72.google.com with SMTP id r82-20020a1c4455000000b003a300020352so550293wma.5 for ; Wed, 27 Jul 2022 23:46:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc; bh=VVlg4ZDriIr9yuhH+5AZkqioVyHgUvTYzgVgHD7Vooc=; b=V0ZUf7XTk/l0mqIWjI9+6aQQAUJihwvcJ0zT25o9DP8sskzqmopb8joFOEB4qWrFqn gaHfN3bIwFRU/34MS+P3jmMoUCK8iUkYmd00Ecx/zOFwvO6MuwE7Jrw/T41TkyT9vhBz gF8uyYK7RAPZaxfS1wiYVSpTRhPOWv4wNMPeBZ4dRyp3y1gkzMkrv/Qsm5KLTyeb99Kx JLzOAtDXLn0Yth2OSv0Sb10wNAFxt2AEwoH+QZpEt2XQxaop1Z6FojxST79UR9+F7AKw Dz6sXOQ9pbiu9Kui3tY2wq9Iwi7QZJSDyGl+KDXO/07toUwxF39DUgvV12PNpdCsLzui /YRA== X-Gm-Message-State: AJIora+5/+uXzAxP3g53WZl3UIRhkaQrYTKNJ0lz0A1JaHpryy/sxJF9 JpchJNvRrjUVsYnaJtivZIFfN+TSJ5oIQWti2UwWBYNSx1UeUNvfowXaYiplsYjxYcBEI+E0qIh fEtWpSDtI+Si9tTU= X-Received: by 2002:a7b:c3d4:0:b0:3a3:ce7:7894 with SMTP id t20-20020a7bc3d4000000b003a30ce77894mr5479718wmj.134.1658990790283; Wed, 27 Jul 2022 23:46:30 -0700 (PDT) X-Google-Smtp-Source: AGRyM1umYkl91s09bq48tXOKYt8gpsMeqKv8QU/I6YvWaUcJ/Vx0RJ4Y0ujyN1l+orJ7RczikeRhjw== X-Received: by 2002:a7b:c3d4:0:b0:3a3:ce7:7894 with SMTP id t20-20020a7bc3d4000000b003a30ce77894mr5479696wmj.134.1658990789752; Wed, 27 Jul 2022 23:46:29 -0700 (PDT) Received: from redhat.com ([2.54.183.236]) by smtp.gmail.com with ESMTPSA id d10-20020adfe84a000000b0021e4982270asm73798wrn.13.2022.07.27.23.46.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Jul 2022 23:46:29 -0700 (PDT) Date: Thu, 28 Jul 2022 02:46:24 -0400 From: "Michael S. Tsirkin" To: Eli Cohen Cc: Eugenio Perez Martin , "qemu-devel@nongnu.org" , Jason Wang , "virtualization@lists.linux-foundation.org" Subject: Re: VIRTIO_NET_F_MTU not negotiated Message-ID: <20220728024257-mutt-send-email-mst@kernel.org> References: <20220727032334-mutt-send-email-mst@kernel.org> <20220727053311-mutt-send-email-mst@kernel.org> <20220727114228-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jul 28, 2022 at 05:51:32AM +0000, Eli Cohen wrote: > > From: Michael S. Tsirkin > > Sent: Wednesday, July 27, 2022 6:44 PM > > To: Eli Cohen > > Cc: Eugenio Perez Martin ; qemu-devel@nongnu.org; Jason Wang ; > > virtualization@lists.linux-foundation.org > > Subject: Re: VIRTIO_NET_F_MTU not negotiated > > > > On Wed, Jul 27, 2022 at 10:16:19AM +0000, Eli Cohen wrote: > > > > -----Original Message----- > > > > From: Michael S. Tsirkin > > > > Sent: Wednesday, July 27, 2022 12:35 PM > > > > To: Eli Cohen > > > > Cc: Eugenio Perez Martin ; qemu-devel@nongnu.org; Jason Wang ; > > > > virtualization@lists.linux-foundation.org > > > > Subject: Re: VIRTIO_NET_F_MTU not negotiated > > > > > > > > On Wed, Jul 27, 2022 at 09:04:47AM +0000, Eli Cohen wrote: > > > > > > -----Original Message----- > > > > > > From: Michael S. Tsirkin > > > > > > Sent: Wednesday, July 27, 2022 10:25 AM > > > > > > To: Eli Cohen > > > > > > Cc: Eugenio Perez Martin ; qemu-devel@nongnu.org; Jason Wang ; > > > > > > virtualization@lists.linux-foundation.org > > > > > > Subject: Re: VIRTIO_NET_F_MTU not negotiated > > > > > > > > > > > > On Wed, Jul 27, 2022 at 06:51:56AM +0000, Eli Cohen wrote: > > > > > > > I found out that the reason why I could not enforce the mtu stems from the fact that I did not configure max mtu for the net > > > > device > > > > > > (e.g. through libvirt ). > > > > > > > Libvirt does not allow this configuration for vdpa devices and probably for a reason. The vdpa backend driver has the > > freedom > > > > to do > > > > > > it using its copy of virtio_net_config. > > > > > > > > > > > > > > The code in qemu that is responsible to allow to consider the device MTU restriction is here: > > > > > > > > > > > > > > static void virtio_net_device_realize(DeviceState *dev, Error **errp) > > > > > > > { > > > > > > > VirtIODevice *vdev = VIRTIO_DEVICE(dev); > > > > > > > VirtIONet *n = VIRTIO_NET(dev); > > > > > > > NetClientState *nc; > > > > > > > int i; > > > > > > > > > > > > > > if (n->net_conf.mtu) { > > > > > > > n->host_features |= (1ULL << VIRTIO_NET_F_MTU); > > > > > > > } > > > > > > > > > > > > > > The above code can be interpreted as follows: > > > > > > > if the command line arguments of qemu indicates that mtu should be limited, then we would read this mtu limitation from > > the > > > > > > device (that actual value is ignored). > > > > > > > > > > > > > > I worked around this limitation by unconditionally setting VIRTIO_NET_F_MTU in the host features. As said, it only indicates > > > > that > > > > > > we should read the actual limitation for the device. > > > > > > > > > > > > > > If this makes sense I can send a patch to fix this. > > > > > > > > > > > > Well it will then either have to be for vdpa only, or have > > > > > > compat machinery to avoid breaking migration. > > > > > > > > > > > > > > > > How about this one: > > > > > > > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > > > > index 1067e72b3975..e464e4645c79 100644 > > > > > --- a/hw/net/virtio-net.c > > > > > +++ b/hw/net/virtio-net.c > > > > > @@ -3188,6 +3188,7 @@ static void virtio_net_guest_notifier_mask(VirtIODevice *vdev, int idx, > > > > > static void virtio_net_set_config_size(VirtIONet *n, uint64_t host_features) > > > > > { > > > > > virtio_add_feature(&host_features, VIRTIO_NET_F_MAC); > > > > > + virtio_add_feature(&host_features, VIRTIO_NET_F_MTU); > > > > > > > > > > n->config_size = virtio_feature_get_config_size(feature_sizes, > > > > > host_features); > > > > > > > > Seems to increase config size unconditionally? > > > > > > Right but you pay for reading two more bytes. Is that such a high price to pay? > > > > > > That's not a performance question. The issue compatibility, size > > should not change for a given machine type. > > > > Did you mean it should not change for virtio_net pci devices? yes > Can't management controlling the live migration process take care of this? Management does what it always did which is set flags consistently. If we tweak them with virtio_add_feature it can do nothing. > > > > > > > > > > > @@ -3512,6 +3513,7 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp) > > > > > > > > > > if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) { > > > > > struct virtio_net_config netcfg = {}; > > > > > + n->host_features |= (1ULL << VIRTIO_NET_F_MTU); > > > > > memcpy(&netcfg.mac, &n->nic_conf.macaddr, ETH_ALEN); > > > > > vhost_net_set_config(get_vhost_net(nc->peer), > > > > > (uint8_t *)&netcfg, 0, ETH_ALEN, VHOST_SET_CONFIG_TYPE_MASTER); > > > > > > > > And the point is vdpa does not support migration anyway ATM, right? > > > > > > > > > > I don't see how this can affect vdpa live migration. Am I missing something? > > > > config size affects things like pci BAR size. This must not change > > during migration. > > > > Why should this change during live migration? Simply put features need to match on both ends. > > -- > > MST