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=-5.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 BE674C433DB for ; Tue, 9 Feb 2021 14:53:32 +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 3AFC864E9C for ; Tue, 9 Feb 2021 14:53:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3AFC864E9C 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]:37498 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l9UOR-0006xp-7w for qemu-devel@archiver.kernel.org; Tue, 09 Feb 2021 09:53:31 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:56346) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l9UMP-000452-2H for qemu-devel@nongnu.org; Tue, 09 Feb 2021 09:51:25 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:60640) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l9UMK-0004wa-C7 for qemu-devel@nongnu.org; Tue, 09 Feb 2021 09:51:24 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612882277; h=from:from:reply-to: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=hdnaq/RfX8NNYdWi1HE45nvRzF938LCti9KQAyhIyOo=; b=PrbJDkVHs0dWtqlW64NpylWC3h7ijv3m7g1gu5j2KxYBPNAOge2Ol1TuVbQ4usloMuX64C tri/bVsuAF9sBkZuR8KQrvYM5oL9mUb23PBsFuejdm2R7DJ3KxDgGrHEyXJAjd/FJsQX+4 /32jY4E7YU6jXyPihmoZSueyWCGo70M= 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-370-hte23L7UP3uTUpVvXrFewA-1; Tue, 09 Feb 2021 09:51:13 -0500 X-MC-Unique: hte23L7UP3uTUpVvXrFewA-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 DDF326D4E0; Tue, 9 Feb 2021 14:51:12 +0000 (UTC) Received: from redhat.com (ovpn-115-66.ams2.redhat.com [10.36.115.66]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 76B8070471; Tue, 9 Feb 2021 14:51:08 +0000 (UTC) Date: Tue, 9 Feb 2021 14:51:05 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Michael S. Tsirkin" Subject: Re: [PATCH 0/3] virtio-net: graceful drop of vhost for TAP Message-ID: <20210209145105.GP1166421@redhat.com> References: <20210204202915.15925-1-yuri.benditovich@daynix.com> <20210209093201-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: <20210209093201-mutt-send-email-mst@kernel.org> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 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, RCVD_IN_DNSWL_LOW=-0.7, 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: yan@daynix.com, Yuri Benditovich , jasowang@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Feb 09, 2021 at 09:34:20AM -0500, Michael S. Tsirkin wrote: > On Thu, Feb 04, 2021 at 10:29:12PM +0200, Yuri Benditovich wrote: > > This set of patches introduces graceful switch from tap-vhost to > > tap-no-vhost depending on guest features. Before that the features > > that vhost does not support were silently cleared in get_features. > > This creates potential problem of migration from the machine where > > some of virtio-net features are supported by the vhost kernel to the > > machine where they are not supported (packed ring as an example). > > I still worry that adding new features will silently disable vhost for people. > Can we limit the change to when a VM is migrated in? Some management applications expect bi-directional live migration to work, so taking specific actions on incoming migration only feels dangerous. IMHO if the features we're adding cannot be expected to exist in host kernels in general, then the feature should defualt to off and require explicit user config to enable. Downstream distros which can guarantee newer kernels can flip the default in their custom machine types if they desire. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|