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,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 7ACD9C433F5 for ; Wed, 8 Sep 2021 13:51:07 +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 1AF3560EBA for ; Wed, 8 Sep 2021 13:51:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 1AF3560EBA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:37454 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mNxyk-0007mo-1C for qemu-devel@archiver.kernel.org; Wed, 08 Sep 2021 09:51:06 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35984) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mNxx9-0006fY-8g for qemu-devel@nongnu.org; Wed, 08 Sep 2021 09:49:27 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:42856) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mNxx6-0005r1-H9 for qemu-devel@nongnu.org; Wed, 08 Sep 2021 09:49:26 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631108963; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=RioyZBHZIZVXNvYL83wqB8ZPB6VXojQAXaT68GaSPqU=; b=acmE2sqNV2vD55TcS2NlcZpo0wuipqT/pUg+ErT8UsBQ4qCpeZmKsJpSCdR6C0jnOXMC27 dzh41uGcFlAhejZ47jQUeOpet6ymCcb0RVrU0TQAuwjswSgZSpgUaMT+esFIHAGLgrc+7t CR8KyjgpumJbT4y4e0GaMObc7pOdgF8= 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-478-o0ofT4qHNYGSul8bXNxHoQ-1; Wed, 08 Sep 2021 09:49:18 -0400 X-MC-Unique: o0ofT4qHNYGSul8bXNxHoQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0E478108E6EC; Wed, 8 Sep 2021 13:48:52 +0000 (UTC) Received: from redhat.com (unknown [10.39.192.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B1F2D1A26A; Wed, 8 Sep 2021 13:48:49 +0000 (UTC) Date: Wed, 8 Sep 2021 14:48:47 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Stefano Garzarella Subject: Re: [PATCH] vhost-vsock: fix migration issue when seqpacket is supported Message-ID: References: <20210907124935.147164-1-sgarzare@redhat.com> <20210907134756.apnxzgbvw2ztetag@steredhat> <20210908134135.xvidtghamwahbdqk@steredhat> MIME-Version: 1.0 In-Reply-To: <20210908134135.xvidtghamwahbdqk@steredhat> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 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 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.393, 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_H2=-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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Eduardo Habkost , Jiang Wang , "Michael S. Tsirkin" , Jason Wang , qemu-stable@nongnu.org, qemu-devel@nongnu.org, Stefan Hajnoczi , Arseny Krasnov Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Sep 08, 2021 at 03:41:35PM +0200, Stefano Garzarella wrote: > On Tue, Sep 07, 2021 at 03:47:56PM +0200, Stefano Garzarella wrote: > > On Tue, Sep 07, 2021 at 02:22:24PM +0100, Daniel P. Berrangé wrote: > > > On Tue, Sep 07, 2021 at 02:49:35PM +0200, Stefano Garzarella wrote: > > > > Commit 1e08fd0a46 ("vhost-vsock: SOCK_SEQPACKET feature bit support") > > > > enabled the SEQPACKET feature bit. > > > > This commit is released with QEMU 6.1, so if we try to migrate a VM where > > > > the host kernel supports SEQPACKET but machine type version is less than > > > > 6.1, we get the following errors: > > > > > > > > Features 0x130000002 unsupported. Allowed features: 0x179000000 > > > > Failed to load virtio-vhost_vsock:virtio > > > > error while loading state for instance 0x0 of device '0000:00:05.0/virtio-vhost_vsock' > > > > load of migration failed: Operation not permitted > > > > > > > > Let's disable the feature bit for machine types < 6.1, adding a > > > > `features` field to VHostVSock to simplify the handling of upcoming > > > > features we will support. > > > > > > IIUC, this will still leave migration broken for anyone migrating > > > a >= 6.1 machine type between a kernel that supports SEQPACKET and > > > a kernel lacking that, or vica-verca. > > > > This should be true for migrating from kernel that supports SEQPACKET to > > a kernel lacking that. > > > > For vice-versa I'm not sure, since vhost_get_features() will disable > > that feature if the host kernel doesn't support it, and the guest will > > not have acked it. > > I did some testing and the migration is only broken in the case of > kernel 5.14+ (SEQPACKET supported) -> kernel 5.13 (SEQPACKET not supported). > > Vice-versa works well because the feature is not acked. > > > > > > > > > If a feature is dependant on a host kernel feature we can't turn > > > that on automatically as part of the machine type, as we need > > > ABI stability across migration indepdant of kernel version. > > > > > > > How do we typically handle this? > > > > I wrongly thought it was an expected behavior that migrating a guest > > using a vhost device from a new kernel to an old one can fail if not all > > features are supported. > > > > I need to take a look at the other vhost devices. > > I took a look at vhost-net and vhost-scsi and we don't seem to handle this > case. Maybe I'm missing something... We've never done very well at having a consistent story wrt deps on kernel features. So I wouldn't be surprised to see differences or omissions anywhere and people not notice the issue. > So following your advice, the best thing would be to have this feature > disabled by default and require the user to enable it explicitly so we are > sure it is needed. At this point a migration to a kernel that doesn't > support it is rightly broken. > > Or is there something better we can do? > > @Michael @Jason any thoughts? 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 :|