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 76674D116F1 for ; Mon, 1 Dec 2025 15:11:32 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vQ5Y1-0001Le-Vm; Mon, 01 Dec 2025 10:10:42 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vQ5Xy-0001Kp-Ql for qemu-devel@nongnu.org; Mon, 01 Dec 2025 10:10:39 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vQ5Xv-0008Kz-Sg for qemu-devel@nongnu.org; Mon, 01 Dec 2025 10:10:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1764601833; 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=a24pTb94oO+4rCYyg7J5OcMpbSrbQIpLE5O9Bsy3MkM=; b=UAQLMMo6qJO3PANANsVN6Sa6YstkIlTxcqs3k7guU+FIQU3e8nBEhnN8C8DE5j16J6ciGO 0iyLE3vmfjSxcCjRM/VABRsp8xgEfLxi0fbFsmzliFqGbEIjWnwIGMhaaX3CyNyuxLT5fm yXAP+PJnXhpn6iGroRf+aeW4Mv6PqyY= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-626-9zq78jZkN5G5OsH0pMOxsQ-1; Mon, 01 Dec 2025 10:10:24 -0500 X-MC-Unique: 9zq78jZkN5G5OsH0pMOxsQ-1 X-Mimecast-MFC-AGG-ID: 9zq78jZkN5G5OsH0pMOxsQ_1764601822 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 62410195609F; Mon, 1 Dec 2025 15:10:21 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.139]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 325D118004A3; Mon, 1 Dec 2025 15:10:17 +0000 (UTC) Date: Mon, 1 Dec 2025 15:10:14 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Chalios, Babis" Cc: "mst@redhat.com" , "imammedo@redhat.com" , "cohuck@redhat.com" , "pbonzini@redhat.com" , "qemu-devel@nongnu.org" , "dwmw2@infradead.org" , "Graf (AWS), Alexander" , "mzxreary@0pointer.de" Subject: Re: [RFC PATCH 0/4] vmclock: add support for VM generation counter and notifications Message-ID: References: <20251201125023.18344-1-bchalios@amazon.es> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20251201125023.18344-1-bchalios@amazon.es> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Dec 01, 2025 at 12:50:24PM +0000, Chalios, Babis wrote: > Latest specification of VMClock[1] adds support for VM generation counter > and notifications. VM generation counter is similar to disruption_marker > but it only changes when the guest has been loaded from a snapshot, not > on live migration. Its purpose is to notify the guest about snapshot > events and let it perform actions such as recreating UUIDs, resetting > network connections, reseeding entropy, etc. > > Moreover, the spec now describes a notification that the device can send > after updating the seq counter to a new even number. > > I have already sent the Linux changes to the mailing list here: > https://lore.kernel.org/lkml/20251127103159.19816-1-bchalios@amazon.es/T/#u > > [1] https://david.woodhou.se/VMClock.pdf Should that spec document the expected behaviour of guests when a hypervisor advertizes both vmclock and vmgenid devices ? QEMU supports both, and to avoid assumptions about whether a guest supports the newer vmclock, I could expect mgmt apps to expose both these QEMU devices. IIUC, your intent is that 'vmclock' obsoletes the need for 'vmgenid', so should the spec say that explicitly, and suggest that guest kernels ignore the vmgenid if both are present, to avoid the same kind of actions being triggered twice ? With 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 :|