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 4827DD116F3 for ; Mon, 1 Dec 2025 15:24:12 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vQ5kx-0006Fk-Tl; Mon, 01 Dec 2025 10:24:03 -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 1vQ5kt-0006DX-Rw for qemu-devel@nongnu.org; Mon, 01 Dec 2025 10:23:59 -0500 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vQ5ks-0001SN-BU for qemu-devel@nongnu.org; Mon, 01 Dec 2025 10:23:59 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=To8av4PkogRS6v1Xr1+oXj10ut+9/eX7WWCg4wXaTeI=; b=CZYTYtQKANNimhFvR0LbVAJ8CY dqTwVcFiVQRMIw5gmH6jBB9tLZvZk3BPZfJdd5z9+Cn+OjbUC4+5rbnhpvN+UR12e85ZgP63RnvSQ yqsOAirJvsmIsRTOwosFNS5ums12DkckYmlBDY7T0/jcWevOb5ud7o1SrSnLTJiEFJzUaaXIXGzDS sernj2pZZwYvYFoSQ5r0LX0bB91Y2KB0WX0IN2irkVRke84cHGlOojzR2RqnyfrVhwmHlj/UOfRGn wEdLtzw/9KG1BjCq54UZC6lNk3WsY2Q/ZO2Y9LLY9LAvmUfbMvrtidCLCRIDz8ChO5xYf3LqZJsFi kerSYQ6Q==; Received: from [172.31.31.148] (helo=u09cd745991455d.lumleys.internal) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vQ4tA-0000000G5S8-1AOJ; Mon, 01 Dec 2025 14:28:33 +0000 Message-ID: <74932716b6165b5b69ecdca65c7668c622d8a257.camel@infradead.org> Subject: Re: [RFC PATCH 0/4] vmclock: add support for VM generation counter and notifications From: David Woodhouse To: "Daniel P." =?ISO-8859-1?Q?Berrang=E9?= , "Chalios, Babis" Cc: "mst@redhat.com" , "imammedo@redhat.com" , "cohuck@redhat.com" , "pbonzini@redhat.com" , "qemu-devel@nongnu.org" , "Graf (AWS), Alexander" , "mzxreary@0pointer.de" Date: Mon, 01 Dec 2025 15:23:48 +0000 In-Reply-To: References: <20251201125023.18344-1-bchalios@amazon.es> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-nOiHCC758IUoDzWUejYY" User-Agent: Evolution 3.52.3-0ubuntu1 MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html Received-SPF: none client-ip=2001:8b0:10b:1:d65d:64ff:fe57:4e05; envelope-from=BATV+cd717ce28a9accd739e3+8135+infradead.org+dwmw2@desiato.srs.infradead.org; helo=desiato.infradead.org X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_NONE=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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --=-nOiHCC758IUoDzWUejYY Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2025-12-01 at 15:10 +0000, Daniel P. Berrang=C3=A9 wrote: > On Mon, Dec 01, 2025 at 12:50:24PM +0000, Chalios, Babis wrote: > > Latest specification of VMClock[1] adds support for VM generation count= er > > and notifications. VM generation counter is similar to disruption_marke= r > > 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. > >=20 > > Moreover, the spec now describes a notification that the device can sen= d > > after updating the seq counter to a new even number. > >=20 > > 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 > >=20 > > [1] https://david.woodhou.se/VMClock.pdf >=20 > Should that spec document the expected behaviour of guests when a hypervi= sor > advertizes both vmclock and vmgenid devices ? >=20 > QEMU supports both, and to avoid assumptions about whether a guest suppor= ts > the newer vmclock, I could expect mgmt apps to expose both these QEMU > devices. >=20 > IIUC, your intent is that 'vmclock' obsoletes the need for 'vmgenid', so > should the spec say that explicitly, and suggest that guest kernels ignor= e > the vmgenid if both=C2=A0 are present, to avoid the same kind of actions = being > triggered twice ? The intent is not to obsolete vmgenid, but we do signal when a clock disruption is associated with a snapshot (and thus with a vmgenid change), and the conditions for bumping that counter (which is what you were reviewing) will be the same as the conditions for when to regenerate a new vmgenid UUID. --=-nOiHCC758IUoDzWUejYY Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj 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