From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 92E012D594A; Fri, 28 Nov 2025 12:36:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764333379; cv=none; b=em+VvXKN+ztrSQxoGuecR/oOEC7GtMlqwkyyKC9+ONQS1n+PcBEIAnk15X73alIhLZFikts7AkWN/jF4hsLgxCY7WlR8KOzXuTBIbgSR2tO+k4mvRIyK1UvjGpJeVn7KlXXuxh5mA1DKXJNR+oTkyBY7fYKVyXv+536vp1lvMBA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764333379; c=relaxed/simple; bh=l7+b4AsStFy3zNfTRUBVzjopnaMs9DsYO2r5728Qkrc=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=jz0u1Tw/nWNYIffZZ95QuEcH+T2/UeFNs7OAHGxmIXb/4B6faMUCatGUxCdB7Jvt/OKE6US7D4j+34oLCDaslGtPrI3kGB46xInkyy70PG7LdvYCARP3vIwz7P0ZYWhNiPRZOR2boUqySVtndRSJ822vNgNb1UPCXc3H6w3ri7Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=c+1k95FX; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="c+1k95FX" 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=Auc+3/kRjs/uqefAnhVAtJtJdhc34coltqwimMQyGlo=; b=c+1k95FXn5C6jC8Ouxy03lepHO oLWn+k8NUcFF3hq3sFlEu2HiPTAMMdKOuYt490Dm3g5W7o+6IZpT0v68z3inpJm2Rw9lFYmFOGqP+ TYxHUBw1wdF7sDqghjWfPki8+eCu6Bh21/aG85OJVJMflh/JjLsCmXLFsgJUd1+LhvTo3HbxrvhN3 x6eibkDFw70BJsaLAlWqaBdKDrBd5imQhs2FAjH73YoU3XNDgRKz1yqB2ePak+M0+nHcGUITgI3MG YXs2LmOJRoKaSl9Rj2Tp5WmDmK1Vr2AUmx2OVAsHXjM74+KOcLyQt7J3vbIIAmbjLIiJvXwk1LUw3 08og6xtQ==; 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 1vOwqC-0000000BtsY-3QaC; Fri, 28 Nov 2025 11:40:45 +0000 Message-ID: Subject: Re: [PATCH 1/2] ptp: vmclock: add vm generation counter From: David Woodhouse To: "Chalios, Babis" , "richardcochran@gmail.com" , "andrew+netdev@lunn.ch" , "davem@davemloft.net" , "edumazet@google.com" , "kuba@kernel.org" , "pabeni@redhat.com" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" Cc: "Graf (AWS), Alexander" , "mzxreary@0pointer.de" Date: Fri, 28 Nov 2025 12:36:06 +0000 In-Reply-To: <20251127103159.19816-2-bchalios@amazon.es> References: <20251127103159.19816-1-bchalios@amazon.es> <20251127103159.19816-2-bchalios@amazon.es> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-aaXC1lgYozcTliT4fBAQ" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-aaXC1lgYozcTliT4fBAQ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2025-11-27 at 10:32 +0000, Chalios, Babis wrote: > Similar to live migration, loading a VM from some saved state (aka > snapshot) is also an event that calls for clock adjustments in the > guest. However, guests might want to take more actions as a response to > such events, e.g. as discarding UUIDs, resetting network connections, > reseeding entropy pools, etc. These are actions that guests don't > typically take during live migration, so add a new field in the > vmclock_abi called vm_generation_counter which informs the guest about > such events. >=20 > Hypervisor advertises support for vm_generation_counter through the > VMCLOCK_FLAG_VM_GEN_COUNTER_PRESENT flag. Users need to check the > presence of this bit in vmclock_abi flags field before using this flag. >=20 > Signed-off-by: Babis Chalios Reviewed-by: David Woodhouse We are writing up a formal definition of the VMClock device which includes these updates, and I believe the QEMU patches are to follow. I've put an early draft at https://david.woodhou.se/VMClock.pdf > --- > =C2=A0include/uapi/linux/vmclock-abi.h | 15 +++++++++++++++ > =C2=A01 file changed, 15 insertions(+) >=20 > diff --git a/include/uapi/linux/vmclock-abi.h b/include/uapi/linux/vmcloc= k-abi.h > index 2d99b29ac44a..937fe00e4f33 100644 > --- a/include/uapi/linux/vmclock-abi.h > +++ b/include/uapi/linux/vmclock-abi.h > @@ -115,6 +115,12 @@ struct vmclock_abi { > =C2=A0 * bit again after the update, using the about-to-be-valid fields. > =C2=A0 */ > =C2=A0#define VMCLOCK_FLAG_TIME_MONOTONIC (1 << 7) > + /* > + * If the VM_GEN_COUNTER_PRESENT flag is set, the hypervisor will > + * bump the vm_generation_counter field every time the guest is > + * loaded from some save state (restored from a snapshot). > + */ > +#define VMCLOCK_FLAG_VM_GEN_COUNTER_PRESENT=C2=A0=C2=A0=C2=A0=C2=A0 (1 <= < 8) > =C2=A0 > =C2=A0 __u8 pad[2]; > =C2=A0 __u8 clock_status; > @@ -177,6 +183,15 @@ struct vmclock_abi { > =C2=A0 __le64 time_frac_sec; /* Units of 1/2^64 of a second */ > =C2=A0 __le64 time_esterror_nanosec; > =C2=A0 __le64 time_maxerror_nanosec; > + > + /* > + * This field changes to another non-repeating value when the guest > + * has been loaded from a snapshot. In addition to handling a > + * disruption in time (which will also be signalled through the > + * disruption_marker field), a guest may wish to discard UUIDs, > + * reset network connections, reseed entropy, etc. > + */ > + __le64 vm_generation_counter; > =C2=A0}; > =C2=A0 > =C2=A0#endif /*=C2=A0 __VMCLOCK_ABI_H__ */ --=-aaXC1lgYozcTliT4fBAQ 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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