From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 49B1649AA48 for ; Wed, 23 Sep 2026 15:28:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790177333; cv=none; b=XvjRmB4ZGpKTIL9XIuV175OcKAfSycJoDnxe1xg0QQf6KXinmSG07QdA1skf8LhdIqUeYhwgyacvDPDB3IunOTE3SWEmFYbksSAGiVLLZt3XTBS+Two5ccJdjL0e81pb720Wbcw0stKjFH3If3yDp5H9UoL+Ctad0gLst65PGww= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790177333; c=relaxed/simple; bh=dwSYJ2AvO5Gx873R19R5kywo6fBcLTcuPMkb5vEl6KQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=nq0goTlOUCV6avapw2pXXhMriI5WPf7T+b2Qptl+1PxJKkHkBZt/34ojVPDPi0t3EWbOJpAJLidHbbPsm/WRtFZtl0rj36zC7+Ym+yalnGE70dm1y8/0DAP68NvudyWBbB0hbnreS1y+2MAVDcuinmNlyARBa6WSVCQmiilzfGE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=emt7Nk//; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="emt7Nk//" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF7741F000FF; Wed, 23 Sep 2026 15:28:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790177326; bh=xWi+OqwCZfD7+DuS6d5A9ZOvKWrI1GDbMxsuaweXNMA=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=emt7Nk//V1Zs8cg1K1dDwhwXwgl6tQ/yJ0VN5ZLraIQ/qWs88Mi8N1QaLw9VMFuSn kfmd2Yz+/3AJVA3/74VvHtNSvgoezRWrG4Yhpd8K+erqixpnoHYt1tw4KMkFXyaeTh o4aoqVLFQ2Rei/3mbXUCgY3cWhOpaUuO93H1XQMXgCIFXsHtjrQyjDQhiQQaD/fbgr DZ21PpsnQKu8sQT8wpDnGqCj8gBeTFWO/hf2v0wK1Lxz9+SwLxBS2Qv1Ya2AYqc7qo Eo6ZNMbwdwarX30FlsrvYnWeo8lIeiuUk/cPwiThfs5+TIQTU7X87x0YJtAD4Z/LpI xJYH4PqNn0cTA== Date: Wed, 23 Sep 2026 10:28:38 -0500 From: "Serge Hallyn (AMD)" To: Artem Bityutskiy Cc: Peter Xu , Tony Lindgren , Paolo Bonzini , Sean Christopherson , Fabiano Rosas , Jon Grimm , Pankaj Gupta , Tom Lendacky , Marc Zyngier , Oliver Upton , Steven Price , Anup Patel , Samuel Ortiz , Jakub =?utf-8?B?UsWvxb5pxI1rYQ==?= , =?iso-8859-1?Q?J=F6rg_R=F6del?= , Vishal Annapurve , Elena Reshetova , Kai Huang , Kishen Maloor , Mika Westerberg , Peter Fang , Rick Edgecombe , Xiaoyao Li , Xu Yilun , kvm@vger.kernel.org Subject: Re: [RFC PATCH v2 0/4] Add KVM API for confidential guest live migration Message-ID: References: <20260831071304.762939-1-tony.lindgren@linux.intel.com> <84bf61e0e810859ed735dc92ab94167727c2e560.camel@gmail.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Sep 22, 2026 at 11:09:42AM +0300, Artem Bityutskiy wrote: > Hi Peter, ... > > Said that, we'll need to be careful then in case of migration fallbacks at > > the final stage. Nowadays, I believe QEMU can still fallback to source side > > at a very, very late stage after all things applied. If I'm not mistaken, > > the final handshake is done at migration_incoming_state_destroy() -> > > migrate_send_rp_shut() telling source to be gone. > > Right. In traditional pre-copy VM migration model, the fallback is possible > at any point before the destination VM starts running and modifying its > state. > > The same is true for TDX, but with more complexity and limitations. > > We have 2 points: > 1. Before the source has exported the start token - fallback is similar to > traditional VM migration - just abort the migration on source and > continue running the source TD, and just destroy the destination TD. > 2. After the source has exported the start token - fallback is still > possible, but more complex - it requires the destination to first > generate the abort token, which should be delivered to the source and > consumed there. There are seamcalls for both generating and consuming the > abort token. The token basically makes sure the destination cannot run, > and the source can run again - same "only one of the TDs can run at a > time" security rule that we discussed earlier. > > Now, the limitation here is that if the abort is because the network > connectivity is lost, the abort token cannot be delivered. Then I'd guess > migration should stop, without destroying the source and the destination, > and the token should be delivered later manually, QEMU could even provide an > infrastructure / commands for that. > > Would be very helpful to learn the abort protocol the other CoCo vendors > offer - is it similar to TDX or not? Yup, that sounds very similar to the expected SEV-SNP late abort semantics, -serge