From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Blake Subject: Re: [PATCH v13 1/8] save/load cpu runstate Date: Fri, 01 Mar 2013 09:29:20 -0700 Message-ID: <5130D760.70908@redhat.com> References: <512FC845.9080209@redhat.com> <20130301073648.GD16362@localhost.localdomain> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="----enig2IQQMSOUPJIDWITKASEXF" Cc: Peter Maydell , Gleb Natapov , "Michael S. Tsirkin" , Jan Kiszka , qemu-devel , Markus Armbruster , Blue Swirl , Orit Wasserman , kvm list , Juan Quintela , Alexander Graf , Andrew Jones , Alex Williamson , Sasha Levin , Stefan Hajnoczi , Luiz Capitulino , KAMEZAWA Hiroyuki , Kevin Wolf , Anthony Liguori , Marcelo Tosatti , "linux-kernel@vger.kernel.org" , Paolo Bonzini To: Hu Tao Return-path: In-Reply-To: <20130301073648.GD16362@localhost.localdomain> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org Sender: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org List-Id: kvm.vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) ------enig2IQQMSOUPJIDWITKASEXF Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 03/01/2013 12:36 AM, Hu Tao wrote: > On Thu, Feb 28, 2013 at 02:12:37PM -0700, Eric Blake wrote: >> On 02/28/2013 05:13 AM, Hu Tao wrote: >>> This patch enables preservation of cpu runstate during save/load vm. >>> So when a vm is restored from snapshot, the cpu runstate is restored,= >>> too. >> >> What happens if a management app wants to override the runstate when >> restoring the domain? I can think of several useful scenarios: >> >> 1. management app pauses the guest, then saves domain state and other >> things (management state, or disk clones), then resumes the guest. >> Later, the management wants to revert to the saved state, but have the= >> guest running right away. I guess here, knowing that the guest was >> saved in a paused state doesn't hurt, since the management app can >> resume it right away. >> >> 2. management app saves domain state of a live guest, then copies that= >> state elsewhere. In its new location, the management app wants to >> investigate the state for forensic analysis - so even though the guest= >> remembers that it was running, management wants to start it paused. >> Here, it is important that there must not be a window of time where th= e >> guest can run, otherwise, the results are not reproducible. >=20 > -S takes precedence in the case. But for in-migration, runstate is > loaded from src. Given your answer, I think we're okay from the libvirt perspective. My biggest worry about a window where the guest runs unchecked is not a problem, given that libvirt always uses -S on incoming migration. In turn, libvirt has its own mechanisms for tracking whether the outgoing migration was started from a running state, along with API overrides to let a user override whether libvirt will resume the guest on the incoming migration side. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org ------enig2IQQMSOUPJIDWITKASEXF Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.13 (GNU/Linux) Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJRMNdgAAoJEKeha0olJ0Nq0kEH/1SbK8p7fVUNjgKkqfpK8gb1 x/VQR88hsWDEeYO9wzaWjUIlS081QVm39kcGyeuYQFqtKA3ixUvIIuEDbtyzOS37 IQWQpwU0C/ILluJrQaqEFD77HwJAMi86SNVuQA2KvYOYXZrJIzKn5Q5ads1vDnPy pCv9nbwmu2kWc1rcXa9MPXqYq1yowsW5AWW0VM3m8tFIgc8VJbiSH/Ulku7KpzEu u0Xqun7tKOsF29l5TxMWwDPuSi/iPTovwpngz00VPQiMt5vrgj0rhA7Uj7xlWxyW DDT7Lf8OLlGbLEBsDAMDz0uwV5gZjl0ewaa5WIfGq+sYlfu0Lt1mzE+Ovq7R9r0= =F9rp -----END PGP SIGNATURE----- ------enig2IQQMSOUPJIDWITKASEXF--