From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH][uq/master] kvm: x86: Save/restore FPU OP, IP and DP Date: Tue, 14 Jun 2011 10:28:07 +0200 Message-ID: <4DF71B97.2030908@web.de> References: <4DF33413.9070605@web.de> <4DF5CE2E.50008@redhat.com> <4DF6FB62.60705@web.de> <4DF71A97.8090407@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigED88E17E8E79E8AF21B3795F" Cc: Marcelo Tosatti , kvm , qemu-devel , Stefan Hajnoczi , Christophe Fergeau To: Avi Kivity Return-path: Received: from fmmailgate02.web.de ([217.72.192.227]:56686 "EHLO fmmailgate02.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752645Ab1FNI2O (ORCPT ); Tue, 14 Jun 2011 04:28:14 -0400 In-Reply-To: <4DF71A97.8090407@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigED88E17E8E79E8AF21B3795F Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable On 2011-06-14 10:23, Avi Kivity wrote: > On 06/14/2011 09:10 AM, Jan Kiszka wrote: >> On 2011-06-13 10:45, Avi Kivity wrote: >> > On 06/11/2011 12:23 PM, Jan Kiszka wrote: >> >> From: Jan Kiszka >> >> >> >> These FPU states are properly maintained by KVM but not yet by >> TCG. So >> >> far we unconditionally set them to 0 in the guest which may cause >> >> state corruptions - not only during migration. >> >> >> >> >> >> -#define CPU_SAVE_VERSION 12 >> >> +#define CPU_SAVE_VERSION 13 >> >> >> > >> > Incrementing the version number seems excessive - I can't imagine a= >> > real-life guest will break due to fp pointer corruption >> > >> > However, I don't think we have a mechanism for optional state. We >> > discussed this during the 18th VMState Subsection Symposium and IIR= C >> > agreed to re-raise the issue when we encountered it, which appears >> to be >> > now. >> > >> >> Whatever we invent, it has to be backported as well to allow that >> infamous traveling back in time, migrating VMs from newer to older >> versions. >> >> Would that backporting be simpler if we used an unconditional subsecti= on >> for the additional states? >=20 > Most likely. It depends on what mechanism we use. >=20 > Let's spend some time to think about what it would be like. This patch= > is not urgent, is it? (i.e. it was discovered by code inspection, not > live migration that caught the cpu between an instruction that caused a= > math exception and the exception handler). Right, not urgent, should just make it into 0.15 in the end. Jan --------------enigED88E17E8E79E8AF21B3795F Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.15 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org/ iEYEARECAAYFAk33G5sACgkQitSsb3rl5xS0PgCfRWVxMFAZX+C0QuLJwRSwKooR 5VwAnjzU9kP2vkhLkimj2o0cfsyLwu2A =c68x -----END PGP SIGNATURE----- --------------enigED88E17E8E79E8AF21B3795F--