From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH 2/2] Expose tsc deadline timer cpuid to guest Date: Thu, 05 Jan 2012 18:34:41 -0200 Message-ID: <4F060961.9050002@web.de> References: <4F0482D6.8080705@web.de> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig150B4368B99142EEF33353AA" Cc: "qemu-devel@nongnu.org" , Marcelo Tosatti , Avi Kivity , kvm , Alexey Zaytsev To: "Liu, Jinsong" Return-path: In-Reply-To: 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 2440 and 3156) --------------enig150B4368B99142EEF33353AA Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 2012-01-05 18:07, Liu, Jinsong wrote: >> Sorry, it remains bogus to expose the tsc deadline timer feature on >> machines < pc-1.1. That's just like we introduced kvmclock only to >> pc-0.14 onward. The reason is that guest OSes so far running on >> qemu-1.0 or older without deadline timer support must not find that >> feature when being migrated to a host with qemu-1.1 in pc-1.0 compat >> mode. Yes, the user can explicitly disable it, but that is not the >> idea of legacy machine models. They should provide the very same >> environment that older qemu versions offered. >> >=20 > Not quite clear about this point. > Per my understanding, if a kvm guest running on an older qemu without t= sc deadline timer support,=20 > then after migrate, the guest would still cannot find tsc deadline feat= ure, no matter older or newer host/qemu/pc-xx it migrate to. What should prevent this? The feature flags are not part of the vmstate. They are part of the vm configuration which is not migrated but defined by starting qemu on the target host. Jan --------------enig150B4368B99142EEF33353AA Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk8GCWUACgkQitSsb3rl5xQE6QCgwvZWG+fdQQUTy9drjpRKqc7l FSgAn08oIz6i6d0KSV3q+wx0Nha3fld9 =GS4a -----END PGP SIGNATURE----- --------------enig150B4368B99142EEF33353AA--