From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Bader Subject: Re: Nested kvm_intel broken on pre 3.3 hosts Date: Wed, 01 Aug 2012 16:26:28 +0200 Message-ID: <50193C94.1030809@canonical.com> References: <50191307.5030107@canonical.com> <20120801133940.GB27579@redhat.com> <50193875.3090200@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="------------enigA338D9C66E76E6D6104FCD8C" Cc: Gleb Natapov , kvm@vger.kernel.org, Andy Whitcroft To: Avi Kivity Return-path: Received: from youngberry.canonical.com ([91.189.89.112]:33134 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752421Ab2HAO0e (ORCPT ); Wed, 1 Aug 2012 10:26:34 -0400 In-Reply-To: <50193875.3090200@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigA338D9C66E76E6D6104FCD8C Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 01.08.2012 16:08, Avi Kivity wrote: > On 08/01/2012 04:39 PM, Gleb Natapov wrote: >> On Wed, Aug 01, 2012 at 01:29:11PM +0200, Stefan Bader wrote: >>> I have been looking at a report[1] about the kvm_intel module failing= to load on >>> linux v3.3 and newer guests when running on a v3.2 host. Bisection tu= rned up the >>> following patch: >>> >>> commit fee84b079d5ddee2247b5c1f53162c330c622902 >>> Author: Avi Kivity >>> Date: Thu Nov 10 14:57:25 2011 +0200 >>> >>> KVM: VMX: Intercept RDPMC >>> >>> Intercept RDPMC and forward it to the PMU emulation code. >>> >>> Signed-off-by: Avi Kivity >>> Signed-off-by: Gleb Natapov >>> Signed-off-by: Avi Kivity >>> >>> It looks like requiring the feature based on cpu fails when the host = (outer kvm >>> module) code does not support it. So maybe that should be optional in= stead of >>> required? >> According to Intel SDM there was never CPU that didn't support RDPMC >> exiting. Looks like unfortunate nested VMX bug. >=20 > Moreover, that same commit fixes the bug in nested vmx. So if you > update your host kernel to the same version as your L1 guest (or, at > your option, any later version) it should work. >=20 > We could backport that part of the patch, though as nested vmx is still= > experimential, I don't think it's worth it. >=20 Though this is probably what people will (or will have to) do. The host i= s not always under your control. Even with it being experimental, it was workin= g (at least the module was loadable) before and is now broken on Intel hosts. But ok, so the recommendation is to rather backport support to the host k= ernel than to try handling this differently in the guest module, right? --------------enigA338D9C66E76E6D6104FCD8C Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQIcBAEBCgAGBQJQGTyUAAoJEOhnXe7L7s6j4CcP/A7rr6pEjf2uG13dOl8VOJ0j 1qTeFcQ1W8scnDGjointjK3wQej6ruBU/b2iOuMcpNEeMiQTKZ9BiiD/0m1chpfj 9BvNNyUDFx8pGJqv47hE2TTOtSJ8XzAoTvLFXKMmraA6n9oMjhyB1ORZE/dVai3e 37P4fJtjS1bJiTjjirojwGJdH/RTCu8JBgQQCpcsww2mlZBT4hTnnqG+dDJC/lEh wCc0enurJVMsiil4IiLGYboR0rcZqv/+b/IsOlcxSdq8QOkyCeH0HaN6yOlxgTVh HFMpPyTpjtJTv2BwV8tYqci41TxEdNG3rQq7iCtjH2Tfee4+aBPAh7Eji0Uoa1mr AI9zsdF6D53rZNk2tJDWi0TUFNQ2KcvA7hECI6fsTyri6ZlJCPQeCXzUK8g49Eyz zdPl1bDyOaBU+EgzDXBIjudzWcwA71RmN5ahTcVpM2cCXVrs+fInJzMbDy7IrPMf RUdGdYPlNNHSfdzOURwCuAnfOg9NWXxYZNcfUBS77XgY+0GlOiIoPNpeiFfBKta+ tqFOCzX/NgFgMaytzuHU8PFT5CLg3E7jb7CGKd3jSQDbEzMN8HHsY3O6k+nicUC0 KYiRIRVusxNBE/8VzEM15C6e5Are/c9S0MnVV8XGiC/KsuwOScsNbsfY1w6w3m+x Qz3YBOVOjiU8hOd15TPo =GJvq -----END PGP SIGNATURE----- --------------enigA338D9C66E76E6D6104FCD8C--