From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: Nested kvm_intel broken on pre 3.3 hosts Date: Wed, 1 Aug 2012 16:39:40 +0300 Message-ID: <20120801133940.GB27579@redhat.com> References: <50191307.5030107@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, Avi Kivity , Andy Whitcroft To: Stefan Bader Return-path: Received: from mx1.redhat.com ([209.132.183.28]:48378 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752310Ab2HANjn (ORCPT ); Wed, 1 Aug 2012 09:39:43 -0400 Content-Disposition: inline In-Reply-To: <50191307.5030107@canonical.com> Sender: kvm-owner@vger.kernel.org List-ID: 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 turned 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 instead of > required? According to Intel SDM there was never CPU that didn't support RDPMC exiting. Looks like unfortunate nested VMX bug. > Seems also like kvm_amd does not "suffer" from any test that could fail and > should be ok (though I did not test it personally). > > -Stefan > > [1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1031090 > -- Gleb.