From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nadav Har'El Subject: Re: Nested kvm_intel broken on pre 3.3 hosts Date: Wed, 1 Aug 2012 18:07:07 +0300 Message-ID: <20120801150707.GA3688@fermat.math.technion.ac.il> References: <50191307.5030107@canonical.com> <20120801133940.GB27579@redhat.com> <50193875.3090200@redhat.com> <50193C94.1030809@canonical.com> <50193D3E.9090100@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Stefan Bader , Gleb Natapov , kvm@vger.kernel.org, Andy Whitcroft To: Avi Kivity Return-path: Received: from mailgw13.technion.ac.il ([132.68.225.13]:51997 "EHLO mailgw13.technion.ac.il" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755155Ab2HAPHP (ORCPT ); Wed, 1 Aug 2012 11:07:15 -0400 Content-Disposition: inline In-Reply-To: <50193D3E.9090100@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Aug 01, 2012, Avi Kivity wrote about "Re: Nested kvm_intel broken on pre 3.3 hosts": > Right - it's not just kvm-as-a-guest that will trip on this. But > there's no point in everyone backporting it on their own. If you're > doing the backport, please post it here and we'll forward it to the > stable branch. If I understand correctly, the failure occurs because new versions of KVM refuse to work if the processor doesn't support CPU_BASED_RDPMC_EXITING - which older versions of nested VMX didn't say that they did. But must the KVM guest refuse to work if this feature isn't supported? I.e., why not move in setup_vmcs_config() the CPU_BASED_RDPMC_EXITING from "min" to "opt"? Isn't losing the PMU feature a lesser evil than not working at all? In any case, perhaps the original reporter can use this as a workaround, at least, because it requires modifying the (L1) guest, not the host. -- Nadav Har'El | Wednesday, Aug 1 2012, 13 Av 5772 nyh@math.technion.ac.il |----------------------------------------- Phone +972-523-790466, ICQ 13349191 |May you live as long as you want - and http://nadav.harel.org.il |never want as long as you live.