From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH 1/4] Fix tboot enabled macro Date: Wed, 26 May 2010 12:39:43 +0200 Message-ID: <4BFCFA6F.8030000@siemens.com> References: <4BFC9686.9050300@redhat.com> <4BFCCCFD.20203@web.de> <4BFCDDFB.9010505@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Avi Kivity , Zachary Amsden , kvm , Gleb Natapov To: "Wang, Shane" Return-path: Received: from thoth.sbs.de ([192.35.17.2]:15099 "EHLO thoth.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750727Ab0EZKj7 (ORCPT ); Wed, 26 May 2010 06:39:59 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: Wang, Shane wrote: > Avi Kivity wrote: >> On 05/26/2010 10:25 AM, Jan Kiszka wrote: >>> This is for CONFIG_INTEL_TXT enabled? Good point but needs to be >>> solved differently. tboot, the variable that is checked by the >>> original header, is not exported to modules. I wonder how this >>> worked out for you... >>> >>> Solution should be: hack tboot_enabled to kvm_tboot_enabled and >>> unconditionally define that to 0 for older kernels. If tboot is >>> actually enabled in hardware, KVM may not load but I'm unsure if >>> it's OK to assume tboot == 1 for that case or if that will cause >>> breakages if it's off instead - CC'ing the KVM patch author. >>> >> Worst case it doesn't load. I don't think it's a problem since >> enabling tboot will be rare for older kernels. > > tboot is not 0 if tboot module is run before kernel. > If "tboot is enabled in hardware" (I assume you mean if Intel TXT is enabled in hardware) > but tboot module is not run or old kernels don't support tboot module, > we still have outside_smx bit in feature msr. Why might KVM not load? If we have to hard-wire tboot_enabled in kvm-kmod to 0, KVM may not test all required bits and erroneously assume VTX would be disabled. So I wondered what would happen if we hard-wired it to 1, pretending that the tboot modules is loaded. Would we gain something without loosing on some other end? If not, I would simply leave things as they are now (i.e. always assuming tboot absence). Thanks, Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux