From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: Xen HVM regression on certain Intel CPUs Date: Wed, 27 Mar 2013 20:24:58 +0000 Message-ID: References: <5153222B.3030605@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5153222B.3030605@canonical.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Stefan Bader , Konrad Rzeszutek Wilk Cc: wei.y.yang@intel.com, "xen-devel@lists.xensource.com" , haitao.shan@intel.com, xin.li@intel.com, "H. Peter Anvin" List-Id: xen-devel@lists.xenproject.org On 27/03/2013 16:45, "Stefan Bader" wrote: >>> Seems that I was relying on the wrong source of information when checking >>> SMEP >>> support. The cpuid command seems at fail. But /proc/cpuinfo reports it. So >>> that >>> at least explains where that comes from... sorry for that. >> >> OK, so if you boot Xen with smep=1 (which disables SMEP, kind of >> counterintuive flag) >> that would work fine? > > Rebooting with smep=1 as a hv argument does not fix it. But I would be careful > since I just quickly did this without checking whether Xen 4.2.1 undestands > the > flag already. Yes, the flag is understood by all Xen 4.2 releases. However it is not inverted as you believe: it really is smep=0 or smep=off or even no-smep to disable SMEP. smep=1 will enable SMEP (which is the default anyway). I also checked how CPUID.SMEP gets set for an HVM guest, and it is very obviously masked off if SMEP support has been disabled or is unavailable. So I do not think we can be erroneously passing the CPUID flag to the guest. -- Keir