From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= Subject: PVH cpuid feature flags Date: Tue, 21 Jan 2014 20:28:14 +0100 Message-ID: <52DECA4E.4080004@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Konrad Rzeszutek Wilk , Mukesh Rathor , xen-devel List-Id: xen-devel@lists.xenproject.org Hello, While doing some benchmarks on PV/PVH/PVHVM, I've realized that the cpuid feature flags exposed to PVH guests are kind of strange, this is the output of the feature flags as seen by an HVM domain: Features=0x1783fbff Features2=0x81b82201 AMD Features=0x28100800 AMD Features2=0x1 And this is what a PVH domain sees when running on the same hardware: Features=0x1fc98b75 Features2=0x80982201 AMD Features=0x20100800 AMD Features2=0x1 I would expect the feature flags to be quite similar between an HVM domain and a PV domain (since they both run inside of a HVM container). AFAIK, there's no reason to disable PSE, PGE, PSE36 and RDTSCP for PVH guests. Also, is there any reason why PVH guests have the ACPI, SS and CLFLUSH feature flags but not HVM? Most (if not all) of this probably comes from the fact that we are reporting the same feature flags as pure PV guests, but I see no reason to do that for PVH guests, we should decide what's supported on PVH and set the feature flags accordingly. Roger.