From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932393AbWGRUqF (ORCPT ); Tue, 18 Jul 2006 16:46:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932395AbWGRUqF (ORCPT ); Tue, 18 Jul 2006 16:46:05 -0400 Received: from dsl027-180-168.sfo1.dsl.speakeasy.net ([216.27.180.168]:35812 "EHLO sunset.davemloft.net") by vger.kernel.org with ESMTP id S932393AbWGRUqE (ORCPT ); Tue, 18 Jul 2006 16:46:04 -0400 Date: Tue, 18 Jul 2006 13:46:25 -0700 (PDT) Message-Id: <20060718.134625.123974562.davem@davemloft.net> To: zach@vmware.com Cc: arjan@infradead.org, chrisw@sous-sol.org, linux-kernel@vger.kernel.org, virtualization@lists.osdl.org, xen-devel@lists.xensource.com, jeremy@goop.org, ak@suse.de, akpm@osdl.org, rusty@rustcorp.com.au, ian.pratt@xensource.com, Christian.Limpach@cl.cam.ac.uk Subject: Re: [RFC PATCH 18/33] Subarch support for CPUID instruction From: David Miller In-Reply-To: <44BCC720.7050601@vmware.com> References: <20060718091953.003336000@sous-sol.org> <1153217686.3038.37.camel@laptopd505.fenrus.org> <44BCC720.7050601@vmware.com> X-Mailer: Mew version 4.2 on Emacs 21.4 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: Zachary Amsden Date: Tue, 18 Jul 2006 04:33:52 -0700 > You really need a CPUID hook. The instruction is non-virtualizable, and > anything claiming to be a hypervisor really has to support masking and > flattening the cpuid namespace for the instruction itself. It is used > in assembler code and very early in boot. The alternative is injecting > a bunch of Xen-specific code to filter feature bits into the i386 layer, > which is both bad for Linux and bad for Xen - and was quite ugly in the > last set of Xen patches. Userspace will still see the full set of cpuid bits, since it can still execute cpuid unimpeded, is this ok?