From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933211AbYEVBqp (ORCPT ); Wed, 21 May 2008 21:46:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755733AbYEVBqh (ORCPT ); Wed, 21 May 2008 21:46:37 -0400 Received: from terminus.zytor.com ([198.137.202.10]:52119 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755268AbYEVBqh (ORCPT ); Wed, 21 May 2008 21:46:37 -0400 Message-ID: <4834CE97.9080708@zytor.com> Date: Wed, 21 May 2008 18:38:31 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Roland McGrath CC: Suresh Siddha , Mikael Pettersson , Andi Kleen , mingo@elte.hu, tglx@linutronix.de, torvalds@linux-foundation.org, akpm@linux-foundation.org, drepper@redhat.com, Hongjiu.lu@intel.com, linux-kernel@vger.kernel.org, arjan@linux.intel.com, rmk+lkml@arm.linux.org.uk, dan@debian.org, asit.k.mallick@intel.com Subject: Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions References: <20080513011030.GA31448@linux-os.sc.intel.com> <18477.35703.679574.760417@harpo.it.uu.se> <20080518013416.GB30034@linux-os.sc.intel.com> <18481.37905.297556.288317@harpo.it.uu.se> <20080520015723.GD30034@linux-os.sc.intel.com> <4832A173.6020203@firstfloor.org> <18482.53246.642835.894623@harpo.it.uu.se> <4832E705.2010900@zytor.com> <18482.60491.764019.292031@harpo.it.uu.se> <20080520175325.GE30034@linux-os.sc.intel.com> <4834BE39.2000904@zytor.com> <20080522005345.B994F26FA24@magilla.localdomain> In-Reply-To: <20080522005345.B994F26FA24@magilla.localdomain> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Roland McGrath wrote: >> The biggest potential problem with this that I see is that relying on >> CPUID can mess with certain virtualization solutions. Another option to >> accomplish the same thing would be to have a system call (preferrably a >> prctl, since it is at least in theory personality-dependent) to query >> what information is included in the fpstate data - since it will always >> be the same for any particular kernel. > > It's easy and cheap to add an indicator to the vDSO for this. Yes, but I suspect for legacy apps running without vDSO might matter. -hpa