From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765389AbYETKFS (ORCPT ); Tue, 20 May 2008 06:05:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1765531AbYETKBa (ORCPT ); Tue, 20 May 2008 06:01:30 -0400 Received: from one.firstfloor.org ([213.235.205.2]:35980 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1765648AbYETKB2 (ORCPT ); Tue, 20 May 2008 06:01:28 -0400 Message-ID: <4832A173.6020203@firstfloor.org> Date: Tue, 20 May 2008 12:01:23 +0200 From: Andi Kleen User-Agent: Thunderbird 1.5.0.12 (X11/20060911) MIME-Version: 1.0 To: Suresh Siddha CC: Mikael Pettersson , mingo@elte.hu, hpa@zytor.com, tglx@linutronix.de, torvalds@linux-foundation.org, akpm@linux-foundation.org, roland@redhat.com, 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> In-Reply-To: <20080520015723.GD30034@linux-os.sc.intel.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Suresh Siddha wrote: > On Mon, May 19, 2008 at 04:52:01PM +0200, Mikael Pettersson wrote: >>> But we can >>> use some what similar magic, if the fxsave/fxrstor give away >>> some of the fields at the end of fxsave image (today it is reserved >>> and ignored during fxsave/fxrstor) for software use. >>> We can then use these fields at the end of fpstate, to indicate the presence of >>> xstate. But this requires some architecture changes like giving >>> away this space for SW use. We can take this to architects and >>> see what they think. >> If the HW doesn't store anything valuable there, we could store >> SW flags/cookies there on signal delivery, and clear them before >> fxrstor (unless the HW is known to ignore those fields). >> But it depends on how forgiving the HW is. > > Ok. CPU folks are planning to make some of the bytes at the end of fxsave > image, SW usable. Are they always zeroed in earlier CPUs though? If not that wouldn't work 100% reliably because whatever cookie you put in could have been there before by chance. I don't see anything in the SDM guaranteeing zeroing. -Andi