Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753421AbWKCSGI (ORCPT ); Fri, 3 Nov 2006 13:06:08 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753423AbWKCSGI (ORCPT ); Fri, 3 Nov 2006 13:06:08 -0500 Received: from mailout1.vmware.com ([65.113.40.130]:24967 "EHLO mailout1.vmware.com") by vger.kernel.org with ESMTP id S1753421AbWKCSGF (ORCPT ); Fri, 3 Nov 2006 13:06:05 -0500 Message-ID: <454B850C.3050402@vmware.com> Date: Fri, 03 Nov 2006 10:06:04 -0800 From: Zachary Amsden User-Agent: Thunderbird 1.5.0.7 (X11/20060909) MIME-Version: 1.0 To: Chuck Ebbert <76306.1226@compuserve.com> Cc: linux-kernel , Linus Torvalds , Andrew Morton , Andi Kleen Subject: Re: [patch] i386: remove IOPL check on task switch References: <200611030130_MC3-1-D02A-DEB@compuserve.com> In-Reply-To: <200611030130_MC3-1-D02A-DEB@compuserve.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1316 Lines: 38 Chuck Ebbert wrote: > IOPL is implicitly saved and restored on task switch, > so explicit check is no longer needed. > > Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com> > > --- 2.6.19-rc4-32smp.orig/arch/i386/kernel/process.c > +++ 2.6.19-rc4-32smp/arch/i386/kernel/process.c > @@ -681,12 +681,6 @@ struct task_struct fastcall * __switch_t > loadsegment(gs, next->gs); > > /* > - * Restore IOPL if needed. > - */ > - if (unlikely(prev->iopl != next->iopl)) > - set_iopl_mask(next->iopl); > - > - /* > * Now maybe handle debug registers and/or IO bitmaps > */ > if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW) > Nack. This is used for paravirt-ops kernels that use IOPL'd userspace. Fixing it would require a fairly heavy penalty on the iret path, since every single instruction there contributes to a critical region which must have custom fixup code, or some other technique to provide protection against interrupt re-entrancy. At least, let's discuss other potential solutions first - for now it is harmless. Zach - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/