From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752975AbaEBVok (ORCPT ); Fri, 2 May 2014 17:44:40 -0400 Received: from mga03.intel.com ([143.182.124.21]:39719 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752765AbaEBVoj (ORCPT ); Fri, 2 May 2014 17:44:39 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,974,1389772800"; d="scan'208";a="426964582" Message-ID: <536411C1.4040209@intel.com> Date: Fri, 02 May 2014 14:44:33 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Andy Lutomirski CC: Linus Torvalds , Thomas Gleixner , Linux Kernel Mailing List , the arch/x86 maintainers , Steven Rostedt , Gleb Natapov , Paolo Bonzini Subject: Re: [RFC/HACK] x86: Fast return to kernel References: <210a076ea197ae384705d2c02cfff12a951a62f8.1399057218.git.luto@amacapital.net> <53641035.4040202@intel.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/02/2014 02:42 PM, Andy Lutomirski wrote: > > Hah -- I think I just faked both of you out :) > > I don't think this has anything to do with the error code, and I think > that the errorentry code already does more or less that: it pushes -1. > > The real issue here is probably the magic 16-byte stack alignment when > a non-stack-switching interrupt happens. > Errorentry is when there *is* an error code pushed by the hardware. The other variant is zeroentry, which does generate a zero error code -- eventually. The -1 means we didn't enter the kernel through a system call. -hpa