From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932095AbeAWUqA (ORCPT ); Tue, 23 Jan 2018 15:46:00 -0500 Received: from www.llwyncelyn.cymru ([82.70.14.225]:58816 "EHLO fuzix.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752568AbeAWUp7 (ORCPT ); Tue, 23 Jan 2018 15:45:59 -0500 Date: Tue, 23 Jan 2018 20:45:52 +0000 From: Alan Cox To: Andrew Cooper Cc: David Woodhouse , Subject: Re: [PATCH v2 5/5] x86/pti: Do not enable PTI on fixed Intel processors Message-ID: <20180123204552.14040f98@alans-desktop> In-Reply-To: References: <1516726375-25168-1-git-send-email-dwmw@amazon.co.uk> <1516726375-25168-6-git-send-email-dwmw@amazon.co.uk> <20180123173312.1d8cf02f@alans-desktop> Organization: Intel Corporation X-Mailer: Claws Mail 3.15.1-dirty (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > static int in_order_cpu(void) > > { > > /* Processors with CPU id etc */ > > if (x86_match_cpu(cpu_in_order)) > > return 1; > > /* Other rules here */ > > return 0; > > } > > Why does in-order vs out-of-order matter? > > There are leaky SP3 gadgets which satisfy in-order requirements, so long > as the processor is capable of speculating 3 instructions past an > unresolved branch. > > What would (at a guess) save an in-order speculative processor from > being vulnerable is if memory reads are issued and resolve in program > order, but in that case, it is not the in-order property of the > processor which makes it safe. Fair point - I should rename it cpu_speculates(). The atoms in that list don't speculate. Alan [My Cyrix 6x86 had a different kind of meltdown problem....]