Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933414AbaDVRTs (ORCPT ); Tue, 22 Apr 2014 13:19:48 -0400 Received: from mail-vc0-f182.google.com ([209.85.220.182]:46192 "EHLO mail-vc0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932199AbaDVRTq (ORCPT ); Tue, 22 Apr 2014 13:19:46 -0400 MIME-Version: 1.0 In-Reply-To: References: <5355A9E9.9070102@zytor.com> <1dbe8155-58da-45c2-9dc0-d9f4b5a6e643@email.android.com> <20140422112312.GB15882@pd.tnic> <20140422144659.GF15882@pd.tnic> <53569467.1030809@zytor.com> Date: Tue, 22 Apr 2014 10:19:46 -0700 X-Google-Sender-Auth: 6QeLscCDh6qtega55ULfSpzCWMk Message-ID: Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE* From: Linus Torvalds To: Andrew Lutomirski Cc: "H. Peter Anvin" , Borislav Petkov , "H. Peter Anvin" , Linux Kernel Mailing List , Ingo Molnar , Alexander van Heukelum , Konrad Rzeszutek Wilk , Boris Ostrovsky , Arjan van de Ven , Brian Gerst , Alexandre Julliard , Andi Kleen , Thomas Gleixner Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 22, 2014 at 10:11 AM, Andrew Lutomirski wrote: > >> >> Anyway, if done correctly, this whole espfix should be totally free >> for normal processes, since it should only trigger if SS is a LDT >> entry (bit #2 set in the segment descriptor). So the normal fast-path >> should just have a simple test for that. > > How? Doesn't something still need to check whether SS is funny before > doing iret? Just test bit #2. Don't do anything else if it's clear, because you should be done. You don't need to do anything special if it's clear, because I don't *think* we have any 16-bit data segments in the GDT on x86-64. Linus -- 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/