Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758169AbaDXWpN (ORCPT ); Thu, 24 Apr 2014 18:45:13 -0400 Received: from mail-vc0-f169.google.com ([209.85.220.169]:59705 "EHLO mail-vc0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758991AbaDXWoI (ORCPT ); Thu, 24 Apr 2014 18:44:08 -0400 MIME-Version: 1.0 In-Reply-To: <53599225.7010407@zytor.com> References: <1398120472-6190-1-git-send-email-hpa@linux.intel.com> <53598F2F.1030306@linux.intel.com> <53599225.7010407@zytor.com> From: Andrew Lutomirski Date: Thu, 24 Apr 2014 15:43:47 -0700 Message-ID: Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE* To: "H. Peter Anvin" Cc: "H. Peter Anvin" , comex , Linux Kernel Mailing List , Linus Torvalds , Ingo Molnar , Alexander van Heukelum , Konrad Rzeszutek Wilk , Boris Ostrovsky , Borislav Petkov , 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 Thu, Apr 24, 2014 at 3:37 PM, H. Peter Anvin wrote: > On 04/24/2014 03:31 PM, Andrew Lutomirski wrote: >> >> I was imagining just randomizing a couple of high bits so the whole >> espfix area moves as a unit. >> >>> We could XOR with a random constant with no penalty at all. Only >>> problem is that this happens early, so the entropy system is not yet >>> available. Fine if we have RDRAND, but... >> >> How many people have SMAP and not RDRAND? I think this is a complete >> nonissue for non-SMAP systems. >> > > Most likely none, unless some "clever" virtualizer turns off RDRAND out > of spite. > >>>> Peter, is this idea completely nuts? The only exceptions that can >>>> happen there are NMI, MCE, #DB, #SS, and #GP. The first four use IST, >>>> so they won't double-fault. >>> >>> It is completely nuts, but sometimes completely nuts is actually useful. >>> It is more complexity, to be sure, but it doesn't seem completely out >>> of the realm of reason, and avoids having to unwind the ministack except >>> in the normally-fatal #DF handler. #DFs are documented as not >>> recoverable, but we might be able to do something here. >>> >>> The only real disadvantage I see is the need for more bookkeeping >>> metadata. Basically the bitmask in espfix_64.c now needs to turn into >>> an array, plus we need a second percpu variable. Given that if >>> CONFIG_NR_CPUS=8192 the array has 128 entries I think we can survive that. >> >> Doing something in #DF needs percpu data? What am I missing? > > You need the second percpu variable in the espfix setup code so you have > both the write address and the target rsp (read address). > Duh. :) --Andy -- 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/