Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754391AbbGWUx6 (ORCPT ); Thu, 23 Jul 2015 16:53:58 -0400 Received: from mail-la0-f51.google.com ([209.85.215.51]:36832 "EHLO mail-la0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753635AbbGWUxz (ORCPT ); Thu, 23 Jul 2015 16:53:55 -0400 MIME-Version: 1.0 In-Reply-To: <20150723205207.GA3052@1wt.eu> References: <20150723205207.GA3052@1wt.eu> From: Andy Lutomirski Date: Thu, 23 Jul 2015 13:53:34 -0700 Message-ID: Subject: Re: Dealing with the NMI mess To: Willy Tarreau Cc: Linus Torvalds , X86 ML , "linux-kernel@vger.kernel.org" , Borislav Petkov , Thomas Gleixner , Peter Zijlstra , Steven Rostedt , Brian Gerst Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1388 Lines: 33 On Thu, Jul 23, 2015 at 1:52 PM, Willy Tarreau wrote: > On Thu, Jul 23, 2015 at 01:38:33PM -0700, Linus Torvalds wrote: >> On Thu, Jul 23, 2015 at 1:21 PM, Andy Lutomirski wrote: >> > >> > 2. Forbid IRET inside NMIs. Doable but maybe not that pretty. >> > >> > We haven't considered: >> > >> > 3. Forbid faults (other than MCE) inside NMI. >> >> I'd really prefer #2. #3 depends on us getting many things right, and >> never introducing new cases in the future. >> >> #2, in contrast, seems to be fairly localized. Yes, RF is an issue, >> but returning to user space with RF clear doesn't really seem to be >> all that problematic. > > What's the worst case that can happen with RF cleared when returing > to user space ? My understanding is that it's just that we risk to > break again on an instruction that had a break point set and which > already triggered the breakpoint, right ? I assume Linus meant returning to kernel space with RF clear. Returns to userspace have their own fancy logic here, and it's survived for a couple of releases, including through an explicit test of RF handling :) --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/