Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752804AbaBYDuY (ORCPT ); Mon, 24 Feb 2014 22:50:24 -0500 Received: from terminus.zytor.com ([198.137.202.10]:46922 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751660AbaBYDuX (ORCPT ); Mon, 24 Feb 2014 22:50:23 -0500 Message-ID: <530C12CA.6070308@zytor.com> Date: Mon, 24 Feb 2014 19:49:30 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: Peter Zijlstra , Steven Rostedt CC: Vince Weaver , Linux Kernel , Ingo Molnar , "H.J. Lu" Subject: Re: perf_fuzzer compiled for x32 causes reboot References: <18f0cea3-7e3b-4477-b433-0269f3de976b@email.android.com> <20140224172536.GD9987@twins.programming.kicks-ass.net> <530B841F.5050803@zytor.com> <530B90A5.3090302@zytor.com> <20140224141329.1cd3bb52@gandalf.local.home> <20140224193043.GP6835@laptop.programming.kicks-ass.net> In-Reply-To: <20140224193043.GP6835@laptop.programming.kicks-ass.net> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/24/2014 11:30 AM, Peter Zijlstra wrote: > On Mon, Feb 24, 2014 at 02:13:29PM -0500, Steven Rostedt wrote: >> Ah, and x86_64 saves off the cr2 register when entering NMI and restores >> it before returning. But it seems to be missing from the i386 code. > > arch/x86/kernel/nmi.c: > > #define nmi_nesting_preprocess(regs) \ > do { \ > if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) { \ > this_cpu_write(nmi_state, NMI_LATCHED); \ > return; \ > } \ > this_cpu_write(nmi_state, NMI_EXECUTING); \ > this_cpu_write(nmi_cr2, read_cr2()); \ > } while (0); \ > nmi_restart: > > #define nmi_nesting_postprocess() \ > do { \ > if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) \ > write_cr2(this_cpu_read(nmi_cr2)); \ > if (this_cpu_dec_return(nmi_state)) \ > goto nmi_restart; \ > } while (0) > > That very much looks like saving/restoring CR2 to me. > > FWIW; I hate how the x86_64 and i386 versions of this NMI nesting magic > are so completely different. Is there any way that nmi_cr2 can end up getting overwritten by multiple nestings of some kind? I would have thought it would have made more sense to spill cr2 onto the stack after the stack has been properly set up. -hpa -- 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/