From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753359AbaBXTcw (ORCPT <rfc822;w@1wt.eu>);
	Mon, 24 Feb 2014 14:32:52 -0500
Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.226]:35327 "EHLO
	cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL)
	by vger.kernel.org with ESMTP id S1752764AbaBXTcv (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 24 Feb 2014 14:32:51 -0500
Date: Mon, 24 Feb 2014 14:32:49 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Vince Weaver <vincent.weaver@maine.edu>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, "H.J. Lu" <hjl.tools@gmail.com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot
Message-ID: <20140224143249.2c37e16f@gandalf.local.home>
In-Reply-To: <20140224193043.GP6835@laptop.programming.kicks-ass.net>
References: <alpine.DEB.2.10.1402241130080.20170@vincent-weaver-1.um.maine.edu>
	<18f0cea3-7e3b-4477-b433-0269f3de976b@email.android.com>
	<alpine.DEB.2.10.1402241204070.20170@vincent-weaver-1.um.maine.edu>
	<20140224172536.GD9987@twins.programming.kicks-ass.net>
	<alpine.DEB.2.10.1402241230440.20170@vincent-weaver-1.um.maine.edu>
	<530B841F.5050803@zytor.com>
	<alpine.DEB.2.10.1402241258590.20170@vincent-weaver-1.um.maine.edu>
	<alpine.DEB.2.10.1402241302210.20560@vincent-weaver-1.um.maine.edu>
	<530B90A5.3090302@zytor.com>
	<20140224141329.1cd3bb52@gandalf.local.home>
	<20140224193043.GP6835@laptop.programming.kicks-ass.net>
X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-pc-linux-gnu)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
X-RR-Connecting-IP: 107.14.168.142:25
X-Cloudmark-Score: 0
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, 24 Feb 2014 20:30:43 +0100
Peter Zijlstra <peterz@infradead.org> 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.
> 

Ah, I forgot to look in the C file.

> FWIW; I hate how the x86_64 and i386 versions of this NMI nesting magic
> are so completely different.

Yeah, it sucks. But that's because the architecture on handling NMIs is
completely different. x86_64 swaps the stack automatically, where as
i386 uses the same stack if you are already in the kernel.

-- Steve