Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752728AbaAQQ4d (ORCPT ); Fri, 17 Jan 2014 11:56:33 -0500 Received: from terminus.zytor.com ([198.137.202.10]:57660 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751965AbaAQQ4b (ORCPT ); Fri, 17 Jan 2014 11:56:31 -0500 Message-ID: <52D95F77.4030908@zytor.com> Date: Fri, 17 Jan 2014 08:51:03 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Borislav Petkov , "Ren, Qiaowei" CC: Thomas Gleixner , Ingo Molnar , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , Steven Rostedt Subject: Re: [PATCH 2/5] x86, mpx: hook #BR exception handler to allocate bound tables References: <1389518403-7715-1-git-send-email-qiaowei.ren@intel.com> <1389518403-7715-2-git-send-email-qiaowei.ren@intel.com> <20140112092019.GA3664@pd.tnic> <52D35ABB.8070904@intel.com> <20140113103808.GC5388@pd.tnic> <9E0BE1322F2F2246BD820DA9FC397ADE014E575D@SHSMSX102.ccr.corp.intel.com> <20140117164736.GE8715@pd.tnic> In-Reply-To: <20140117164736.GE8715@pd.tnic> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/17/2014 08:47 AM, Borislav Petkov wrote: > > Right, so Steve and I played a couple of scenarios in IRC with this. So > #BR is comparable with #PF, AFAICT, and as expected we don't take any > locks when handling page faults in kernel space as we might deadlock. > > Now, what happens if a thread is sleeping on some lock down that > GFP_KERNEL allocation path and another thread gets a #BR and goes that > same mmap_pgoff path and tries to grab that same lock? It goes to sleep. Same as if we take a page fault and have to page something in. > Also, what happens if you take a #BR in NMI context, say the NMI > handler? You should never, ever do that. We should never take a #BR in the kernel, full stop -- if we do it is panic time. > All I'm trying to say is, it might not be such a good idea to sleep in a > fault handler... A fault handler from user space is really nothing other than a different kind of system call. It is nothing magic about it. -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/