Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932214AbVLANTE (ORCPT ); Thu, 1 Dec 2005 08:19:04 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932228AbVLANTE (ORCPT ); Thu, 1 Dec 2005 08:19:04 -0500 Received: from ns2.suse.de ([195.135.220.15]:54252 "EHLO mx2.suse.de") by vger.kernel.org with ESMTP id S932214AbVLANTD (ORCPT ); Thu, 1 Dec 2005 08:19:03 -0500 Date: Thu, 1 Dec 2005 14:18:57 +0100 From: Andi Kleen To: Zwane Mwaikambo Cc: Linux Kernel , Andi Kleen , Andrew Morton , William Lee Irwin III , "Raj, Ashok" Subject: Re: x86_64/HOTPLUG_CPU: NULL dereference doesn't #PF with init_level4_pgt Message-ID: <20051201131857.GG19515@wotan.suse.de> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 943 Lines: 21 On Wed, Nov 30, 2005 at 08:03:33PM -0800, Zwane Mwaikambo wrote: > NULL dereferences don't cause a page fault if the 4th level pagetable > being used is init_level4_pgt because we never zap_low_mappings. Since > the idle thread uses init_level4_pgt any bad dereferences happening there > (e.g. from interrupts) won't cause a fault. Andi would you be fine with > switching the idle threads to a different level4? That recently changed. Are you sure it's still the case? idle threads should always run with lazy TLB, no different mms. That's important for performance. If a NULL reference causes a oops or not depends on if user space from the last process mapped a page to NULL or not. -Andi - 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/