From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933192Ab2IUWML (ORCPT ); Fri, 21 Sep 2012 18:12:11 -0400 Received: from mga01.intel.com ([192.55.52.88]:62097 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757001Ab2IUWMJ (ORCPT ); Fri, 21 Sep 2012 18:12:09 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.80,464,1344236400"; d="scan'208";a="225258478" Message-ID: <505CE638.1030405@linux.intel.com> Date: Fri, 21 Sep 2012 15:12:08 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0 MIME-Version: 1.0 To: "Eric W. Biederman" CC: Linux Kernel Mailing List , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Kees Cook , Linda Wang , Matt Fleming Subject: Re: [PATCH 00/11] x86: Supervisor Mode Access Prevention References: <1348256595-29119-1-git-send-email-hpa@linux.intel.com> <877grnows4.fsf@xmission.com> In-Reply-To: <877grnows4.fsf@xmission.com> 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 09/21/2012 03:07 PM, Eric W. Biederman wrote: > > Have you tested kexec in this environment? > > This is the kind of cpu feature that when we enable it, frequently we > have to do something on the kexec path. > > At a quick skim it looks like the kexec path is using kernel page table > entries and clearing all bits from cr4 except X86_CR4_PAE so I don't > actually expect this change will require anything on the kexec path. > I have not, no, but as you quite correctly point out that shouldn't affect things. We should also change the kernel to start clean with CR4 -- the purpose of CR4 is to indicate which CPU features the OS is opting into. I think we do on x86-64 but not on x86-32 at the moment. This is an unrelated problem, though, and can be addressed later. -hpa