From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755958Ab3KVPZa (ORCPT ); Fri, 22 Nov 2013 10:25:30 -0500 Received: from terminus.zytor.com ([198.137.202.10]:40144 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755783Ab3KVPZ2 (ORCPT ); Fri, 22 Nov 2013 10:25:28 -0500 Message-ID: <528F7735.9010209@zytor.com> Date: Fri, 22 Nov 2013 07:24:37 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Vivek Goyal , Greg KH CC: linux-kernel@vger.kernel.org, kexec@lists.infradead.org, ebiederm@xmission.com, mjg59@srcf.ucam.org Subject: Re: [PATCH 5/6] kexec-bzImage: Support for loading bzImage using 64bit entry References: <1384969851-7251-1-git-send-email-vgoyal@redhat.com> <1384969851-7251-6-git-send-email-vgoyal@redhat.com> <20131121190710.GD17070@kroah.com> <20131121192114.GN16208@redhat.com> In-Reply-To: <20131121192114.GN16208@redhat.com> 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 11/21/2013 11:21 AM, Vivek Goyal wrote: >> >> What do you mean by the "real mode entry"? Do we need to care about >> that because we aren't falling back to real mode when executing this, >> are we? Or does that just happen for 32bit kernels? > > Original kexec offers real mode entry choice too. So we fall back > to real mode and jump to kernel and kernel makes bunch of BIOS calls. I > don't think this is a commonly used option. > I know some users of it (who I shall not name.) In general it is a bad option, because after running the first kernel the state of the hardware is not guaranteed to be such that executing the BIOS is safe. In general, I do think they do it just because they tried at some point and it happened to work; discouraging its use is probably for the better. -hpa