From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751320AbcBLPlq (ORCPT ); Fri, 12 Feb 2016 10:41:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:53239 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750902AbcBLPlp (ORCPT ); Fri, 12 Feb 2016 10:41:45 -0500 Date: Fri, 12 Feb 2016 23:41:41 +0800 From: Baoquan He To: lasse.collin@tukaani.org Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, alain@knaff.lu, albin.tonnerre@free-electrons.com, phillip@lougher.demon.co.uk, akpm@linux-foundation.org, keescook@chromium.org, bp@alien8.de, vgoyal@redhat.com Subject: Re: About support XZ-compressed kernel on x86 Message-ID: <20160212154141.GA22864@x1.redhat.com> References: <20160212153407.GA2731@x1.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160212153407.GA2731@x1.redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/12/16 at 11:34pm, Baoquan He wrote: > Hi Lasse, > > I am checking a thread related to kaslr and setup_data issue on x86: > https://lkml.org/lkml/2015/7/7/963 > > Now I have a question about the commit from you: > > commit 303148045aac34b70db722a54e5ad94a3a6625c6 > Author: Lasse Collin > Date: Wed Jan 12 17:01:24 2011 -0800 > > x86: support XZ-compressed kernel > > > In this commit for adding support of XZ-compressed kernel on x86, you > add extra 32K to the extract_offset. In commit log you said this is > because "The XZ decompressor needs around 30 KiB of heap, so the heap > size is increased to 32 KiB on both x86-32 and x86-64." With my > understanding decompression is done in decompression stage and it uses > boot_heap in arch/x86/boot/compressed/head_64.S, and boot_heap is > assigned to free_mem_ptr which is used for decompression heap malloc. > During this decompressio stage it's still in copied ZO space, why did > you add extra 32K space to extract_offset? If you want to increase the > decompression heap space shouldn't you decrease the extract_offset? Do I > misunderstand anything or miss things? > > Please help answer, I really don't understand this. Lasse, please help have a look when it's convenient to you, many thanks. > > Thanks > Baoquan