From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751681AbcBLPe0 (ORCPT ); Fri, 12 Feb 2016 10:34:26 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41466 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751060AbcBLPeO (ORCPT ); Fri, 12 Feb 2016 10:34:14 -0500 Date: Fri, 12 Feb 2016 23:34:07 +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: About support XZ-compressed kernel on x86 Message-ID: <20160212153407.GA2731@x1.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 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. Thanks Baoquan