Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752570Ab3EJMIx (ORCPT ); Fri, 10 May 2013 08:08:53 -0400 Received: from terminus.zytor.com ([198.137.202.10]:37322 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751785Ab3EJMIv (ORCPT ); Fri, 10 May 2013 08:08:51 -0400 Date: Fri, 10 May 2013 05:08:23 -0700 From: tip-bot for Zhang Yanfei Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, konrad.wilk@oracle.com, zhangyanfei@cn.fujitsu.com, akpm@linux-foundation.org, isimatu.yasuaki@jp.fujitsu.com, tglx@linutronix.de Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, konrad.wilk@oracle.com, zhangyanfei@cn.fujitsu.com, akpm@linux-foundation.org, isimatu.yasuaki@jp.fujitsu.com, tglx@linutronix.de In-Reply-To: <518BC776.7010506@gmail.com> References: <518BC776.7010506@gmail.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/mm: Add missing comments for initial kernel direct mapping Git-Commit-ID: cf8b166d5c1c89aad6c436a954fa40fd18a75bfb X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3105 Lines: 76 Commit-ID: cf8b166d5c1c89aad6c436a954fa40fd18a75bfb Gitweb: http://git.kernel.org/tip/cf8b166d5c1c89aad6c436a954fa40fd18a75bfb Author: Zhang Yanfei AuthorDate: Thu, 9 May 2013 23:57:42 +0800 Committer: Ingo Molnar CommitDate: Fri, 10 May 2013 12:00:35 +0200 x86/mm: Add missing comments for initial kernel direct mapping Two sets of comments were lost during patch-series shuffling: - comments for init_range_memory_mapping() - comments in init_mem_mapping that is helpful for reminding people that the pagetable is setup top-down The comments were written by Yinghai in his patch in: https://lkml.org/lkml/2012/11/28/620 This patch reintroduces them. Originally-From: Yinghai Lu Signed-off-by: Zhang Yanfei Cc: Yasuaki Ishimatsu Cc: Konrad Rzeszutek Wilk Cc: Andrew Morton Link: http://lkml.kernel.org/r/518BC776.7010506@gmail.com [ Tidied it all up a bit. ] Signed-off-by: Ingo Molnar --- arch/x86/mm/init.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index fdc5dca..eaac174 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -359,7 +359,17 @@ unsigned long __init_refok init_memory_mapping(unsigned long start, } /* - * would have hole in the middle or ends, and only ram parts will be mapped. + * We need to iterate through the E820 memory map and create direct mappings + * for only E820_RAM and E820_KERN_RESERVED regions. We cannot simply + * create direct mappings for all pfns from [0 to max_low_pfn) and + * [4GB to max_pfn) because of possible memory holes in high addresses + * that cannot be marked as UC by fixed/variable range MTRRs. + * Depending on the alignment of E820 ranges, this may possibly result + * in using smaller size (i.e. 4K instead of 2M or 1G) page tables. + * + * init_mem_mapping() calls init_range_memory_mapping() with big range. + * That range would have hole in the middle or ends, and only ram parts + * will be mapped in init_range_memory_mapping(). */ static unsigned long __init init_range_memory_mapping( unsigned long r_start, @@ -419,6 +429,13 @@ void __init init_mem_mapping(void) max_pfn_mapped = 0; /* will get exact value next */ min_pfn_mapped = real_end >> PAGE_SHIFT; last_start = start = real_end; + + /* + * We start from the top (end of memory) and go to the bottom. + * The memblock_find_in_range() gets us a block of RAM from the + * end of RAM in [min_pfn_mapped, max_pfn_mapped) used as new pages + * for page table. + */ while (last_start > ISA_END_ADDRESS) { if (last_start > step_size) { start = round_down(last_start - 1, step_size); -- 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/