From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753343AbaE0SqI (ORCPT ); Tue, 27 May 2014 14:46:08 -0400 Received: from mga02.intel.com ([134.134.136.20]:60317 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752868AbaE0SqE (ORCPT ); Tue, 27 May 2014 14:46:04 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.98,921,1392192000"; d="scan'208";a="518520961" Message-ID: <5384DD67.3010408@intel.com> Date: Tue, 27 May 2014 11:45:59 -0700 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Matt Fleming , Andrew Morton CC: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alan Cox Subject: Re: [PATCH] mm: bootmem: Check pfn_valid() before accessing struct page References: <1401199802-10212-1-git-send-email-matt.fleming@intel.com> In-Reply-To: <1401199802-10212-1-git-send-email-matt.fleming@intel.com> 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 05/27/2014 07:10 AM, Matt Fleming wrote: > We need to check that a pfn is valid before handing it to pfn_to_page() > since on low memory systems with CONFIG_HIGHMEM=n it's possible that a > pfn may not have a corresponding struct page. > > This is in fact the case for one of Alan's machines where some of the > EFI boot services pages live in highmem, and running a kernel without > CONFIG_HIGHMEM enabled results in the following oops ... > diff --git a/mm/bootmem.c b/mm/bootmem.c > index 90bd3507b413..406e9cb1d58c 100644 > --- a/mm/bootmem.c > +++ b/mm/bootmem.c > @@ -164,6 +164,9 @@ void __init free_bootmem_late(unsigned long physaddr, unsigned long size) > end = PFN_DOWN(physaddr + size); > > for (; cursor < end; cursor++) { > + if (!pfn_valid(cursor)) > + continue; > + > __free_pages_bootmem(pfn_to_page(cursor), 0); > totalram_pages++; > } I don't think this is quite right. pfn_valid() tells us whether we have a 'struct page' there or not. *BUT*, it does not tell us whether it is RAM that we can actually address and than can be freed in to the buddy allocator. I think sparsemem is where this matters. Let's say mem= caused lowmem to end in the middle of a section (or that 896MB wasn't section-aligned). Then someone calls free_bootmem_late() on an area that is in the last section, but _above_ max_mapnr. It'll be pfn_valid(), we'll free it in to the buddy allocator, and we'll blam the first time we try to write to a bogus vaddr after a phys_to_virt(). At a higher level, I don't like the idea of the bootmem code papering over bugs when somebody calls in to it trying to _free_ stuff that's not memory (as far as the kernel is concerned). I think the right thing to do is to call in to the e820 code and see if the range is E820_RAM before trying to bootmem-free it.