Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932098Ab3JQUjW (ORCPT ); Thu, 17 Oct 2013 16:39:22 -0400 Received: from mail-qc0-f179.google.com ([209.85.216.179]:54401 "EHLO mail-qc0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758245Ab3JQUjU (ORCPT ); Thu, 17 Oct 2013 16:39:20 -0400 MIME-Version: 1.0 X-Originating-IP: [2620:0:1000:1b02:6e3b:e5ff:fe16:f1aa] In-Reply-To: <52603CD6.6080507@linux.intel.com> References: <52603CD6.6080507@linux.intel.com> Date: Thu, 17 Oct 2013 13:39:20 -0700 Message-ID: Subject: Re: Corrupted low memory in v3.9+ From: Olof Johansson To: "H. Peter Anvin" Cc: "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2841 Lines: 64 On Thu, Oct 17, 2013 at 12:39 PM, H. Peter Anvin wrote: > On 10/17/2013 11:57 AM, Olof Johansson wrote: >> >> And the low memory checker never even ran before, since it had nothing >> to check. Earlier the lower reserved region would be included in the >> e820-reserved area if I read the code correctly, and now it's just >> marked reserved by the memblock code. >> >> I guess it could be argued either way whether this is a regression or >> not; but at the end of the day we now have systems where this warning >> pops when it didn't use to. :( >> > > I'm wondering if this is a problem with the low memory checker (the > residual value of which I have to admit to being skeptical of) or > something else. There's a chance that it's a valid trip of the low-memory checker, i.e. that we do have a bios (or more likely smm), that stomps on that memory -- it was never checked for in the past and definitely not warned about. I'm not sure if that was intentional behavior or not (to not check this area), I lack history on the topic. > Could you boot the box with "debug memblock=debug" and earlyprintk > turned on and send the boot output? Ah, yes, I did verify that the first 64K were indeed set aside as reserved by doing just that: [ 0.000000] MEMBLOCK configuration: [ 0.000000] memory size = 0x7c750000 reserved size = 0xb05000 [ 0.000000] memory.cnt = 0x6 [ 0.000000] memory[0x0] [0x00000000010000-0x0000000009ffff], 0x90000 bytes [ 0.000000] memory[0x1] [0x00000000100000-0x00000000efffff], 0xe00000 bytes [ 0.000000] memory[0x2] [0x00000001000000-0x0000001fffffff], 0x1f000000 bytes [ 0.000000] memory[0x3] [0x00000020200000-0x0000003fffffff], 0x1fe00000 bytes [ 0.000000] memory[0x4] [0x00000040200000-0x0000007c6bffff], 0x3c4c0000 bytes [ 0.000000] memory[0x5] [0x00000100000000-0x000001005fffff], 0x600000 bytes [ 0.000000] reserved.cnt = 0x2 [ 0.000000] reserved[0x0] [0x0000000009f000-0x000000000fffff], 0x61000 bytes [ 0.000000] reserved[0x1] [0x00000001000000-0x00000001aa3fff], 0xaa4000 bytes [ 0.000000] memblock_reserve: [0x00000000099000-0x0000000009f000] reserve_real_mode+0x61/0x87 [ 0.000000] Base memory trampoline at [ffff880000099000] 99000 size 24576 [ 0.000000] reserving inaccessible SNB gfx pages [ 0.000000] memblock_reserve: [0x00000000000000-0x00000000100000] setup_arch+0xa2d/0xa41 [...] Unfortunately x86 doesn't keep the memblock structures around, so there's no way to verify after booting in debugfs, but based on the above it should have been reserved properly. -Olof -- 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/