linux-kernel - Re: BGRT Pointer in System RAM

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Date:	Tue, 16 Jul 2013 14:15:22 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Parag Warudkar <parag.lkml@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-acpi@...r.kernel.org
Subject: Re: BGRT Pointer in System RAM

On Mon, Jul 15, 2013 at 4:24 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Mon, Jul 15, 2013 at 4:20 PM, Josh Triplett <josh@...htriplett.org> wrote:
>> On Mon, Jul 15, 2013 at 04:08:13PM -0700, Andy Lutomirski wrote:
>>> On Mon, Jul 15, 2013 at 4:04 PM, Josh Triplett <josh@...htriplett.org> wrote:
>>> > On Mon, Jul 15, 2013 at 01:28:36PM -0700, Andy Lutomirski wrote:
>>> >>
>>> >> Interesting.  My BGRT says:
>>> >>
>>> >> [028h 0040   8]                Image Address : 0D06801800000001
>>> >>
>>> >> If I reverse the high and low 32-bit dwords, then I get an address in
>>> >> system RAM.
>>> >
>>> > Does that address in RAM start with a BMP header?
>>>
>>> No idea.  I'd presumably have to modify the driver to find out --
>>> otherwise something else will overwrite it.
>>
>> You could boot with a mem= command-line argument that reserves that
>> memory.
>
> I'll see what I can do.
>

I booted with mem=3G, and:

$ sudo dd bs=1 skip=4513853464 if=/dev/mem count=1
dd: reading ‘/dev/mem’: Bad address

The kernel log says nothing, which suggests that ioremap_cache is
failing.  I don't know why.

The address 4513853464 is 0x10D0BF018, which should be okay:

[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000045fffffff] usable
[    0.000000] e820: remove [mem 0xc0000000-0xfffffffffffffffe] usable

EFI agrees:
[    0.000000] efi: mem213: type=7, attr=0xf,
range=[0x0000000100000000-0x0000000460000000) (13824MB)

This could be related to the fact that mtrr cleanup is failing,
possibly due to bugs related to mem=.

That's about my tolerance for debugging something that doesn't really
deserve to work.

--Andy
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