[coreboot] memtest86 reading 0k memory

[Carl-Daniel Hailfinger]

On 08.04.2015 22:55, Stefan Tauner wrote:
> On Thu, 19 Feb 2015 10:43:44 -0500
> "Kevin O'Connor" <kevin at koconnor.net> wrote:
>
>> On Wed, Feb 18, 2015 at 10:26:21PM +0100, Stefan Reinauer wrote:
>>> * Timothy Pearson <tpearson at raptorengineeringinc.com> [150205 19:23]:
>>>> e820: BIOS-provided physical RAM map:
>>>> BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
>>>> BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
>>>> BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
>>>> BIOS-e820: [mem 0x0000000000100000-0x000000003ffacfff] usable
>>>> BIOS-e820: [mem 0x000000003ffad000-0x000000003fffffff] reserved
>>>> BIOS-e820: [mem 0x00000000e0000000-0x00000000efffffff] reserved
>>>  
>>> One of the issues seems to be that the coreboot table space is not
>>> marked as reserved (i.e. the lower 4k should be marked as reserved, and
>>> whatever is used at the top of memory)
>> coreboot tends to reserve the first 4K, but this breaks lots of
>> bootloaders.  So, SeaBIOS always overrides coreboot and unreserves the
>> first 4K.  My experience is that the first one megabyte of the e820 is
>> just "magical" and should always read as listed above.
>>
>> Separately, it is possible for SeaBIOS to remove the coreboot table
>> forwarder, and thus force memtest86 to not use the coreboot tables.
>> I'm not sure if this would affect other programs though.
> I ran into the problem today when trying to verify that the ASRock
> IMB-A180-H works correctly with coreboot. Is there any consensus on
> what to do? IMHO this is a bug in SeaBIOS... it creates the discrepancy
> between the tables and that leads to problems downstream... but that's
> arguable. What is not arguable: some action is required. :)

The Linux kernel expects coreboot+SeaBIOS to lie and marks the first 4K
as reserved again. Excerpt from my dmesg on a T60 running coreboot+SeaBIOS:

e820: BIOS-provided physical RAM map:
BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
BIOS-e820: [mem 0x0000000000100000-0x00000000cfec9fff] usable
BIOS-e820: [mem 0x00000000cfeca000-0x00000000cfffffff] reserved
BIOS-e820: [mem 0x00000000f0000000-0x00000000f3ffffff] reserved
SMBIOS 2.7 present.
DMI: LENOVO 2007VVT/2007VVT, BIOS CBET4000 4.0-7070-g2fc0a1d 10/18/2014
e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
e820: remove [mem 0x000a0000-0x000fffff] usable

Regards,
Carl-Daniel