[coreboot] memtest86 reading 0k memory

[Timothy Pearson]

On 02/05/2015 02:06 PM, Timothy Pearson wrote:
> On 02/05/2015 01:51 PM, Aaron Durbin wrote:
>> Do you have the coreboot console log? Looking at memtest86 it
>> constructs its own e820 when using linuxbios. Additionally, it also
>> has some concept of a "window" to test as well as plim_lower and
>> plim_upper variables that seem to add to the mix.
>>
>> What's super frightening is that find_chunks(int tst) is called in the
>> code as find_chunks() while the find_chunks() function actually
>> references tst as an array index. That's all from config.c. But I
>> think that's only if you hit c on the keyboard. I wouldn't do that...
>>
>> I can't make heads or tails of that code at the moment. for selecting
>> the window to test.
>
> Please see text log attached. It looks like the failing accesses start
> at 0xa0000, which (judging by memtest's effects on the screen) appears
> to be mapped to the VGA text buffer. That region is *not* reserved under
> the proprietary BIOS's e820 map.
>
> Thanks!
>

I was able to resolve the lower MMIO region failures (coreboot driver 
patch in for review), but memtest86 is stubbornly insisting on testing 
reserved memory, causing a single failure at 3ffade80.  The e820 map 
says that address is out of bounds but the coreboot tables do not:

e820 map has 6 items:
   0: 0000000000000000 - 000000000009fc00 = 1 RAM
   1: 000000000009fc00 - 00000000000a0000 = 2 RESERVED
   2: 00000000000f0000 - 0000000000100000 = 2 RESERVED
   3: 0000000000100000 - 000000003ffad000 = 1 RAM
   4: 000000003ffad000 - 0000000040000000 = 2 RESERVED
   5: 00000000e0000000 - 00000000f0000000 = 2 RESERVED

coreboot table: 460 bytes.
CBMEM ROOT  0. 3ffff000 00001000
CONSOLE     1. 3ffdf000 00020000
TIME STAMP  2. 3ffde000 00001000
GDT         3. 3ffdd000 00001000
SMP TABLE   4. 3ffdc000 00001000
ACPI        5. 3ffb8000 00024000
SMBIOS      6. 3ffb7000 00001000
COREBOOT    7. 3ffaf000 00008000

Why the discrepancy?  Am I correct in assuming this is a bug in coreboot 
that needs to be fixed?

-- 
Timothy Pearson
Raptor Engineering
+1 (415) 727-8645
http://www.raptorengineeringinc.com