[LinuxBIOS] ACPI NVS and last 64k-ish area of RAM?

Myles Watson myles at pel.cs.byu.edu
Thu Oct 5 15:27:43 CEST 2006


I found that the best way for me to learn about this was to play with the
factory BIOS settings.

 

The memory hole allows you to boost part of memory above 4GB so that you
have more room for I/O devices without losing memory capacity.

 

For example, if you had a graphics card with 256MB of memory and 4GB of RAM
installed in the machine, you cannot address both and keep them inside
32-bits.  The solution is to use registers on the Opteron to map some of
your RAM above that limit.

 

Myles

 

  _____  

From: linuxbios-bounces at linuxbios.org
[mailto:linuxbios-bounces at linuxbios.org] On Behalf Of Alan Mimms
Sent: Wednesday, October 04, 2006 1:59 PM
To: Lu, Yinghai; linuxbios at linuxbios.org; Andi Kleen
Subject: Re: [LinuxBIOS] ACPI NVS and last 64k-ish area of RAM?

 

The problem occurs with 1GB, 2GB or 4GB of memory installed for sure.  I do
not know about the HW memory hole.  Can you explain what that is?

 

Alan Mimms, Senior Architect
F5 Networks, Inc.  Spokane Development Center
1322 North Whitman Lane
Liberty Lake, Washington   99019

v: 509-343-3524   f: 509-343-3501

 

  _____  

From: Lu, Yinghai [mailto:yinghai.lu at amd.com] 
Sent: Wednesday, October 04, 2006 12:05 PM
To: Alan Mimms; linuxbios at linuxbios.org; Andi Kleen
Subject: RE: [LinuxBIOS] ACPI NVS and last 64k-ish area of RAM?

 

What's your total RAM installed? 4G or more. With HW memory hole enable?

 

YH

 

  _____  

From: linuxbios-bounces at linuxbios.org
[mailto:linuxbios-bounces at linuxbios.org] On Behalf Of Alan Mimms
Sent: Wednesday, October 04, 2006 11:28 AM
To: linuxbios at linuxbios.org
Subject: [LinuxBIOS] ACPI NVS and last 64k-ish area of RAM?

 

We have AMD dual Opteron hardware with AMD 8131+8111 chipsets attached.
Using LinuxBIOS, we have a slight problem, that APPEARS to be related to the
last 64Kbytes of RAM.  Our kboot based environment, running in 32 bit
instruction set, seems to randomly crash, and the implicated area of memory
is this last 64KB.

 

When we run a commercial BIOS on nearly identical hardware, we see that that
BIOS has created in the E820 table an ACPI Non-Volatile-Storage area
covering this last 64KB.  LinuxBIOS is NOT doing that; LinuxBIOS is treating
all of the space as simple USABLE space.

 

In trying to figure this out, we have used the AMD HDT tool to read the last
64KB.  We (SOMETIMES) the system crashes when we read this area using HDT.

 

Can someone please explain what this area is for and why it's strange to
read even using a hardware debugging tool?  Is it REALLY in use for the ACPI
NVS, and can we simply tell Linux to ignore it (map it out) by creating an
entry in E820 table so it won't be used (we don't use ACPI suspend/resume)?

 

Thanks very much for any information.

 

Alan Mimms, Senior Architect
F5 Networks, Inc.  Spokane Development Center
1322 North Whitman Lane
Liberty Lake, Washington   99019

v: 509-343-3524   f: 509-343-3501

 

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