AGP aperture beyond 4GB not valid?

AGP aperture beyond 4GB not valid?

[Chris Adams]

I have an MSI K9A Platinum motherboard (AMD CrossFire 580X and SB600
chipset) with 4G RAM, and I'm running Fedora 9 (x86_64) with kernel
2.6.25.11-97.fc9.x86_64.  When I boot, I see the following go by:

Checking aperture...
Node 0: aperture @ 1006000000 size 32 MB
Aperture beyond 4GB. Ignoring.
No AGP bridge found
Your BIOS doesn't leave a aperture memory hole
Please enable the IOMMU option in the BIOS setup
This costs you 64 MB of RAM
Mapping aperture over 65536 KB of RAM @ c000000
PM: Registered nosave memory: 000000000c000000 - 0000000010000000


My BIOS doesn't have an IOMMU option (latest BIOS available for the
mboard).  However, it appears that an aperture is allocated but the
kernel then ignores it due to where it is placed.  Why?

Is there anything I can or should do about this (what impact does this
really have)?

-- 
Chris Adams <cmadams@hiwaay.net>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.

Re: AGP aperture beyond 4GB not valid?

[Andi Kleen]

Chris Adams <cmadams@hiwaay.net> writes:
>
> My BIOS doesn't have an IOMMU option (latest BIOS available for the
> mboard).  However, it appears that an aperture is allocated but the
> kernel then ignores it due to where it is placed.  Why?

32MB is normally not a useful aperture. Likely it's some garbage 
value the BIOS is leaving in the registers.

> Is there anything I can or should do about this (what impact does this
> really have)?

It will eat your babies. No really except for some lost RAM nothing.

-Andi

Re: AGP aperture beyond 4GB not valid?

[H. Peter Anvin]

Chris Adams wrote:
> 
> Checking aperture...
> Node 0: aperture @ 1006000000 size 32 MB
> Aperture beyond 4GB. Ignoring.
> No AGP bridge found
> Your BIOS doesn't leave a aperture memory hole
> Please enable the IOMMU option in the BIOS setup
> This costs you 64 MB of RAM
> Mapping aperture over 65536 KB of RAM @ c000000
> PM: Registered nosave memory: 000000000c000000 - 0000000010000000
> 
> 
> My BIOS doesn't have an IOMMU option (latest BIOS available for the
> mboard).  However, it appears that an aperture is allocated but the
> kernel then ignores it due to where it is placed.  Why?
> 

You can't use it as an IOMMU to handle 32-bit devices, since it's above 
the 32-bit addressible region.  Hence the kernel doesn't use it.

	-hpa