PCI-DMA: high address but no IOMMU

[Michael Madore <michael.madore@gmail.com>]

Hi,

I am seeing the following errors in /var/log/messages when booting
2.6.14-rc5 on a dual Opteron nforce4 motherboard with 8GB of RAM:

Checking aperture...
CPU 0: aperture @ be8c000000 size 32 MB
Aperture from northbridge cpu 0 too small (32 MB)
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 @ 8000000

...

PCI-DMA: Disabling AGP.
PCI-DMA: More than 4GB of RAM and no IOMMU
PCI-DMA: 32bit PCI IO may malfunction.<6>PCI-DMA: Disabling IOMMU.

...

Attached scsi disk sda at scsi2, channel 0, id 0, lun 0
Kernel panic - not syncing: PCI-DMA: high address but no IOMMU.

With 2.6.13, the systems boots OK with these messages in the log:

Checking aperture...
CPU 0: aperture @ 8000000 size 32 MB
Aperture from northbridge cpu 0 too small (32 MB)
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 @ 8000000

...

PCI-DMA: Disabling AGP.
PCI-DMA: aperture base @ 8000000 size 65536 KB
PCI-DMA: Reserving 64MB of IOMMU area in the AGP aperture

Using git bisect, I narrowed the problem down to the following commit:

6142891a0c0209c91aa4a98f725de0d6e2ed4918 is first bad commit
diff-tree 6142891a0c0209c91aa4a98f725de0d6e2ed4918 (from
357e11d4cbbbb959a88a9bdbbf33a10f160b0823)
Author: Andi Kleen <ak@suse.de>
Date:   Mon Sep 12 18:49:24 2005 +0200

    [PATCH] x86-64: Avoid unnecessary double bouncing for swiotlb

    PCI_DMA_BUS_IS_PHYS has to be zero even when the GART IOMMU is disabled
    and the swiotlb is used. Otherwise the block layer does unnecessary
    double bouncing.

    Signed-off-by: Andi Kleen <ak@suse.de>
    Signed-off-by: Linus Torvalds <torvalds@osdl.org>

:040000 040000 d704d51d1e05f508f09c4388d3199cafbb9e3018
6a40204fd8b954634f2f7ea8f84861ed0a4bd88e M      include

Reverting this change allows 2.6.14-rc5 to boot.

Mike
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