The "Out of IOMMU space" error and the "Please enable the IOMMU option" option

Occasionally, we get errors like these:

Jun 9 00:56:35 [kernel] [18020.416620] PCI-DMA: Out of IOMMU space for 12288 bytes at device 0000:03:01.0

and it looks like it might have something to do with these messages (after updating and setting BIOS as below):

Jun 15 16:38:54 [kernel] [ 0.000000] Checking aperture...
Jun 15 16:38:54 [kernel] [ 0.000000] CPU 0: aperture @ 0 size 256 MB
Jun 15 16:38:54 [kernel] [ 0.000000] No AGP bridge found
Jun 15 16:38:54 [kernel] [ 0.000000] Your BIOS doesn't leave a aperture memory hole
Jun 15 16:38:54 [kernel] [ 0.000000] Please enable the IOMMU option in the BIOS setup
Jun 15 16:38:54 [kernel] [ 0.000000] This costs you 64 MB of RAM
Jun 15 16:38:54 [kernel] [ 0.000000] Mapping aperture over 65536 KB of RAM @ 8000000

The box is a dual Opteron 250 with an Arima HDAMA Rev. D motherboard.

The updated BIOS options are (with * for current setting)
MTRR mapping method [Continuous, Discrete*]
Memhole mapping [Software, Hardware*]
4 GB memory hole adjust [Disabled, Manual, Auto*]
4 GB memory hole size [128 MB]
IOMMU [Disabled, Enabled*]
Size [multiple sizes, 256 MB*]

Initially, I was booting kernel 2.6.16.1 with iommu=merge, but the above message still occur when I booted without any iommu kernel parameters.

First, am I correct to assume that I'm not getting the 256 MB?

Second, is the the case the BIOS is lying?

Third, what could be a workaround to get enough memory for the PCI card that causes the out of space error (3Ware 8506)?
--

Maurice Volaski, mvolaski@xxxxxxxxxxxx
Computing Support, Rose F. Kennedy Center
Albert Einstein College of Medicine of Yeshiva University
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