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Is IOMMU enabled?

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http://www.linuxquestions.org – I am developing a driver and am trying to enable IOMMU on an x86_64 AMD Opteron platform and RHEL 4.6 (kernel 2.6.9-67.0.10.ELlargesmp) with memory >4GB. The IOMMU setting is enabled in the BIOS. There is no size setting so I pass "iommu=memaper=4" kernel boot option to set the size to 512M. In the kernel messages, I see: kernel: Checking aperture... kernel: Your BIOS doesn't leave a aperture memory hole kernel: Please enable the IOMMU option in the BIOS setup kernel: This costs you 512 MB of RAM kernel: Mapping aperture over 524288 KB of RAM @ 60000000 but later in dmesg, I see (HowTos)