[Bug 12222] kernel BUG at drivers/pci/intel-iommu.c:1373!

[bugme-daemon@bugzilla.kernel.org]

http://bugzilla.kernel.org/show_bug.cgi?id=12222





------- Comment #4 from grundler@parisc-linux.org  2008-12-15 13:40 -------
In 2.6.28-rc8 kernel, the BUG_ON is now at line 1276.
The BUG_ON is just indicating the IOMMU page table entry is already (or still)
in use.

My guess is either the IOMMU space allocator is buggy *OR* the unmap code isn't
clearing dma_pte_addr() (off by one?). Perhaps there needs to be a wmb() in
intel_unmap_sg() between dma_pte_clear_range() and the later __free_iova()
call.

intel_iommu=off means no IOMMU will be used. For normal workloads with modern
PCIe devices (which are all 64-bit, right?), there would be no perf impact. Not
until you wanted to get better isolation for virtual guest OSs or used a device
driver that only offers 32-bit DMA support, will it matter.


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