From: Lukas Razik <linux-GLgANOly0l1BDLzU/O5InQ@public.gmane.org>
Date: Wed, 16 Nov 2011 19:22:34 +0000 (GMT)

I'm wondering if the bug is in the mlx4 code or in the sparc
io_remap_pfn_range()
code.  From the "Bad page map" pte value, if I understand sparc mm correctly,
the PTE is seen as not present.

The not-present test is essentially testing the PTE against zero.

This bug check is making sure that there are not already existing mappings
at that address when the io_remap_pfn_range() call occurs.

x86 uses remap_pfn_range() as the implementation of it's
io_remap_pfn_range() and it also has the same exact assertion
check, in remap_pte_range().

I can't see any obvious bug in the mlx4 mmap method.

The only thing I can come up with is that perhaps there is an assumption
hiding around somewhere that PAGE_SIZE is 4096.  Such an assumption would
go undetected on both 32-bit and 64-bit x86 platforms since PAGE_SIZE is
4096 there.  Whereas on sparc64 it is 8192.
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