Question about process/kernel address space

Stefan Nickl Stefan.Nickl at
Thu Apr 22 16:43:51 EST 2004


in some elderly code for a VME-supporting 824x-board from
our company I found the following line in ppc_md.setup_io_mappings():

io_block_mapping(0x80000000, 0x80000000, 0x10000000, _PAGE_IO);

This is obviously meant to map a window of VME IO memory into
virtual address space. What puzzles me is that the mapping is
located below PAGE_OFFSET (0xc0000000), which, from my general
understanding, is bad :(

But since apparently nobody had a problem with this for years,
(and ranges above PAGE_OFFSET are tight) I'd like to know what
the actual implications are.
Ok, should a process ever access this range, it would fail
(since the BATs go first and allow only supervisor access(?)),
but a user process ever using such a high address seems highly unlikely.

What I worry more is that it might introduce some security
holes or stability problems, any thoughts?


Stefan Nickl
Kontron Modular Computers

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