Re: [PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem)

[Greg Edwards <edwardsg@sgi.com>]

On Sat, Aug 13, 2005 at 08:18:07PM +0200, Arjan van de Ven wrote:
| On Sat, 2005-08-13 at 10:37 -0700, Linus Torvalds wrote:
| > Actually, the more I looked at that mmap_kmem() function, the less I liked 
| > it.  Let's get that sucker fixed better first. It's still not wonderful, 
| > but at least now it tries to verify the whole _range_ of the mapping.
| 
| actually if that is your goal this just isn't enough... assume the
| situation of a 1 page "forbidden gap", if you mmap 3 pages with the gap
| in the middle.... then the code you send still doesn't cope. At which
| point... it gets messy...

mmap_mem suffers from a lack of proper checks as well.  For example, on
Altix page 0 of each node is reserved for prom and a read or write to it
will cause an MCA.  mmaping /dev/mem with offset 0 will nicely explode.
Would adding a pfn_valid test in mmap_mem be the best bet, or could we
consolidate the checks currently in mmap_kmem into mmap_mem?

Greg
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