Re: 2.6.9-rc2-mm1

[Andi Kleen]

Terence Ripperda <tripperda@xxxxxxxxxx> writes:

> this is some ugly code. we're doing a lookup on a physical address to
> see if this is memory we previously allocated and returning a kernel
> pointer to the page.
>
> the particular snippet in question (that uses MAXMEM) is an ugly attempt
> to verify the address is a real physical address, before using __va()
> on something like an i/o region. A better approach than comparing
> MAXMEM would probably be to convert the address to a mapnr and compare
> to max_mapnr.

pfn_valid() is intended for that. However it cannot work 
when you have more than 4GB memory and IO memory holes below 4GB.
Testing the reserved bit of the struct page * may work in
that case, although it can give false positives when you try
this with random memory (some people set reserved on real memory
for other reason) 

-Andi

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