Re: [PATCH] report user-readable fixmap area in /proc/PID/maps

[Roland McGrath]

> This special-casing, and the special-casing in get_user_pages() would go
> away if each process had a real VMA for the fixmap area inserted into its
> VMA tree.

Agreed.

> Remind me again why we cannot do that?

I don't know any reason to think we cannot.  That's not the way it was done
when I first looked at fixmap issues, and I try not to rock the boat more
than necessary (really!).  I know that Ingo had some kernel versions that
used a normal vma for it (and randomized the location on each exec), so he
certainly managed it.  I always assumed that people (i.e. Linus) wouldn't
like it because of the overhead in memory and setup time for an extra vma
that is identical in every process.  Given the constraint that the fixmap
area is the last thing in the address space, I imagine that can be
mitigated by some magic using a single shared fixmap_vma at the end of
everybody's chain.
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