Re: UVM and the NULL page

[Maxime Villard <max%m00nbsd.net@localhost>]

Le 29/07/2016 à 05:59, Matt Thomas a écrit :
> That is not true.  Older ARM processors use a vector page located at 0 which
> has to be mapped into each processes address space.
>
> Now while the VA is mapped but it does not need to be writeable.

You didn't understand what I said. The fact is that __USER_VA0_IS_SAFE is
never set, and that therefore even old ARMs are not supposed to allow NULL
to be mapped by userland.

I don't know how ARM works, but according to what you say, I would guess
the vector page is set via pmap when creating processes, which has nothing
to do with the process itself asking for NULL to be available. So, it was
not my point.

Anyway, the only thing I'm suggesting is doing it in amd64, so this is a
little off-topic.