Re: UVM and the NULL page

[Eduardo Horvath <eeh%NetBSD.org@localhost>]

On Sat, 30 Jul 2016, Joerg Sonnenberger wrote:

> For what it is worth, I do believe that the handling of the 0 page
> should be part of UVM and not pmap. I am only objection to forcing it
> unconditionally.

I disagree.  Based on the number of files you need to touch it's much 
better to implement it in pmap.  All you need to do is check the VA in 
pmap_enter and if it's 0 return an error.  Done.  It only affects the 
particular architectures that have this problem.  You don't further 
complicate the UVM code, you don't need to instrument all the different 
syscall entries, and you don't have to worry about possibly missing some 
obscure path to get page zero mapped in to some process.

Edaurdo