[parisc-linux] memory management issues

[Ollie Wild]

> Really, given the page is already present and cached in user space, why
> not just copy through the user mappings instead of trying to map the
> pages into the kernel an then fix up coherence issues, copy then push
> the coherency back to the user ... the API you want is copy_in_user().

This doesn't work because we're copying between two different
mm_struct's.  Since we can't have both active at the same time, we
need to setup some sort of temporary mapping.

I could maybe check the vma boundaries and create new pages in the
kernel, but I still need to assign them to the process space to make
them swappable.  Since some binfmt's remove args, I'll also
potentially need to reload old pages, which means copy_strings() will
still need to call get_user_pages() to retrieve potentially swapped
out pages.

Ollie