mm: variable length argument support

mm: variable length argument support

Remove the arg+env limit of MAX_ARG_PAGES by copying the strings directly from
the old mm into the new mm.

We create the new mm before the binfmt code runs, and place the new stack at
the very top of the address space.  Once the binfmt code runs and figures out
where the stack should be, we move it downwards.

It is a bit peculiar in that we have one task with two mm's, one of which is
inactive.

[[email protected]: limit stack size]
Signed-off-by: Ollie Wild <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: <[email protected]>
Cc: Hugh Dickins <[email protected]>
[[email protected]: unexport bprm_mm_init]
Signed-off-by: Adrian Bunk <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>