After v4.6 released, a number of people complained that Linux's use of
__ro_after_init was extremely limited, but they did not send patches. In
the interest of showing how to make progress in this area, this is a
set of two patches for x86 and arm, extracted from the grsecurity/PaX
patchset in about an hour. I invite others to continue this work, as it
is relatively easy to accomplish.

Since __ro_after_init doesn't yet support modules (assistence here is
welcome too), markings can only be used on variables that are built
in. And since PaX mixes variables that are read-only after init with
those that are protected with pax_open_kernel() and pax_close_kernel(),
it does take a bit of analysis to make sure the variables aren't used
in those cases.

Thanks,

-Kees