Use fixmaps for text patching when the kernel text is read-only,
inspired by x86.  This makes jump labels and kprobes work with the
currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming
CONFIG_DEBUG_RODATA options.
Signed-off-by: NRabin Vincent <rabin@rab.in>
[kees: fixed up for merge with "arm: use generic fixmap.h"]
[kees: added parse acquire/release annotations to pass C=1 builds]
[kees: always use stop_machine to keep TLB flushing local]
Signed-off-by: NKees Cook <keescook@chromium.org>
Acked-by: NNicolas Pitre <nico@linaro.org>

Extract out the code patching code from kprobes so that it can be used
from the jump label code.  Additionally, the separated code:

 - Uses the IS_ENABLED() macros instead of the #ifdefs for THUMB2
   support

 - Unifies the two separate functions in kprobes, providing one function
   that uses stop_machine() internally, and one that can be called from
   stop_machine() directly

 - Patches the text on all CPUs only on processors requiring software
   broadcasting of cache operations
Acked-by: NJon Medhurst <tixy@yxit.co.uk>
Tested-by: NJon Medhurst <tixy@yxit.co.uk>
Signed-off-by: NRabin Vincent <rabin@rab.in>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>