Provide hooks into the kernel entry and exit paths to permit control
of userspace visibility to the kernel.  The intended use is:

- on entry to kernel from user, uaccess_disable will be called to
  disable userspace visibility
- on exit from kernel to user, uaccess_enable will be called to
  enable userspace visibility
- on entry from a kernel exception, uaccess_save_and_disable will be
  called to save the current userspace visibility setting, and disable
  access
- on exit from a kernel exception, uaccess_restore will be called to
  restore the userspace visibility as it was before the exception
  occurred.

These hooks allows us to keep userspace visibility disabled for the
vast majority of the kernel, except for localised regions where we
want to explicitly access userspace.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Now that we pass r2 into these helper functions as the pointer to
pt_regs, use r2 as the base of the registers on the stack rather
than using the stack pointer directly.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Tail-call the main C data abort handler code from the per-CPU helper
code.  Update the comments in the code wrt the new calling and return
register state.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

This allows us to pass the pt_regs pointer in to these functions
ready for tail-calling the abort handler.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Re-jig the CPU abort helpers to take the PC/PSR in r4/r5 rather
than r2/r3.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

There is no FSR/FAR register on no-CP15 or MPU cores. This patch adds a
dummy abort handler which returns zero for the base restored Data Abort
model !CPU_CP15_MMU cores. The abort-lv4t.S is still used with the fix-up
for the base updated Data Abort model cores.
Signed-off-by: NHyok S. Choi <hyok.choi@samsung.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!