CVE-2017-5754

BugLink: http://bugs.launchpad.net/bugs/1742772

This puts a nop before each rfid/hrfid and patches in an L1-D
cache flush instruction where possible.

It provides /sys/devices/system/cpu/rfi_flush which can report and can
patch the rfi flushes at runtime.

This has some debug checking in the rfi instructions to make sure
we're returning to the context we think we are, so we can avoid
some flushes.

Includes support for querying the device tree, or hypervisor, to
determine the platform's capabilities and requirements. Also includes
an implementation of the hcall for KVM guests.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>