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H A Dprocess.cdiff 252988cbf037f3d446eea222afb46cc134d32c71 Sun Apr 01 07:50:36 CEST 2018 Nicholas Piggin <npiggin@gmail.com> powerpc: Don't write to DABR on >= Power8 if DAWR is disabled

flush_thread() calls __set_breakpoint() via set_debug_reg_defaults()
without checking ppc_breakpoint_available(). On Power8 or later CPUs
which have the DAWR feature disabled that will cause a write to the
DABR which is incorrect as those CPUs don't have a DABR.

Fix it two ways, by checking ppc_breakpoint_available() in
set_debug_reg_defaults(), and also by reworking __set_breakpoint() to
only write to DABR on Power7 or earlier.

Fixes: 9654153158d3 ("powerpc: Disable DAWR in the base POWER9 CPU features")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Rework the logic in __set_breakpoint()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>