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>

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 24a591b4dbe9fda025e91cedabb34950af498809..1237f13fed51862cbb5d7d2117c686cc06b2852b 100644 (file)
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -718,7 +718,8 @@ static void set_debug_reg_defaults(struct thread_struct *thread)
 {
        thread->hw_brk.address = 0;
        thread->hw_brk.type = 0;
-       set_breakpoint(&thread->hw_brk);
+       if (ppc_breakpoint_available())
+               set_breakpoint(&thread->hw_brk);
 }
 #endif /* !CONFIG_HAVE_HW_BREAKPOINT */
 #endif /* CONFIG_PPC_ADV_DEBUG_REGS */
@@ -815,9 +816,14 @@ void __set_breakpoint(struct arch_hw_breakpoint *brk)
        memcpy(this_cpu_ptr(&current_brk), brk, sizeof(*brk));
 
        if (cpu_has_feature(CPU_FTR_DAWR))
+               // Power8 or later
                set_dawr(brk);
-       else
+       else if (!cpu_has_feature(CPU_FTR_ARCH_207S))
+               // Power7 or earlier
                set_dabr(brk);
+       else
+               // Shouldn't happen due to higher level checks
+               WARN_ON_ONCE(1);
 }
 
 void set_breakpoint(struct arch_hw_breakpoint *brk)