[PATCH v10 1/9] powerpc: Allow clearing and restoring registers independent of saved breakpoint state

[Benjamin Gray]

From: Jordan Niethe <jniethe5 at gmail.com>

For the coming temporary mm used for instruction patching, the
breakpoint registers need to be cleared to prevent them from
accidentally being triggered. As soon as the patching is done, the
breakpoints will be restored.

The breakpoint state is stored in the per-cpu variable current_brk[].
Add a suspend_breakpoints() function which will clear the breakpoint
registers without touching the state in current_brk[]. Add a pair
function restore_breakpoints() which will move the state in
current_brk[] back to the registers.

Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
Signed-off-by: Benjamin Gray <bgray at linux.ibm.com>
---
v10:	* Unchanged
v9:	* Renamed ____set_breakpoint to set_hw_breakpoint
	* Renamed pause/unpause to suspend/restore
	* Removed unrelated whitespace change
---
 arch/powerpc/include/asm/debug.h |  2 ++
 arch/powerpc/kernel/process.c    | 38 +++++++++++++++++++++++++++++---
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/debug.h b/arch/powerpc/include/asm/debug.h
index 86a14736c76c..51c744608f37 100644
--- a/arch/powerpc/include/asm/debug.h
+++ b/arch/powerpc/include/asm/debug.h
@@ -46,6 +46,8 @@ static inline int debugger_fault_handler(struct pt_regs *regs) { return 0; }
 #endif
 
 void __set_breakpoint(int nr, struct arch_hw_breakpoint *brk);
+void suspend_breakpoints(void);
+void restore_breakpoints(void);
 bool ppc_breakpoint_available(void);
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
 extern void do_send_trap(struct pt_regs *regs, unsigned long address,
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 67da147fe34d..5d5109ed01a5 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -862,10 +862,8 @@ static inline int set_breakpoint_8xx(struct arch_hw_breakpoint *brk)
 	return 0;
 }
 
-void __set_breakpoint(int nr, struct arch_hw_breakpoint *brk)
+static void set_hw_breakpoint(int nr, struct arch_hw_breakpoint *brk)
 {
-	memcpy(this_cpu_ptr(&current_brk[nr]), brk, sizeof(*brk));
-
 	if (dawr_enabled())
 		// Power8 or later
 		set_dawr(nr, brk);
@@ -879,6 +877,12 @@ void __set_breakpoint(int nr, struct arch_hw_breakpoint *brk)
 		WARN_ON_ONCE(1);
 }
 
+void __set_breakpoint(int nr, struct arch_hw_breakpoint *brk)
+{
+	memcpy(this_cpu_ptr(&current_brk[nr]), brk, sizeof(*brk));
+	set_hw_breakpoint(nr, brk);
+}
+
 /* Check if we have DAWR or DABR hardware */
 bool ppc_breakpoint_available(void)
 {
@@ -891,6 +895,34 @@ bool ppc_breakpoint_available(void)
 }
 EXPORT_SYMBOL_GPL(ppc_breakpoint_available);
 
+/* Disable the breakpoint in hardware without touching current_brk[] */
+void suspend_breakpoints(void)
+{
+	struct arch_hw_breakpoint brk = {0};
+	int i;
+
+	if (!ppc_breakpoint_available())
+		return;
+
+	for (i = 0; i < nr_wp_slots(); i++)
+		set_hw_breakpoint(i, &brk);
+}
+
+/*
+ * Re-enable breakpoints suspended by suspend_breakpoints() in hardware
+ * from current_brk[]
+ */
+void restore_breakpoints(void)
+{
+	int i;
+
+	if (!ppc_breakpoint_available())
+		return;
+
+	for (i = 0; i < nr_wp_slots(); i++)
+		set_hw_breakpoint(i, this_cpu_ptr(&current_brk[i]));
+}
+
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 
 static inline bool tm_enabled(struct task_struct *tsk)
-- 
2.38.1