powerpc: Allow clearing and restoring registers independent of saved breakpoint state

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@gmail.com>
Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221109045112.187069-2-bgray@linux.ibm.com

diff --git a/arch/powerpc/include/asm/debug.h b/arch/powerpc/include/asm/debug.h
index 86a14736c76c36fa7e04de7e5a2525b73f8958b1..51c744608f37a8cc09c3514a8b7f6547a7718b39 100644 (file)
--- 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 e3e1feaa536a9938f79e7067defd88cf6a12d559..5265da2d80340e079e12d354030aa8b3f7abecfa 100644 (file)
--- 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)