arm64: debug: refactor reinstall_suspended_bps()

`reinstall_suspended_bps()` plays a key part in the stepping process
when we have hardware breakpoints and watchpoints enabled.
It checks if we need to step one, will re-enable it if it has
been handled and will return whether or not we need to proceed with
a single-step.

However, the current naming and return values make it harder to understand
the logic and goal of the function.

Rename it `try_step_suspended_breakpoints()` and change the return value
to a boolean, aligning it with similar functions used in
`do_el0_undef()` like `try_emulate_mrs()`, and making its behaviour
more obvious.

Signed-off-by: Ada Couprie Diaz <[email protected]>
Tested-by: Luis Claudio R. Goncalves <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Reviewed-by: Will Deacon <[email protected]>
Acked-by: Mark Rutland <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: Ada Couprie Diaz

arch/arm64/include/asm/debug-monitors.h

@@ -84,11 +84,11 @@ void kernel_rewind_single_step(struct pt_regs *regs);
 void kernel_fastforward_single_step(struct pt_regs *regs);
 
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
-int reinstall_suspended_bps(struct pt_regs *regs);
+bool try_step_suspended_breakpoints(struct pt_regs *regs);
 #else
-static inline int reinstall_suspended_bps(struct pt_regs *regs)
+static inline bool try_step_suspended_breakpoints(struct pt_regs *regs)
 {
-	return -ENODEV;
+	return false;
 }
 #endif
 

arch/arm64/kernel/debug-monitors.c

@@ -195,7 +195,7 @@ static int single_step_handler(unsigned long unused, unsigned long esr,
 	 * If we are stepping a pending breakpoint, call the hw_breakpoint
 	 * handler first.
 	 */
-	if (!reinstall_suspended_bps(regs))
+	if (try_step_suspended_breakpoints(regs))
 		return 0;
 
 	if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)

arch/arm64/kernel/hw_breakpoint.c

@@ -847,36 +847,35 @@ NOKPROBE_SYMBOL(watchpoint_handler);
 /*
  * Handle single-step exception.
  */
-int reinstall_suspended_bps(struct pt_regs *regs)
+bool try_step_suspended_breakpoints(struct pt_regs *regs)
 {
 	struct debug_info *debug_info = &current->thread.debug;
-	int handled_exception = 0, *kernel_step;
-
-	kernel_step = this_cpu_ptr(&stepping_kernel_bp);
+	int *kernel_step = this_cpu_ptr(&stepping_kernel_bp);
+	bool handled_exception = false;
 
 	/*
 	 * Called from single-step exception handler.
-	 * Return 0 if execution can resume, 1 if a SIGTRAP should be
-	 * reported.
+	 * Return true if we stepped a breakpoint and can resume execution,
+	 * false if we need to handle a single-step.
 	 */
 	if (user_mode(regs)) {
 		if (debug_info->bps_disabled) {
 			debug_info->bps_disabled = 0;
 			toggle_bp_registers(AARCH64_DBG_REG_BCR, DBG_ACTIVE_EL0, 1);
-			handled_exception = 1;
+			handled_exception = true;
 		}
 
 		if (debug_info->wps_disabled) {
 			debug_info->wps_disabled = 0;
 			toggle_bp_registers(AARCH64_DBG_REG_WCR, DBG_ACTIVE_EL0, 1);
-			handled_exception = 1;
+			handled_exception = true;
 		}
 
 		if (handled_exception) {
 			if (debug_info->suspended_step) {
 				debug_info->suspended_step = 0;
 				/* Allow exception handling to fall-through. */
-				handled_exception = 0;
+				handled_exception = false;
 			} else {
 				user_disable_single_step(current);
 			}
@@ -890,17 +889,17 @@ int reinstall_suspended_bps(struct pt_regs *regs)
 
 		if (*kernel_step != ARM_KERNEL_STEP_SUSPEND) {
 			kernel_disable_single_step();
-			handled_exception = 1;
+			handled_exception = true;
 		} else {
-			handled_exception = 0;
+			handled_exception = false;
 		}
 
 		*kernel_step = ARM_KERNEL_STEP_NONE;
 	}
 
-	return !handled_exception;
+	return handled_exception;
 }
-NOKPROBE_SYMBOL(reinstall_suspended_bps);
+NOKPROBE_SYMBOL(try_step_suspended_breakpoints);
 
 /*
  * Context-switcher for restoring suspended breakpoints.