x86/debug: Move cond_local_irq_enable() block into exc_debug_user()

The cond_local_irq_enable() block, dealing with vm86 and sending
signals is only relevant for #DB-from-user, move it there.

This then reduces handle_debug() to only the notifier call, so rename
it to notify_debug().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20200902133201.094265982@infradead.org

Author: Peter Zijlstra

arch/x86/kernel/traps.c

@@ -783,44 +783,20 @@ static __always_inline unsigned long debug_read_clear_dr6(void)
  *
  * May run on IST stack.
  */
-static bool handle_debug(struct pt_regs *regs, unsigned long *dr6)
+
+static bool notify_debug(struct pt_regs *regs, unsigned long *dr6)
 {
 	struct task_struct *tsk = current;
-	bool icebp;
-
-	/*
-	 * If dr6 has no reason to give us about the origin of this trap,
-	 * then it's very likely the result of an icebp/int01 trap.
-	 * User wants a sigtrap for that.
-	 */
-	icebp = !*dr6;
 
 	/* Store the virtualized DR6 value */
 	tsk->thread.debugreg6 = *dr6;
 
 	if (notify_die(DIE_DEBUG, "debug", regs, (long)dr6, 0, SIGTRAP) == NOTIFY_STOP)
 		return true;
 
-	/* It's safe to allow irq's after DR6 has been saved */
-	cond_local_irq_enable(regs);
-
-	if (v8086_mode(regs)) {
-		handle_vm86_trap((struct kernel_vm86_regs *) regs, 0,
-				 X86_TRAP_DB);
-		goto out;
-	}
-
-	/*
-	 * Reload dr6, the notifier might have changed it.
-	 */
+	/* Reload the DR6 value, the notifier might have changed it */
 	*dr6 = tsk->thread.debugreg6;
 
-	if (*dr6 & (DR_STEP | DR_TRAP_BITS) || icebp)
-		send_sigtrap(regs, 0, get_si_code(*dr6));
-
-out:
-	cond_local_irq_disable(regs);
-
 	return false;
 }
 
@@ -864,7 +840,7 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
 	if (!dr6)
 		goto out;
 
-	if (handle_debug(regs, &dr6))
+	if (notify_debug(regs, &dr6))
 		goto out;
 
 	if (WARN_ON_ONCE(dr6 & DR_STEP)) {
@@ -889,6 +865,8 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
 static __always_inline void exc_debug_user(struct pt_regs *regs,
 					   unsigned long dr6)
 {
+	bool icebp;
+
 	/*
 	 * If something gets miswired and we end up here for a kernel mode
 	 * #DB, we will malfunction.
@@ -907,8 +885,30 @@ static __always_inline void exc_debug_user(struct pt_regs *regs,
 	irqentry_enter_from_user_mode(regs);
 	instrumentation_begin();
 
-	handle_debug(regs, &dr6);
+	/*
+	 * If dr6 has no reason to give us about the origin of this trap,
+	 * then it's very likely the result of an icebp/int01 trap.
+	 * User wants a sigtrap for that.
+	 */
+	icebp = !dr6;
+
+	if (notify_debug(regs, &dr6))
+		goto out;
 
+	/* It's safe to allow irq's after DR6 has been saved */
+	local_irq_enable();
+
+	if (v8086_mode(regs)) {
+		handle_vm86_trap((struct kernel_vm86_regs *)regs, 0, X86_TRAP_DB);
+		goto out_irq;
+	}
+
+	if (dr6 & (DR_STEP | DR_TRAP_BITS) || icebp)
+		send_sigtrap(regs, 0, get_si_code(dr6));
+
+out_irq:
+	local_irq_disable();
+out:
 	instrumentation_end();
 	irqentry_exit_to_user_mode(regs);
 }