[patch 08/16] x86/entry: Implement user mode C entry points for #DB and #MCE

[Thomas Gleixner <tglx@linutronix.de>]

The MCE entry point uses the same mechanism as the IST entry point for
now. For #DB split the inner workings and just keep the ist_enter/exit
magic in the IST variant. Fixup the ASM code to emit the proper
noist_##cfunc call.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/entry/entry_64.S      |    2 +-
 arch/x86/kernel/cpu/mce/core.c |   11 +++++++++++
 arch/x86/kernel/traps.c        |   30 ++++++++++++++++++++++--------
 3 files changed, 34 insertions(+), 9 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -646,7 +646,7 @@ SYM_CODE_START(\asmsym)
 
 	/* Switch to the regular task stack and use the noist entry point */
 .Lfrom_usermode_switch_stack_\@:
-	idtentry_body vector \cfunc, has_error_code=0
+	idtentry_body vector noist_\cfunc, has_error_code=0
 
 _ASM_NOKPROBE(\asmsym)
 SYM_CODE_END(\asmsym)
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1898,11 +1898,22 @@ static void unexpected_machine_check(str
 /* Call the installed machine check handler for this CPU setup. */
 void (*machine_check_vector)(struct pt_regs *) = unexpected_machine_check;
 
+/* MCE hit kernel mode */
 DEFINE_IDTENTRY_MCE(exc_machine_check)
 {
 	machine_check_vector(regs);
 }
 
+#ifdef CONFIG_X86_64
+/*
+ * The user mode variant (same content for now).
+ */
+DEFINE_IDTENTRY_MCE_USER(exc_machine_check)
+{
+	machine_check_vector(regs);
+}
+#endif
+
 /*
  * Called for each booted CPU to set up machine checks.
  * Must be called with preempt off:
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -739,15 +739,13 @@ static bool is_sysenter_singlestep(struc
  *
  * May run on IST stack.
  */
-DEFINE_IDTENTRY_DEBUG(exc_debug)
+static void notrace handle_debug(struct pt_regs *regs)
 {
 	struct task_struct *tsk = current;
 	int user_icebp = 0;
 	unsigned long dr6;
 	int si_code;
 
-	ist_enter(regs);
-
 	get_debugreg(dr6, 6);
 	/*
 	 * The Intel SDM says:
@@ -776,7 +774,7 @@ DEFINE_IDTENTRY_DEBUG(exc_debug)
 		     is_sysenter_singlestep(regs))) {
 		dr6 &= ~DR_STEP;
 		if (!dr6)
-			goto exit;
+			return;
 		/*
 		 * else we might have gotten a single-step trap and hit a
 		 * watchpoint at the same time, in which case we should fall
@@ -797,12 +795,12 @@ DEFINE_IDTENTRY_DEBUG(exc_debug)
 
 #ifdef CONFIG_KPROBES
 	if (kprobe_debug_handler(regs))
-		goto exit;
+		return;
 #endif
 
 	if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, 0,
 		       SIGTRAP) == NOTIFY_STOP)
-		goto exit;
+		return;
 
 	/*
 	 * Let others (NMI) know that the debug stack is in use
@@ -818,7 +816,7 @@ DEFINE_IDTENTRY_DEBUG(exc_debug)
 				 X86_TRAP_DB);
 		cond_local_irq_disable(regs);
 		debug_stack_usage_dec();
-		goto exit;
+		return;
 	}
 
 	if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) {
@@ -837,11 +835,27 @@ DEFINE_IDTENTRY_DEBUG(exc_debug)
 		send_sigtrap(regs, 0, si_code);
 	cond_local_irq_disable(regs);
 	debug_stack_usage_dec();
+}
+NOKPROBE_SYMBOL(handle_debug);
 
-exit:
+/*
+ * IST stack entry.
+ */
+DEFINE_IDTENTRY_DEBUG(exc_debug)
+{
+	ist_enter(regs);
+	handle_debug(regs);
 	ist_exit(regs);
 }
 
+#ifdef CONFIG_X86_64
+/* User entry, runs on regular task stack */
+DEFINE_IDTENTRY_DEBUG_USER(exc_debug)
+{
+	handle_debug(regs);
+}
+#endif
+
 /*
  * Note that we play around with the 'TS' bit in an attempt to get
  * the correct behaviour even in the presence of the asynchronous