Revert "kernel/debug: Mask KGDB NMI upon entry"

This reverts commit 5a14fea.

No architectures ever implemented `enable_nmi` since the later patches
in the series adding it never landed. It's been a long time. Drop it.

NOTE: this is not a clean revert due to changes in the file in the
meantime.

Signed-off-by: Douglas Anderson <[email protected]>
Link: https://lore.kernel.org/r/20250129082535.3.I2254953cd852f31f354456689d68b2d910de3fbe@changeid
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: dianders

include/linux/kgdb.h

@@ -257,7 +257,6 @@ extern void kgdb_arch_late(void);
  * hardware breakpoints.
  * @correct_hw_break: Allow an architecture to specify how to correct the
  * hardware debug registers.
- * @enable_nmi: Manage NMI-triggered entry to KGDB
  */
 struct kgdb_arch {
 	unsigned char		gdb_bpt_instr[BREAK_INSTR_SIZE];
@@ -270,8 +269,6 @@ struct kgdb_arch {
 	void	(*disable_hw_break)(struct pt_regs *regs);
 	void	(*remove_all_hw_break)(void);
 	void	(*correct_hw_break)(void);
-
-	void	(*enable_nmi)(bool on);
 };
 
 /**

kernel/debug/debug_core.c

@@ -837,10 +837,6 @@ kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 {
 	struct kgdb_state kgdb_var;
 	struct kgdb_state *ks = &kgdb_var;
-	int ret = 0;
-
-	if (arch_kgdb_ops.enable_nmi)
-		arch_kgdb_ops.enable_nmi(0);
 	/*
 	 * Avoid entering the debugger if we were triggered due to an oops
 	 * but panic_timeout indicates the system should automatically
@@ -858,15 +854,11 @@ kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 	ks->linux_regs		= regs;
 
 	if (kgdb_reenter_check(ks))
-		goto out; /* Ouch, double exception ! */
+		return 0; /* Ouch, double exception ! */
 	if (kgdb_info[ks->cpu].enter_kgdb != 0)
-		goto out;
+		return 0;
 
-	ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
-out:
-	if (arch_kgdb_ops.enable_nmi)
-		arch_kgdb_ops.enable_nmi(1);
-	return ret;
+	return kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 }
 NOKPROBE_SYMBOL(kgdb_handle_exception);