Revert "kdb: Implement disable_nmi command"

This reverts commit ad394f6.

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/20250129082535.2.Ib91bfb95bdcf77591257a84063fdeb5b4dce65b1@changeid
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: dianders

kernel/debug/kdb/kdb_main.c

@@ -25,7 +25,6 @@
 #include <linux/smp.h>
 #include <linux/utsname.h>
 #include <linux/vmalloc.h>
-#include <linux/atomic.h>
 #include <linux/moduleparam.h>
 #include <linux/mm.h>
 #include <linux/init.h>
@@ -2119,32 +2118,6 @@ static int kdb_dmesg(int argc, const char **argv)
 	return 0;
 }
 #endif /* CONFIG_PRINTK */
-
-/* Make sure we balance enable/disable calls, must disable first. */
-static atomic_t kdb_nmi_disabled;
-
-static int kdb_disable_nmi(int argc, const char *argv[])
-{
-	if (atomic_read(&kdb_nmi_disabled))
-		return 0;
-	atomic_set(&kdb_nmi_disabled, 1);
-	arch_kgdb_ops.enable_nmi(0);
-	return 0;
-}
-
-static int kdb_param_enable_nmi(const char *val, const struct kernel_param *kp)
-{
-	if (!atomic_add_unless(&kdb_nmi_disabled, -1, 0))
-		return -EINVAL;
-	arch_kgdb_ops.enable_nmi(1);
-	return 0;
-}
-
-static const struct kernel_param_ops kdb_param_ops_enable_nmi = {
-	.set = kdb_param_enable_nmi,
-};
-module_param_cb(enable_nmi, &kdb_param_ops_enable_nmi, NULL, 0600);
-
 /*
  * kdb_cpu - This function implements the 'cpu' command.
  *	cpu	[<cpunum>]
@@ -2836,20 +2809,10 @@ static kdbtab_t maintab[] = {
 	},
 };
 
-static kdbtab_t nmicmd = {
-	.name = "disable_nmi",
-	.func = kdb_disable_nmi,
-	.usage = "",
-	.help = "Disable NMI entry to KDB",
-	.flags = KDB_ENABLE_ALWAYS_SAFE,
-};
-
 /* Initialize the kdb command table. */
 static void __init kdb_inittab(void)
 {
 	kdb_register_table(maintab, ARRAY_SIZE(maintab));
-	if (arch_kgdb_ops.enable_nmi)
-		kdb_register_table(&nmicmd, 1);
 }
 
 /* Execute any commands defined in kdb_cmds.  */