powerpc/xmon: Clear all breakpoints when xmon is disabled via debugfs

Presently when xmon is disabled by debugfs any existing
instruction/data-access breakpoints set are not disabled. This may
lead to kernel oops when those breakpoints are hit as the necessary
debugger hooks aren't installed.

Hence this patch introduces a new function named clear_all_bpt() which
is called when xmon is disabled via debugfs. The function will
unpatch/clear all the trap and ciabr/dab based breakpoints.
Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Reviewed-by: Balbir Singh <bsingharora@gmail.com>
[mpe: Fix build break when CONFIG_DEBUG_FS=n]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/xmon/xmon.c

@@ -3664,11 +3664,35 @@ device_initcall(setup_xmon_sysrq);
 #endif /* CONFIG_MAGIC_SYSRQ */
 
 #ifdef CONFIG_DEBUG_FS
+static void clear_all_bpt(void)
+{
+	int i;
+
+	/* clear/unpatch all breakpoints */
+	remove_bpts();
+	remove_cpu_bpts();
+
+	/* Disable all breakpoints */
+	for (i = 0; i < NBPTS; ++i)
+		bpts[i].enabled = 0;
+
+	/* Clear any data or iabr breakpoints */
+	if (iabr || dabr.enabled) {
+		iabr = NULL;
+		dabr.enabled = 0;
+	}
+
+	printf("xmon: All breakpoints cleared\n");
+}
+
 static int xmon_dbgfs_set(void *data, u64 val)
 {
 	xmon_on = !!val;
 	xmon_init(xmon_on);
 
+	/* make sure all breakpoints removed when disabling */
+	if (!xmon_on)
+		clear_all_bpt();
 	return 0;
 }