--- zzzz-none-000/linux-3.10.107/arch/x86/kernel/jump_label.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/arch/x86/kernel/jump_label.c	2021-02-04 17:41:59.000000000 +0000
@@ -24,20 +24,82 @@
 	} __attribute__((packed));
 };
 
+static void bug_at(unsigned char *ip, int line)
+{
+	/*
+	 * The location is not an op that we were expecting.
+	 * Something went wrong. Crash the box, as something could be
+	 * corrupting the kernel.
+	 */
+	pr_warning("Unexpected op at %pS [%p] (%02x %02x %02x %02x %02x) %s:%d\n",
+	       ip, ip, ip[0], ip[1], ip[2], ip[3], ip[4], __FILE__, line);
+	BUG();
+}
+
 static void __jump_label_transform(struct jump_entry *entry,
 				   enum jump_label_type type,
-				   void *(*poker)(void *, const void *, size_t))
+				   void *(*poker)(void *, const void *, size_t),
+				   int init)
 {
 	union jump_code_union code;
+	const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
+	const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
+
+	if (type == JUMP_LABEL_JMP) {
+		if (init) {
+			/*
+			 * Jump label is enabled for the first time.
+			 * So we expect a default_nop...
+			 */
+			if (unlikely(memcmp((void *)entry->code, default_nop, 5)
+				     != 0))
+				bug_at((void *)entry->code, __LINE__);
+		} else {
+			/*
+			 * ...otherwise expect an ideal_nop. Otherwise
+			 * something went horribly wrong.
+			 */
+			if (unlikely(memcmp((void *)entry->code, ideal_nop, 5)
+				     != 0))
+				bug_at((void *)entry->code, __LINE__);
+		}
 
-	if (type == JUMP_LABEL_ENABLE) {
 		code.jump = 0xe9;
 		code.offset = entry->target -
 				(entry->code + JUMP_LABEL_NOP_SIZE);
-	} else
+	} else {
+		/*
+		 * We are disabling this jump label. If it is not what
+		 * we think it is, then something must have gone wrong.
+		 * If this is the first initialization call, then we
+		 * are converting the default nop to the ideal nop.
+		 */
+		if (init) {
+			if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
+				bug_at((void *)entry->code, __LINE__);
+		} else {
+			code.jump = 0xe9;
+			code.offset = entry->target -
+				(entry->code + JUMP_LABEL_NOP_SIZE);
+			if (unlikely(memcmp((void *)entry->code, &code, 5) != 0))
+				bug_at((void *)entry->code, __LINE__);
+		}
 		memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
+	}
 
-	(*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
+	/*
+	 * Make text_poke_bp() a default fallback poker.
+	 *
+	 * At the time the change is being done, just ignore whether we
+	 * are doing nop -> jump or jump -> nop transition, and assume
+	 * always nop being the 'currently valid' instruction
+	 *
+	 */
+	if (poker)
+		(*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
+	else
+		text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE,
+			     (void *)entry->code + JUMP_LABEL_NOP_SIZE);
 }
 
 void arch_jump_label_transform(struct jump_entry *entry,
@@ -45,15 +107,38 @@
 {
 	get_online_cpus();
 	mutex_lock(&text_mutex);
-	__jump_label_transform(entry, type, text_poke_smp);
+	__jump_label_transform(entry, type, NULL, 0);
 	mutex_unlock(&text_mutex);
 	put_online_cpus();
 }
 
+static enum {
+	JL_STATE_START,
+	JL_STATE_NO_UPDATE,
+	JL_STATE_UPDATE,
+} jlstate __initdata_or_module = JL_STATE_START;
+
 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
 				      enum jump_label_type type)
 {
-	__jump_label_transform(entry, type, text_poke_early);
+	/*
+	 * This function is called at boot up and when modules are
+	 * first loaded. Check if the default nop, the one that is
+	 * inserted at compile time, is the ideal nop. If it is, then
+	 * we do not need to update the nop, and we can leave it as is.
+	 * If it is not, then we need to update the nop to the ideal nop.
+	 */
+	if (jlstate == JL_STATE_START) {
+		const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
+		const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
+
+		if (memcmp(ideal_nop, default_nop, 5) != 0)
+			jlstate = JL_STATE_UPDATE;
+		else
+			jlstate = JL_STATE_NO_UPDATE;
+	}
+	if (jlstate == JL_STATE_UPDATE)
+		__jump_label_transform(entry, type, text_poke_early, 1);
 }
 
 #endif