diff --git a/kernel/livepatch/state.c b/kernel/livepatch/state.c
new file mode 100644
index 0000000..2565d03
--- /dev/null
+++ b/kernel/livepatch/state.c
@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * system_state.c - State of the system modified by livepatches
+ *
+ * Copyright (C) 2019 SUSE
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/livepatch.h>
+#include "core.h"
+#include "state.h"
+#include "transition.h"
+
+#define klp_for_each_state(patch, state)		\
+	for (state = patch->states; state && state->id; state++)
+
+/**
+ * klp_get_state() - get information about system state modified by
+ *	the given patch
+ * @patch:	livepatch that modifies the given system state
+ * @id:		custom identifier of the modified system state
+ *
+ * Checks whether the given patch modifies the given system state.
+ *
+ * The function can be called either from pre/post (un)patch
+ * callbacks or from the kernel code added by the livepatch.
+ *
+ * Return: pointer to struct klp_state when found, otherwise NULL.
+ */
+struct klp_state *klp_get_state(struct klp_patch *patch, unsigned long id)
+{
+	struct klp_state *state;
+
+	klp_for_each_state(patch, state) {
+		if (state->id == id)
+			return state;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(klp_get_state);
+
+/**
+ * klp_get_prev_state() - get information about system state modified by
+ *	the already installed livepatches
+ * @id:		custom identifier of the modified system state
+ *
+ * Checks whether already installed livepatches modify the given
+ * system state.
+ *
+ * The same system state can be modified by more non-cumulative
+ * livepatches. It is expected that the latest livepatch has
+ * the most up-to-date information.
+ *
+ * The function can be called only during transition when a new
+ * livepatch is being enabled or when such a transition is reverted.
+ * It is typically called only from pre/post (un)patch
+ * callbacks.
+ *
+ * Return: pointer to the latest struct klp_state from already
+ *	installed livepatches, NULL when not found.
+ */
+struct klp_state *klp_get_prev_state(unsigned long id)
+{
+	struct klp_patch *patch;
+	struct klp_state *state, *last_state = NULL;
+
+	if (WARN_ON_ONCE(!klp_transition_patch))
+		return NULL;
+
+	klp_for_each_patch(patch) {
+		if (patch == klp_transition_patch)
+			goto out;
+
+		state = klp_get_state(patch, id);
+		if (state)
+			last_state = state;
+	}
+
+out:
+	return last_state;
+}
+EXPORT_SYMBOL_GPL(klp_get_prev_state);
+
+/* Check if the patch is able to deal with the existing system state. */
+static bool klp_is_state_compatible(struct klp_patch *patch,
+				    struct klp_state *old_state)
+{
+	struct klp_state *state;
+
+	state = klp_get_state(patch, old_state->id);
+
+	/* A cumulative livepatch must handle all already modified states. */
+	if (!state)
+		return !patch->replace;
+
+	return state->version >= old_state->version;
+}
+
+/*
+ * Check that the new livepatch will not break the existing system states.
+ * Cumulative patches must handle all already modified states.
+ * Non-cumulative patches can touch already modified states.
+ */
+bool klp_is_patch_compatible(struct klp_patch *patch)
+{
+	struct klp_patch *old_patch;
+	struct klp_state *old_state;
+
+	klp_for_each_patch(old_patch) {
+		klp_for_each_state(old_patch, old_state) {
+			if (!klp_is_state_compatible(patch, old_state))
+				return false;
+		}
+	}
+
+	return true;
+}