Message-ID: <20250515182322.117840-6-pasha.tatashin@soleen.com>
Date: Thu, 15 May 2025 18:23:09 +0000
From: Pasha Tatashin <pasha.tatashin@...een.com>
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Subject: [RFC v2 05/16] luo: luo_core: integrate with KHO

Integrate the LUO with the KHO framework to enable passing LUO state
across a kexec reboot.

This patch introduces the following changes:
- During the KHO finalization phase allocate FDT blob.
- Populate this FDT with a LUO compatibility string ("luo-v1") and the
  current LUO state (`luo_state`).
- Implement a KHO notifier

LUO now depends on `CONFIG_KEXEC_HANDOVER`. The core state transition
logic (`luo_do_*_calls`) remains unimplemented in this patch.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 drivers/misc/liveupdate/luo_core.c | 222 ++++++++++++++++++++++++++++-
 1 file changed, 219 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/liveupdate/luo_core.c b/drivers/misc/liveupdate/luo_core.c
index 919c37b0b4d1..a76e886bc3b1 100644
--- a/drivers/misc/liveupdate/luo_core.c
+++ b/drivers/misc/liveupdate/luo_core.c
@@ -36,9 +36,12 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/err.h>
+#include <linux/kexec_handover.h>
 #include <linux/kobject.h>
+#include <linux/libfdt.h>
 #include <linux/liveupdate.h>
 #include <linux/rwsem.h>
+#include <linux/sizes.h>
 #include <linux/string.h>
 #include "luo_internal.h"
 
@@ -55,6 +58,12 @@ const char *const luo_state_str[] = {
 
 bool luo_enabled;
 
+static void *luo_fdt_out;
+static void *luo_fdt_in;
+#define LUO_FDT_SIZE		SZ_1M
+#define LUO_KHO_ENTRY_NAME	"LUO"
+#define LUO_COMPATIBLE		"luo-v1"
+
 static int __init early_liveupdate_param(char *buf)
 {
 	return kstrtobool(buf, &luo_enabled);
@@ -79,6 +88,60 @@ static inline void luo_set_state(enum liveupdate_state state)
 	__luo_set_state(state);
 }
 
+/* Called during the prepare phase, to create LUO fdt tree */
+static int luo_fdt_setup(struct kho_serialization *ser)
+{
+	void *fdt_out;
+	int ret;
+
+	fdt_out = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
+					   get_order(LUO_FDT_SIZE));
+	if (!fdt_out) {
+		pr_err("failed to allocate FDT memory\n");
+		return -ENOMEM;
+	}
+
+	ret = fdt_create_empty_tree(fdt_out, LUO_FDT_SIZE);
+	if (ret)
+		goto exit_free;
+
+	ret = fdt_setprop(fdt_out, 0, "compatible", LUO_COMPATIBLE,
+			  strlen(LUO_COMPATIBLE) + 1);
+	if (ret)
+		goto exit_free;
+
+	ret = kho_preserve_phys(__pa(fdt_out), LUO_FDT_SIZE);
+	if (ret)
+		goto exit_free;
+
+	ret = kho_add_subtree(ser, LUO_KHO_ENTRY_NAME, fdt_out);
+	if (ret)
+		goto exit_unpreserve;
+	luo_fdt_out = fdt_out;
+
+	return 0;
+
+exit_unpreserve:
+	kho_unpreserve_phys(__pa(fdt_out), LUO_FDT_SIZE);
+exit_free:
+	free_pages((unsigned long)fdt_out, get_order(LUO_FDT_SIZE));
+	pr_err("failed to prepare LUO FDT: %d\n", ret);
+
+	return ret;
+}
+
+static void luo_fdt_destroy(void)
+{
+	kho_unpreserve_phys(__pa(luo_fdt_out), LUO_FDT_SIZE);
+	free_pages((unsigned long)luo_fdt_out, get_order(LUO_FDT_SIZE));
+	luo_fdt_out = NULL;
+}
+
+static int luo_do_prepare_calls(void)
+{
+	return 0;
+}
+
 static int luo_do_freeze_calls(void)
 {
 	return 0;
@@ -88,11 +151,111 @@ static void luo_do_finish_calls(void)
 {
 }
 
-int luo_prepare(void)
+static void luo_do_cancel_calls(void)
+{
+}
+
+static int __luo_prepare(struct kho_serialization *ser)
 {
+	int ret;
+
+	if (down_write_killable(&luo_state_rwsem)) {
+		pr_warn("[prepare] event canceled by user\n");
+		return -EAGAIN;
+	}
+
+	if (!is_current_luo_state(LIVEUPDATE_STATE_NORMAL)) {
+		pr_warn("Can't switch to [%s] from [%s] state\n",
+			luo_state_str[LIVEUPDATE_STATE_PREPARED],
+			LUO_STATE_STR);
+		ret = -EINVAL;
+		goto exit_unlock;
+	}
+
+	ret = luo_fdt_setup(ser);
+	if (ret)
+		goto exit_unlock;
+
+	ret = luo_do_prepare_calls();
+	if (ret)
+		goto exit_unlock;
+
+	luo_set_state(LIVEUPDATE_STATE_PREPARED);
+
+exit_unlock:
+	up_write(&luo_state_rwsem);
+
+	return ret;
+}
+
+static int __luo_cancel(void)
+{
+	if (down_write_killable(&luo_state_rwsem)) {
+		pr_warn("[cancel] event canceled by user\n");
+		return -EAGAIN;
+	}
+
+	if (!is_current_luo_state(LIVEUPDATE_STATE_PREPARED) &&
+	    !is_current_luo_state(LIVEUPDATE_STATE_FROZEN)) {
+		pr_warn("Can't switch to [%s] from [%s] state\n",
+			luo_state_str[LIVEUPDATE_STATE_NORMAL],
+			LUO_STATE_STR);
+		up_write(&luo_state_rwsem);
+
+		return -EINVAL;
+	}
+
+	luo_do_cancel_calls();
+	luo_fdt_destroy();
+	luo_set_state(LIVEUPDATE_STATE_NORMAL);
+
+	up_write(&luo_state_rwsem);
+
 	return 0;
 }
 
+static int luo_kho_notifier(struct notifier_block *self,
+			    unsigned long cmd, void *v)
+{
+	int ret;
+
+	switch (cmd) {
+	case KEXEC_KHO_FINALIZE:
+		ret = __luo_prepare((struct kho_serialization *)v);
+		break;
+	case KEXEC_KHO_ABORT:
+		ret = __luo_cancel();
+		break;
+	default:
+		return NOTIFY_BAD;
+	}
+
+	return notifier_from_errno(ret);
+}
+
+static struct notifier_block luo_kho_notifier_nb = {
+	.notifier_call = luo_kho_notifier,
+};
+
+/**
+ * luo_prepare - Initiate the live update preparation phase.
+ *
+ * This function is called to begin the live update process. It attempts to
+ * transition the luo to the ``LIVEUPDATE_STATE_PREPARED`` state.
+ *
+ * If the calls complete successfully, the orchestrator state is set
+ * to ``LIVEUPDATE_STATE_PREPARED``. If any  call fails a
+ * ``LIVEUPDATE_CANCEL`` is sent to roll back any actions.
+ *
+ * @return 0 on success, ``-EAGAIN`` if the state change was cancelled by the
+ * user while waiting for the lock, ``-EINVAL`` if the orchestrator is not in
+ * the normal state, or a negative error code returned by the calls.
+ */
+int luo_prepare(void)
+{
+	return kho_finalize();
+}
+
 /**
  * luo_freeze() - Initiate the final freeze notification phase for live update.
  *
@@ -188,9 +351,23 @@ int luo_finish(void)
 	return 0;
 }
 
+/**
+ * luo_cancel - Cancel the ongoing live update from prepared or frozen states.
+ *
+ * This function is called to abort a live update that is currently in the
+ * ``LIVEUPDATE_STATE_PREPARED`` state.
+ *
+ * If the state is correct, it triggers the ``LIVEUPDATE_CANCEL`` notifier chain
+ * to allow subsystems to undo any actions performed during the prepare or
+ * freeze events. Finally, the orchestrator state is transitioned back to
+ * ``LIVEUPDATE_STATE_NORMAL``.
+ *
+ * @return 0 on success, or ``-EAGAIN`` if the state change was cancelled by the
+ * user while waiting for the lock.
+ */
 int luo_cancel(void)
 {
-	return 0;
+	return kho_abort();
 }
 
 void luo_state_read_enter(void)
@@ -205,7 +382,46 @@ void luo_state_read_exit(void)
 
 static int __init luo_startup(void)
 {
-	__luo_set_state(LIVEUPDATE_STATE_NORMAL);
+	phys_addr_t fdt_phys;
+	int ret;
+
+	if (!kho_is_enabled()) {
+		if (luo_enabled)
+			pr_warn("Disabling liveupdate because KHO is disabled\n");
+		luo_enabled = false;
+		return 0;
+	}
+
+	ret = register_kho_notifier(&luo_kho_notifier_nb);
+	if (ret) {
+		luo_enabled = false;
+		pr_warn("Failed to register with KHO [%d]\n", ret);
+	}
+
+	/*
+	 * Retrieve LUO subtree, and verify its format.  Panic in case of
+	 * exceptions, since machine devices and memory is in unpredictable
+	 * state.
+	 */
+	ret = kho_retrieve_subtree(LUO_KHO_ENTRY_NAME, &fdt_phys);
+	if (ret) {
+		if (ret != -ENOENT) {
+			panic("failed to retrieve FDT '%s' from KHO: %d\n",
+			      LUO_KHO_ENTRY_NAME, ret);
+		}
+		__luo_set_state(LIVEUPDATE_STATE_NORMAL);
+
+		return 0;
+	}
+
+	luo_fdt_in = __va(fdt_phys);
+	ret = fdt_node_check_compatible(luo_fdt_in, 0, LUO_COMPATIBLE);
+	if (ret) {
+		panic("FDT '%s' is incompatible with '%s' [%d]\n",
+		      LUO_KHO_ENTRY_NAME, LUO_COMPATIBLE, ret);
+	}
+
+	__luo_set_state(LIVEUPDATE_STATE_UPDATED);
 
 	return 0;
 }
-- 
2.49.0.1101.gccaa498523-goog

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