+ kho-make-debugfs-interface-optional.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: kho: make debugfs interface optional
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     kho-make-debugfs-interface-optional.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kho-make-debugfs-interface-optional.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Pasha Tatashin <pasha.tatashin@soleen.com>
Subject: kho: make debugfs interface optional
Date: Sat, 1 Nov 2025 10:23:17 -0400

Patch series "liveupdate: Rework KHO for in-kernel users", v9.

This series refactors the KHO framework to better support in-kernel users
like the upcoming LUO.  The current design, which relies on a notifier
chain and debugfs for control, is too restrictive for direct programmatic
use.

The core of this rework is the removal of the notifier chain in favor of a
direct registration API.  This decouples clients from the shutdown-time
finalization sequence, allowing them to manage their preserved state more
flexibly and at any time.

In support of this new model, this series also:
 - Makes the debugfs interface optional.
 - Introduces APIs to unpreserve memory and fixes a bug in the abort
   path where client state was being incorrectly discarded. Note that
   this is an interim step, as a more comprehensive fix is planned as
   part of the stateless KHO work [1].
 - Moves all KHO code into a new kernel/liveupdate/ directory to
   consolidate live update components.


This patch (of 9):

Currently, KHO is controlled via debugfs interface, but once LUO is
introduced, it can control KHO, and the debug interface becomes optional.

Add a separate config CONFIG_KEXEC_HANDOVER_DEBUGFS that enables the
debugfs interface, and allows to inspect the tree.

Move all debugfs related code to a new file to keep the .c files clear of
ifdefs.

Link: https://lkml.kernel.org/r/20251101142325.1326536-1-pasha.tatashin@soleen.com
Link: https://lkml.kernel.org/r/20251101142325.1326536-2-pasha.tatashin@soleen.com
Link: https://lore.kernel.org/all/20251020100306.2709352-1-jasonmiu@google.com [1]
Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 MAINTAINERS                           |    2 
 kernel/Kconfig.kexec                  |   12 -
 kernel/Makefile                       |    1 
 kernel/kexec_handover.c               |  273 ++++--------------------
 kernel/kexec_handover_debugfs.c       |  216 ++++++++++++++++++
 kernel/kexec_handover_internal.h      |   39 +++
 tools/testing/selftests/kho/vmtest.sh |    1 
 7 files changed, 320 insertions(+), 224 deletions(-)

--- a/kernel/Kconfig.kexec~kho-make-debugfs-interface-optional
+++ a/kernel/Kconfig.kexec
@@ -100,7 +100,6 @@ config KEXEC_HANDOVER
 	depends on !DEFERRED_STRUCT_PAGE_INIT
 	select MEMBLOCK_KHO_SCRATCH
 	select KEXEC_FILE
-	select DEBUG_FS
 	select LIBFDT
 	select CMA
 	help
@@ -118,6 +117,17 @@ config KEXEC_HANDOVER_DEBUG
 	  scenarios and the extra code might be adding overhead it is
 	  only optionally enabled.
 
+config KEXEC_HANDOVER_DEBUGFS
+	bool "kexec handover debugfs interface"
+	default KEXEC_HANDOVER
+	depends on KEXEC_HANDOVER
+	select DEBUG_FS
+	help
+	  Allow to control kexec handover device tree via debugfs
+	  interface, i.e. finalize the state or aborting the finalization.
+	  Also, enables inspecting the KHO fdt trees with the debugfs binary
+	  blobs.
+
 config CRASH_DUMP
 	bool "kernel crash dumps"
 	default ARCH_DEFAULT_CRASH_DUMP
--- a/kernel/kexec_handover.c~kho-make-debugfs-interface-optional
+++ a/kernel/kexec_handover.c
@@ -11,7 +11,6 @@
 #include <linux/cleanup.h>
 #include <linux/cma.h>
 #include <linux/count_zeros.h>
-#include <linux/debugfs.h>
 #include <linux/kexec.h>
 #include <linux/kexec_handover.h>
 #include <linux/libfdt.h>
@@ -30,6 +29,7 @@
  */
 #include "../mm/internal.h"
 #include "kexec_internal.h"
+#include "kexec_handover_internal.h"
 
 #define KHO_FDT_COMPATIBLE "kho-v1"
 #define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
@@ -105,8 +105,6 @@ struct khoser_mem_chunk;
 
 struct kho_serialization {
 	struct page *fdt;
-	struct list_head fdt_list;
-	struct dentry *sub_fdt_dir;
 	struct kho_mem_track track;
 	/* First chunk of serialized preserved memory map */
 	struct khoser_mem_chunk *preserved_mem_map;
@@ -114,20 +112,16 @@ struct kho_serialization {
 
 struct kho_out {
 	struct blocking_notifier_head chain_head;
-
-	struct dentry *dir;
-
 	struct mutex lock; /* protects KHO FDT finalization */
-
 	struct kho_serialization ser;
 	bool finalized;
+	struct kho_debugfs dbg;
 };
 
 static struct kho_out kho_out = {
 	.chain_head = BLOCKING_NOTIFIER_INIT(kho_out.chain_head),
 	.lock = __MUTEX_INITIALIZER(kho_out.lock),
 	.ser = {
-		.fdt_list = LIST_HEAD_INIT(kho_out.ser.fdt_list),
 		.track = {
 			.orders = XARRAY_INIT(kho_out.ser.track.orders, 0),
 		},
@@ -477,8 +471,8 @@ static void __init kho_mem_deserialize(c
  * area for early allocations that happen before page allocator is
  * initialized.
  */
-static struct kho_scratch *kho_scratch;
-static unsigned int kho_scratch_cnt;
+struct kho_scratch *kho_scratch;
+unsigned int kho_scratch_cnt;
 
 /*
  * The scratch areas are scaled by default as percent of memory allocated from
@@ -674,37 +668,6 @@ err_disable_kho:
 	kho_enable = false;
 }
 
-struct fdt_debugfs {
-	struct list_head list;
-	struct debugfs_blob_wrapper wrapper;
-	struct dentry *file;
-};
-
-static int kho_debugfs_fdt_add(struct list_head *list, struct dentry *dir,
-			       const char *name, const void *fdt)
-{
-	struct fdt_debugfs *f;
-	struct dentry *file;
-
-	f = kmalloc(sizeof(*f), GFP_KERNEL);
-	if (!f)
-		return -ENOMEM;
-
-	f->wrapper.data = (void *)fdt;
-	f->wrapper.size = fdt_totalsize(fdt);
-
-	file = debugfs_create_blob(name, 0400, dir, &f->wrapper);
-	if (IS_ERR(file)) {
-		kfree(f);
-		return PTR_ERR(file);
-	}
-
-	f->file = file;
-	list_add(&f->list, list);
-
-	return 0;
-}
-
 /**
  * kho_add_subtree - record the physical address of a sub FDT in KHO root tree.
  * @ser: serialization control object passed by KHO notifiers.
@@ -716,7 +679,8 @@ static int kho_debugfs_fdt_add(struct li
  * by KHO for the new kernel to retrieve it after kexec.
  *
  * A debugfs blob entry is also created at
- * ``/sys/kernel/debug/kho/out/sub_fdts/@name``.
+ * ``/sys/kernel/debug/kho/out/sub_fdts/@name`` when kernel is configured with
+ * CONFIG_KEXEC_HANDOVER_DEBUGFS
  *
  * Return: 0 on success, error code on failure
  */
@@ -733,7 +697,7 @@ int kho_add_subtree(struct kho_serializa
 	if (err)
 		return err;
 
-	return kho_debugfs_fdt_add(&ser->fdt_list, ser->sub_fdt_dir, name, fdt);
+	return kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);
 }
 EXPORT_SYMBOL_GPL(kho_add_subtree);
 
@@ -1065,30 +1029,7 @@ err_free_pages_array:
 }
 EXPORT_SYMBOL_GPL(kho_restore_vmalloc);
 
-/* Handling for debug/kho/out */
-
-static struct dentry *debugfs_root;
-
-static int kho_out_update_debugfs_fdt(void)
-{
-	int err = 0;
-	struct fdt_debugfs *ff, *tmp;
-
-	if (kho_out.finalized) {
-		err = kho_debugfs_fdt_add(&kho_out.ser.fdt_list, kho_out.dir,
-					  "fdt", page_to_virt(kho_out.ser.fdt));
-	} else {
-		list_for_each_entry_safe(ff, tmp, &kho_out.ser.fdt_list, list) {
-			debugfs_remove(ff->file);
-			list_del(&ff->list);
-			kfree(ff);
-		}
-	}
-
-	return err;
-}
-
-static int kho_abort(void)
+static int __kho_abort(void)
 {
 	int err;
 	unsigned long order;
@@ -1121,7 +1062,28 @@ static int kho_abort(void)
 	return err;
 }
 
-static int kho_finalize(void)
+int kho_abort(void)
+{
+	int ret = 0;
+
+	if (!kho_enable)
+		return -EOPNOTSUPP;
+
+	guard(mutex)(&kho_out.lock);
+	if (!kho_out.finalized)
+		return -ENOENT;
+
+	ret = __kho_abort();
+	if (ret)
+		return ret;
+
+	kho_out.finalized = false;
+	kho_debugfs_cleanup(&kho_out.dbg);
+
+	return 0;
+}
+
+static int __kho_finalize(void)
 {
 	int err = 0;
 	u64 *preserved_mem_map;
@@ -1164,118 +1126,46 @@ static int kho_finalize(void)
 abort:
 	if (err) {
 		pr_err("Failed to convert KHO state tree: %d\n", err);
-		kho_abort();
+		__kho_abort();
 	}
 
 	return err;
 }
 
-static int kho_out_finalize_get(void *data, u64 *val)
+int kho_finalize(void)
 {
-	mutex_lock(&kho_out.lock);
-	*val = kho_out.finalized;
-	mutex_unlock(&kho_out.lock);
-
-	return 0;
-}
+	int ret;
 
-static int kho_out_finalize_set(void *data, u64 _val)
-{
-	int ret = 0;
-	bool val = !!_val;
-
-	mutex_lock(&kho_out.lock);
+	if (!kho_enable)
+		return -EOPNOTSUPP;
 
-	if (val == kho_out.finalized) {
-		if (kho_out.finalized)
-			ret = -EEXIST;
-		else
-			ret = -ENOENT;
-		goto unlock;
-	}
-
-	if (val)
-		ret = kho_finalize();
-	else
-		ret = kho_abort();
+	guard(mutex)(&kho_out.lock);
+	if (kho_out.finalized)
+		return -EEXIST;
 
+	ret = __kho_finalize();
 	if (ret)
-		goto unlock;
-
-	kho_out.finalized = val;
-	ret = kho_out_update_debugfs_fdt();
-
-unlock:
-	mutex_unlock(&kho_out.lock);
-	return ret;
-}
-
-DEFINE_DEBUGFS_ATTRIBUTE(fops_kho_out_finalize, kho_out_finalize_get,
-			 kho_out_finalize_set, "%llu\n");
-
-static int scratch_phys_show(struct seq_file *m, void *v)
-{
-	for (int i = 0; i < kho_scratch_cnt; i++)
-		seq_printf(m, "0x%llx\n", kho_scratch[i].addr);
-
-	return 0;
-}
-DEFINE_SHOW_ATTRIBUTE(scratch_phys);
+		return ret;
 
-static int scratch_len_show(struct seq_file *m, void *v)
-{
-	for (int i = 0; i < kho_scratch_cnt; i++)
-		seq_printf(m, "0x%llx\n", kho_scratch[i].size);
+	kho_out.finalized = true;
 
-	return 0;
+	return kho_debugfs_fdt_add(&kho_out.dbg, "fdt",
+				   page_to_virt(kho_out.ser.fdt), true);
 }
-DEFINE_SHOW_ATTRIBUTE(scratch_len);
 
-static __init int kho_out_debugfs_init(void)
+bool kho_finalized(void)
 {
-	struct dentry *dir, *f, *sub_fdt_dir;
-
-	dir = debugfs_create_dir("out", debugfs_root);
-	if (IS_ERR(dir))
-		return -ENOMEM;
-
-	sub_fdt_dir = debugfs_create_dir("sub_fdts", dir);
-	if (IS_ERR(sub_fdt_dir))
-		goto err_rmdir;
-
-	f = debugfs_create_file("scratch_phys", 0400, dir, NULL,
-				&scratch_phys_fops);
-	if (IS_ERR(f))
-		goto err_rmdir;
-
-	f = debugfs_create_file("scratch_len", 0400, dir, NULL,
-				&scratch_len_fops);
-	if (IS_ERR(f))
-		goto err_rmdir;
-
-	f = debugfs_create_file("finalize", 0600, dir, NULL,
-				&fops_kho_out_finalize);
-	if (IS_ERR(f))
-		goto err_rmdir;
-
-	kho_out.dir = dir;
-	kho_out.ser.sub_fdt_dir = sub_fdt_dir;
-	return 0;
-
-err_rmdir:
-	debugfs_remove_recursive(dir);
-	return -ENOENT;
+	guard(mutex)(&kho_out.lock);
+	return kho_out.finalized;
 }
 
 struct kho_in {
-	struct dentry *dir;
 	phys_addr_t fdt_phys;
 	phys_addr_t scratch_phys;
-	struct list_head fdt_list;
+	struct kho_debugfs dbg;
 };
 
 static struct kho_in kho_in = {
-	.fdt_list = LIST_HEAD_INIT(kho_in.fdt_list),
 };
 
 static const void *kho_get_fdt(void)
@@ -1339,56 +1229,6 @@ int kho_retrieve_subtree(const char *nam
 }
 EXPORT_SYMBOL_GPL(kho_retrieve_subtree);
 
-/* Handling for debugfs/kho/in */
-
-static __init int kho_in_debugfs_init(const void *fdt)
-{
-	struct dentry *sub_fdt_dir;
-	int err, child;
-
-	kho_in.dir = debugfs_create_dir("in", debugfs_root);
-	if (IS_ERR(kho_in.dir))
-		return PTR_ERR(kho_in.dir);
-
-	sub_fdt_dir = debugfs_create_dir("sub_fdts", kho_in.dir);
-	if (IS_ERR(sub_fdt_dir)) {
-		err = PTR_ERR(sub_fdt_dir);
-		goto err_rmdir;
-	}
-
-	err = kho_debugfs_fdt_add(&kho_in.fdt_list, kho_in.dir, "fdt", fdt);
-	if (err)
-		goto err_rmdir;
-
-	fdt_for_each_subnode(child, fdt, 0) {
-		int len = 0;
-		const char *name = fdt_get_name(fdt, child, NULL);
-		const u64 *fdt_phys;
-
-		fdt_phys = fdt_getprop(fdt, child, "fdt", &len);
-		if (!fdt_phys)
-			continue;
-		if (len != sizeof(*fdt_phys)) {
-			pr_warn("node `%s`'s prop `fdt` has invalid length: %d\n",
-				name, len);
-			continue;
-		}
-		err = kho_debugfs_fdt_add(&kho_in.fdt_list, sub_fdt_dir, name,
-					  phys_to_virt(*fdt_phys));
-		if (err) {
-			pr_warn("failed to add fdt `%s` to debugfs: %d\n", name,
-				err);
-			continue;
-		}
-	}
-
-	return 0;
-
-err_rmdir:
-	debugfs_remove_recursive(kho_in.dir);
-	return err;
-}
-
 static __init int kho_init(void)
 {
 	int err = 0;
@@ -1403,27 +1243,16 @@ static __init int kho_init(void)
 		goto err_free_scratch;
 	}
 
-	debugfs_root = debugfs_create_dir("kho", NULL);
-	if (IS_ERR(debugfs_root)) {
-		err = -ENOENT;
+	err = kho_debugfs_init();
+	if (err)
 		goto err_free_fdt;
-	}
 
-	err = kho_out_debugfs_init();
+	err = kho_out_debugfs_init(&kho_out.dbg);
 	if (err)
 		goto err_free_fdt;
 
 	if (fdt) {
-		err = kho_in_debugfs_init(fdt);
-		/*
-		 * Failure to create /sys/kernel/debug/kho/in does not prevent
-		 * reviving state from KHO and setting up KHO for the next
-		 * kexec.
-		 */
-		if (err)
-			pr_err("failed exposing handover FDT in debugfs: %d\n",
-			       err);
-
+		kho_in_debugfs_init(&kho_in.dbg, fdt);
 		return 0;
 	}
 
diff --git a/kernel/kexec_handover_debugfs.c a/kernel/kexec_handover_debugfs.c
new file mode 100644
--- /dev/null
+++ a/kernel/kexec_handover_debugfs.c
@@ -0,0 +1,216 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * kexec_handover_debugfs.c - kexec handover debugfs interfaces
+ * Copyright (C) 2023 Alexander Graf <graf@amazon.com>
+ * Copyright (C) 2025 Microsoft Corporation, Mike Rapoport <rppt@kernel.org>
+ * Copyright (C) 2025 Google LLC, Changyuan Lyu <changyuanl@google.com>
+ * Copyright (C) 2025 Google LLC, Pasha Tatashin <pasha.tatashin@soleen.com>
+ */
+
+#define pr_fmt(fmt) "KHO: " fmt
+
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/libfdt.h>
+#include <linux/mm.h>
+#include "kexec_handover_internal.h"
+
+static struct dentry *debugfs_root;
+
+struct fdt_debugfs {
+	struct list_head list;
+	struct debugfs_blob_wrapper wrapper;
+	struct dentry *file;
+};
+
+static int __kho_debugfs_fdt_add(struct list_head *list, struct dentry *dir,
+				 const char *name, const void *fdt)
+{
+	struct fdt_debugfs *f;
+	struct dentry *file;
+
+	f = kmalloc(sizeof(*f), GFP_KERNEL);
+	if (!f)
+		return -ENOMEM;
+
+	f->wrapper.data = (void *)fdt;
+	f->wrapper.size = fdt_totalsize(fdt);
+
+	file = debugfs_create_blob(name, 0400, dir, &f->wrapper);
+	if (IS_ERR(file)) {
+		kfree(f);
+		return PTR_ERR(file);
+	}
+
+	f->file = file;
+	list_add(&f->list, list);
+
+	return 0;
+}
+
+int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name,
+			const void *fdt, bool root)
+{
+	struct dentry *dir;
+
+	if (root)
+		dir = dbg->dir;
+	else
+		dir = dbg->sub_fdt_dir;
+
+	return __kho_debugfs_fdt_add(&dbg->fdt_list, dir, name, fdt);
+}
+
+void kho_debugfs_cleanup(struct kho_debugfs *dbg)
+{
+	struct fdt_debugfs *ff, *tmp;
+
+	list_for_each_entry_safe(ff, tmp, &dbg->fdt_list, list) {
+		debugfs_remove(ff->file);
+		list_del(&ff->list);
+		kfree(ff);
+	}
+}
+
+static int kho_out_finalize_get(void *data, u64 *val)
+{
+	*val = kho_finalized();
+
+	return 0;
+}
+
+static int kho_out_finalize_set(void *data, u64 val)
+{
+	if (val)
+		return kho_finalize();
+	else
+		return kho_abort();
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(kho_out_finalize_fops, kho_out_finalize_get,
+			 kho_out_finalize_set, "%llu\n");
+
+static int scratch_phys_show(struct seq_file *m, void *v)
+{
+	for (int i = 0; i < kho_scratch_cnt; i++)
+		seq_printf(m, "0x%llx\n", kho_scratch[i].addr);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(scratch_phys);
+
+static int scratch_len_show(struct seq_file *m, void *v)
+{
+	for (int i = 0; i < kho_scratch_cnt; i++)
+		seq_printf(m, "0x%llx\n", kho_scratch[i].size);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(scratch_len);
+
+__init void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt)
+{
+	struct dentry *dir, *sub_fdt_dir;
+	int err, child;
+
+	INIT_LIST_HEAD(&dbg->fdt_list);
+
+	dir = debugfs_create_dir("in", debugfs_root);
+	if (IS_ERR(dir)) {
+		err = PTR_ERR(dir);
+		goto err_out;
+	}
+
+	sub_fdt_dir = debugfs_create_dir("sub_fdts", dir);
+	if (IS_ERR(sub_fdt_dir)) {
+		err = PTR_ERR(sub_fdt_dir);
+		goto err_rmdir;
+	}
+
+	err = __kho_debugfs_fdt_add(&dbg->fdt_list, dir, "fdt", fdt);
+	if (err)
+		goto err_rmdir;
+
+	fdt_for_each_subnode(child, fdt, 0) {
+		int len = 0;
+		const char *name = fdt_get_name(fdt, child, NULL);
+		const u64 *fdt_phys;
+
+		fdt_phys = fdt_getprop(fdt, child, "fdt", &len);
+		if (!fdt_phys)
+			continue;
+		if (len != sizeof(*fdt_phys)) {
+			pr_warn("node %s prop fdt has invalid length: %d\n",
+				name, len);
+			continue;
+		}
+		err = __kho_debugfs_fdt_add(&dbg->fdt_list, sub_fdt_dir, name,
+					    phys_to_virt(*fdt_phys));
+		if (err) {
+			pr_warn("failed to add fdt %s to debugfs: %d\n", name,
+				err);
+			continue;
+		}
+	}
+
+	dbg->dir = dir;
+	dbg->sub_fdt_dir = sub_fdt_dir;
+
+	return;
+err_rmdir:
+	debugfs_remove_recursive(dir);
+err_out:
+	/*
+	 * Failure to create /sys/kernel/debug/kho/in does not prevent
+	 * reviving state from KHO and setting up KHO for the next
+	 * kexec.
+	 */
+	if (err)
+		pr_err("failed exposing handover FDT in debugfs: %d\n", err);
+}
+
+__init int kho_out_debugfs_init(struct kho_debugfs *dbg)
+{
+	struct dentry *dir, *f, *sub_fdt_dir;
+
+	INIT_LIST_HEAD(&dbg->fdt_list);
+
+	dir = debugfs_create_dir("out", debugfs_root);
+	if (IS_ERR(dir))
+		return -ENOMEM;
+
+	sub_fdt_dir = debugfs_create_dir("sub_fdts", dir);
+	if (IS_ERR(sub_fdt_dir))
+		goto err_rmdir;
+
+	f = debugfs_create_file("scratch_phys", 0400, dir, NULL,
+				&scratch_phys_fops);
+	if (IS_ERR(f))
+		goto err_rmdir;
+
+	f = debugfs_create_file("scratch_len", 0400, dir, NULL,
+				&scratch_len_fops);
+	if (IS_ERR(f))
+		goto err_rmdir;
+
+	f = debugfs_create_file("finalize", 0600, dir, NULL,
+				&kho_out_finalize_fops);
+	if (IS_ERR(f))
+		goto err_rmdir;
+
+	dbg->dir = dir;
+	dbg->sub_fdt_dir = sub_fdt_dir;
+	return 0;
+
+err_rmdir:
+	debugfs_remove_recursive(dir);
+	return -ENOENT;
+}
+
+__init int kho_debugfs_init(void)
+{
+	debugfs_root = debugfs_create_dir("kho", NULL);
+	if (IS_ERR(debugfs_root))
+		return -ENOENT;
+	return 0;
+}
--- a/kernel/kexec_handover_internal.h~kho-make-debugfs-interface-optional
+++ a/kernel/kexec_handover_internal.h
@@ -2,8 +2,47 @@
 #ifndef LINUX_KEXEC_HANDOVER_INTERNAL_H
 #define LINUX_KEXEC_HANDOVER_INTERNAL_H
 
+#include <linux/kexec_handover.h>
+#include <linux/list.h>
 #include <linux/types.h>
 
+#ifdef CONFIG_KEXEC_HANDOVER_DEBUGFS
+#include <linux/debugfs.h>
+
+struct kho_debugfs {
+	struct dentry *dir;
+	struct dentry *sub_fdt_dir;
+	struct list_head fdt_list;
+};
+
+#else
+struct kho_debugfs {};
+#endif
+
+extern struct kho_scratch *kho_scratch;
+extern unsigned int kho_scratch_cnt;
+
+bool kho_finalized(void);
+int kho_finalize(void);
+int kho_abort(void);
+
+#ifdef CONFIG_KEXEC_HANDOVER_DEBUGFS
+int kho_debugfs_init(void);
+void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt);
+int kho_out_debugfs_init(struct kho_debugfs *dbg);
+int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name,
+			const void *fdt, bool root);
+void kho_debugfs_cleanup(struct kho_debugfs *dbg);
+#else
+static inline int kho_debugfs_init(void) { return 0; }
+static inline void kho_in_debugfs_init(struct kho_debugfs *dbg,
+				       const void *fdt) { }
+static inline int kho_out_debugfs_init(struct kho_debugfs *dbg) { return 0; }
+static inline int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name,
+				      const void *fdt, bool root) { return 0; }
+static inline void kho_debugfs_cleanup(struct kho_debugfs *dbg) {}
+#endif /* CONFIG_KEXEC_HANDOVER_DEBUGFS */
+
 #ifdef CONFIG_KEXEC_HANDOVER_DEBUG
 bool kho_scratch_overlap(phys_addr_t phys, size_t size);
 #else
--- a/kernel/Makefile~kho-make-debugfs-interface-optional
+++ a/kernel/Makefile
@@ -84,6 +84,7 @@ obj-$(CONFIG_KEXEC_FILE) += kexec_file.o
 obj-$(CONFIG_KEXEC_ELF) += kexec_elf.o
 obj-$(CONFIG_KEXEC_HANDOVER) += kexec_handover.o
 obj-$(CONFIG_KEXEC_HANDOVER_DEBUG) += kexec_handover_debug.o
+obj-$(CONFIG_KEXEC_HANDOVER_DEBUGFS) += kexec_handover_debugfs.o
 obj-$(CONFIG_BACKTRACE_SELF_TEST) += backtracetest.o
 obj-$(CONFIG_COMPAT) += compat.o
 obj-$(CONFIG_CGROUPS) += cgroup/
--- a/MAINTAINERS~kho-make-debugfs-interface-optional
+++ a/MAINTAINERS
@@ -13796,7 +13796,7 @@ S:	Maintained
 F:	Documentation/admin-guide/mm/kho.rst
 F:	Documentation/core-api/kho/*
 F:	include/linux/kexec_handover.h
-F:	kernel/kexec_handover.c
+F:	kernel/kexec_handover*
 F:	tools/testing/selftests/kho/
 
 KEYS-ENCRYPTED
--- a/tools/testing/selftests/kho/vmtest.sh~kho-make-debugfs-interface-optional
+++ a/tools/testing/selftests/kho/vmtest.sh
@@ -59,6 +59,7 @@ function build_kernel() {
 	tee "$kconfig" > "$kho_config" <<EOF
 CONFIG_BLK_DEV_INITRD=y
 CONFIG_KEXEC_HANDOVER=y
+CONFIG_KEXEC_HANDOVER_DEBUGFS=y
 CONFIG_TEST_KEXEC_HANDOVER=y
 CONFIG_DEBUG_KERNEL=y
 CONFIG_DEBUG_VM=y
_

Patches currently in -mm which might be from pasha.tatashin@soleen.com are

liveupdate-kho-warn-and-fail-on-metadata-or-preserved-memory-in-scratch-area.patch
liveupdate-kho-increase-metadata-bitmap-size-to-page_size.patch
liveupdate-kho-allocate-metadata-directly-from-the-buddy-allocator.patch
kho-make-debugfs-interface-optional.patch
kho-add-interfaces-to-unpreserve-folios-page-ranges-and-vmalloc.patch
memblock-unpreserve-memory-in-case-of-error.patch
test_kho-unpreserve-memory-in-case-of-error.patch
kho-dont-unpreserve-memory-during-abort.patch
liveupdate-kho-move-to-kernel-liveupdate.patch
maintainers-update-kho-maintainers.patch