[merged mm-stable] kho-remove-finalize-state-and-clients.patch removed from -mm tree

[merged mm-stable] kho-remove-finalize-state-and-clients.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: kho: remove finalize state and clients
has been removed from the -mm tree.  Its filename was
     kho-remove-finalize-state-and-clients.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Jason Miu <jasonmiu@google.com>
Subject: kho: remove finalize state and clients
Date: Thu, 5 Feb 2026 18:14:28 -0800

Eliminate the `kho_finalize()` function and its associated state from the
KHO subsystem.  The transition to a radix tree for memory tracking makes
the explicit "finalize" state and its serialization step obsolete.

Remove the `kho_finalize()` and `kho_finalized()` APIs and their stub
implementations.  Update KHO client code and the debugfs interface to no
longer call or depend on the `kho_finalize()` mechanism.

Complete the move towards a stateless KHO, simplifying the overall design
by removing unnecessary state management.

Link: https://lkml.kernel.org/r/20260206021428.3386442-3-jasonmiu@google.com
Signed-off-by: Jason Miu <jasonmiu@google.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: David Matlack <dmatlack@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 Documentation/admin-guide/mm/kho.rst        |   53 +++---------------
 Documentation/core-api/kho/index.rst        |   12 ----
 kernel/liveupdate/kexec_handover.c          |   21 -------
 kernel/liveupdate/kexec_handover_debugfs.c  |   23 -------
 kernel/liveupdate/kexec_handover_internal.h |    3 -
 kernel/liveupdate/luo_core.c                |   12 ----
 tools/testing/selftests/kho/init.c          |   20 ------
 7 files changed, 13 insertions(+), 131 deletions(-)

--- a/Documentation/admin-guide/mm/kho.rst~kho-remove-finalize-state-and-clients
+++ a/Documentation/admin-guide/mm/kho.rst
@@ -28,20 +28,10 @@ per NUMA node scratch regions on boot.
 Perform a KHO kexec
 ===================
 
-First, before you perform a KHO kexec, you need to move the system into
-the :ref:`KHO finalization phase <kho-finalization-phase>` ::
-
-  $ echo 1 > /sys/kernel/debug/kho/out/finalize
-
-After this command, the KHO FDT is available in
-``/sys/kernel/debug/kho/out/fdt``. Other subsystems may also register
-their own preserved sub FDTs under
-``/sys/kernel/debug/kho/out/sub_fdts/``.
-
-Next, load the target payload and kexec into it. It is important that you
-use the ``-s`` parameter to use the in-kernel kexec file loader, as user
-space kexec tooling currently has no support for KHO with the user space
-based file loader ::
+To perform a KHO kexec, load the target payload and kexec into it. It
+is important that you use the ``-s`` parameter to use the in-kernel
+kexec file loader, as user space kexec tooling currently has no
+support for KHO with the user space based file loader ::
 
   # kexec -l /path/to/bzImage --initrd /path/to/initrd -s
   # kexec -e
@@ -52,40 +42,19 @@ For example, if you used ``reserve_mem``
 an early memory reservation, the new kernel will have that memory at the
 same physical address as the old kernel.
 
-Abort a KHO exec
-================
-
-You can move the system out of KHO finalization phase again by calling ::
-
-  $ echo 0 > /sys/kernel/debug/kho/out/active
-
-After this command, the KHO FDT is no longer available in
-``/sys/kernel/debug/kho/out/fdt``.
-
 debugfs Interfaces
 ==================
 
+These debugfs interfaces are available when the kernel is compiled with
+``CONFIG_KEXEC_HANDOVER_DEBUGFS`` enabled.
+
 Currently KHO creates the following debugfs interfaces. Notice that these
 interfaces may change in the future. They will be moved to sysfs once KHO is
 stabilized.
 
-``/sys/kernel/debug/kho/out/finalize``
-    Kexec HandOver (KHO) allows Linux to transition the state of
-    compatible drivers into the next kexec'ed kernel. To do so,
-    device drivers will instruct KHO to preserve memory regions,
-    which could contain serialized kernel state.
-    While the state is serialized, they are unable to perform
-    any modifications to state that was serialized, such as
-    handed over memory allocations.
-
-    When this file contains "1", the system is in the transition
-    state. When contains "0", it is not. To switch between the
-    two states, echo the respective number into this file.
-
 ``/sys/kernel/debug/kho/out/fdt``
-    When KHO state tree is finalized, the kernel exposes the
-    flattened device tree blob that carries its current KHO
-    state in this file. Kexec user space tooling can use this
+    The kernel exposes the flattened device tree blob that carries its
+    current KHO state in this file. Kexec user space tooling can use this
     as input file for the KHO payload image.
 
 ``/sys/kernel/debug/kho/out/scratch_len``
@@ -100,8 +69,8 @@ stabilized.
     it should place its payload images.
 
 ``/sys/kernel/debug/kho/out/sub_fdts/``
-    In the KHO finalization phase, KHO producers register their own
-    FDT blob under this directory.
+    KHO producers can register their own FDT or another binary blob under
+    this directory.
 
 ``/sys/kernel/debug/kho/in/fdt``
     When the kernel was booted with Kexec HandOver (KHO),
--- a/Documentation/core-api/kho/index.rst~kho-remove-finalize-state-and-clients
+++ a/Documentation/core-api/kho/index.rst
@@ -71,18 +71,6 @@ for boot memory allocations and as targe
 of that memory region may be reserved. These reservations are irrelevant for
 the next KHO, because kexec can overwrite even the original kernel.
 
-.. _kho-finalization-phase:
-
-KHO finalization phase
-======================
-
-To enable user space based kexec file loader, the kernel needs to be able to
-provide the FDT that describes the current kernel's state before
-performing the actual kexec. The process of generating that FDT is
-called serialization. When the FDT is generated, some properties
-of the system may become immutable because they are already written down
-in the FDT. That state is called the KHO finalization phase.
-
 Kexec Handover Radix Tree
 =========================
 
--- a/kernel/liveupdate/kexec_handover.c~kho-remove-finalize-state-and-clients
+++ a/kernel/liveupdate/kexec_handover.c
@@ -68,8 +68,7 @@ early_param("kho", kho_parse_enable);
 
 struct kho_out {
 	void *fdt;
-	bool finalized;
-	struct mutex lock; /* protects KHO FDT finalization */
+	struct mutex lock; /* protects KHO FDT */
 
 	struct kho_radix_tree radix_tree;
 	struct kho_debugfs dbg;
@@ -80,7 +79,6 @@ static struct kho_out kho_out = {
 	.radix_tree = {
 		.lock = __MUTEX_INITIALIZER(kho_out.radix_tree.lock),
 	},
-	.finalized = false,
 };
 
 /**
@@ -1241,23 +1239,6 @@ void kho_restore_free(void *mem)
 }
 EXPORT_SYMBOL_GPL(kho_restore_free);
 
-int kho_finalize(void)
-{
-	if (!kho_enable)
-		return -EOPNOTSUPP;
-
-	guard(mutex)(&kho_out.lock);
-	kho_out.finalized = true;
-
-	return 0;
-}
-
-bool kho_finalized(void)
-{
-	guard(mutex)(&kho_out.lock);
-	return kho_out.finalized;
-}
-
 struct kho_in {
 	phys_addr_t fdt_phys;
 	phys_addr_t scratch_phys;
--- a/kernel/liveupdate/kexec_handover_debugfs.c~kho-remove-finalize-state-and-clients
+++ a/kernel/liveupdate/kexec_handover_debugfs.c
@@ -76,24 +76,6 @@ void kho_debugfs_fdt_remove(struct kho_d
 	}
 }
 
-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 -EINVAL;
-}
-
-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++)
@@ -199,11 +181,6 @@ __init int kho_out_debugfs_init(struct k
 	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;
--- a/kernel/liveupdate/kexec_handover_internal.h~kho-remove-finalize-state-and-clients
+++ a/kernel/liveupdate/kexec_handover_internal.h
@@ -22,9 +22,6 @@ struct kho_debugfs {};
 extern struct kho_scratch *kho_scratch;
 extern unsigned int kho_scratch_cnt;
 
-bool kho_finalized(void);
-int kho_finalize(void);
-
 #ifdef CONFIG_KEXEC_HANDOVER_DEBUGFS
 int kho_debugfs_init(void);
 void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt);
--- a/kernel/liveupdate/luo_core.c~kho-remove-finalize-state-and-clients
+++ a/kernel/liveupdate/luo_core.c
@@ -230,17 +230,7 @@ int liveupdate_reboot(void)
 
 	luo_flb_serialize();
 
-	err = kho_finalize();
-	if (err) {
-		pr_err("kho_finalize failed %d\n", err);
-		/*
-		 * kho_finalize() may return libfdt errors, to aboid passing to
-		 * userspace unknown errors, change this to EAGAIN.
-		 */
-		err = -EAGAIN;
-	}
-
-	return err;
+	return 0;
 }
 
 /**
--- a/tools/testing/selftests/kho/init.c~kho-remove-finalize-state-and-clients
+++ a/tools/testing/selftests/kho/init.c
@@ -11,7 +11,6 @@
 /* from arch/x86/include/asm/setup.h */
 #define COMMAND_LINE_SIZE	2048
 
-#define KHO_FINALIZE "/debugfs/kho/out/finalize"
 #define KERNEL_IMAGE "/kernel"
 
 static int mount_filesystems(void)
@@ -22,22 +21,6 @@ static int mount_filesystems(void)
 	return mount("proc", "/proc", "proc", 0, NULL);
 }
 
-static int kho_enable(void)
-{
-	const char enable[] = "1";
-	int fd;
-
-	fd = open(KHO_FINALIZE, O_RDWR);
-	if (fd < 0)
-		return -1;
-
-	if (write(fd, enable, sizeof(enable)) != sizeof(enable))
-		return 1;
-
-	close(fd);
-	return 0;
-}
-
 static long kexec_file_load(int kernel_fd, int initrd_fd,
 			    unsigned long cmdline_len, const char *cmdline,
 			    unsigned long flags)
@@ -78,9 +61,6 @@ int main(int argc, char *argv[])
 	if (mount_filesystems())
 		goto err_reboot;
 
-	if (kho_enable())
-		goto err_reboot;
-
 	if (kexec_load())
 		goto err_reboot;
 
_

Patches currently in -mm which might be from jasonmiu@google.com are