Subject: [RFC PATCH 04/20] kho: add callback for table pages

From: Jork Loeser <[email-masked]>
Date: Wed, 27 May 2026 17:41:46 -0700

From: "Pratyush Yadav (Google)" <[email-masked]>

The KHO memory preservation radix tree does not mark the table pages
themselves as scratch. This is done to avoid a circular dependency where
preserving a page can lead of allocating other preserved pages. This
means any walker looking for free ranges of memory outside of scratch
areas will ignore the table

Add a table callback that is invoked for each table page. The callback
is given the physical address of the table page.

Signed-off-by: Pratyush Yadav (Google) <[email-masked]>
Signed-off-by: Jork Loeser <[email-masked]>
---
 include/linux/kho_radix_tree.h     |  3 +++
 kernel/liveupdate/kexec_handover.c | 12 ++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/kho_radix_tree.h b/include/linux/kho_radix_tree.h
index 030da6399d28..fe7151d89361 100644
--- a/include/linux/kho_radix_tree.h
+++ b/include/linux/kho_radix_tree.h
@@ -37,12 +37,15 @@ struct kho_radix_tree {
 /**
  * struct kho_radix_walk_cb - Callbacks for KHO radix tree walk.
  * @key:      Called on each present key in the radix tree.
+ * @table:    Called on each table of the radix tree itself. Receives the
+ *            physical address of the page containing the table.
  *
  * For each callback, a return value of 0 continues the walk and a non-zero
  * return value is directly returned to the caller.
  */
 struct kho_radix_walk_cb {
 	int (*key)(unsigned long key);
+	int (*table)(phys_addr_t phys);
 };
 
 #ifdef CONFIG_KEXEC_HANDOVER
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index b22b3cec251e..0f8d058f1a27 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -273,6 +273,12 @@ static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf, unsigned long key,
 	unsigned int i;
 	int err;
 
+	if (cb->table) {
+		err = cb->table(virt_to_phys(leaf));
+		if (err)
+			return err;
+	}
+
 	if (!cb->key)
 		return 0;
 
@@ -295,6 +301,12 @@ static int __kho_radix_walk_tree(struct kho_radix_node *root,
 	unsigned int shift;
 	int err;
 
+	if (cb->table) {
+		err = cb->table(virt_to_phys(root));
+		if (err)
+			return err;
+	}
+
 	for (i = 0; i < PAGE_SIZE / sizeof(phys_addr_t); i++) {
 		if (!root->table[i])
 			continue;
-- 
2.43.0