linux-kernel - [PATCH v2 04/13] kho: Preserve FDT folio only once during initialization

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Message-ID: <20251114190002.3311679-5-pasha.tatashin@soleen.com>
Date: Fri, 14 Nov 2025 13:59:53 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: akpm@...ux-foundation.org,
	bhe@...hat.com,
	pasha.tatashin@...een.com,
	rppt@...nel.org,
	jasonmiu@...gle.com,
	arnd@...db.de,
	coxu@...hat.com,
	dave@...ilevsky.ca,
	ebiggers@...gle.com,
	graf@...zon.com,
	kees@...nel.org,
	linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org,
	linux-mm@...ck.org
Subject: [PATCH v2 04/13] kho: Preserve FDT folio only once during initialization

Currently, the FDT folio is preserved inside __kho_finalize(). If the
user performs multiple finalize/abort cycles, kho_preserve_folio() is
called repeatedly for the same FDT folio.

Since the FDT folio is allocated once during kho_init(), it should be
marked for preservation at the same time. Move the preservation call to
kho_init() to align the preservation state with the object's lifecycle
and simplify the finalize path.

Also, pre-zero the FDT tree so we do not expose random bits to the
user and to the next kernel by using the new kho_alloc_preserve() api.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
Reviewed-by: Pratyush Yadav <pratyush@...nel.org>
---
 kernel/liveupdate/kexec_handover.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 5c5c9c46fe92..704e91418214 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -1251,10 +1251,6 @@ static int __kho_finalize(void)
 	if (err)
 		goto abort;
 
-	err = kho_preserve_folio(virt_to_folio(kho_out.fdt));
-	if (err)
-		goto abort;
-
 	err = kho_mem_serialize(&kho_out);
 	if (err)
 		goto abort;
@@ -1384,19 +1380,17 @@ EXPORT_SYMBOL_GPL(kho_retrieve_subtree);
 
 static __init int kho_init(void)
 {
-	int err = 0;
 	const void *fdt = kho_get_fdt();
-	struct page *fdt_page;
+	int err = 0;
 
 	if (!kho_enable)
 		return 0;
 
-	fdt_page = alloc_page(GFP_KERNEL);
-	if (!fdt_page) {
-		err = -ENOMEM;
+	kho_out.fdt = kho_alloc_preserve(PAGE_SIZE);
+	if (IS_ERR(kho_out.fdt)) {
+		err = PTR_ERR(kho_out.fdt);
 		goto err_free_scratch;
 	}
-	kho_out.fdt = page_to_virt(fdt_page);
 
 	err = kho_debugfs_init();
 	if (err)
@@ -1424,9 +1418,9 @@ static __init int kho_init(void)
 	return 0;
 
 err_free_fdt:
-	put_page(fdt_page);
-	kho_out.fdt = NULL;
+	kho_unpreserve_free(kho_out.fdt);
 err_free_scratch:
+	kho_out.fdt = NULL;
 	for (int i = 0; i < kho_scratch_cnt; i++) {
 		void *start = __va(kho_scratch[i].addr);
 		void *end = start + kho_scratch[i].size;
-- 
2.52.0.rc1.455.g30608eb744-goog