linux-kernel - [PATCH v1 05/13] kho: Always expose output FDT in debugfs

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Message-ID: <20251114155358.2884014-6-pasha.tatashin@soleen.com>
Date: Fri, 14 Nov 2025 10:53:50 -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 v1 05/13] kho: Always expose output FDT in debugfs

Currently, the output FDT is added to debugfs only when KHO is
finalized and removed when aborted.

There is no need to hide the FDT based on the state. Always expose it
starting from initialization. This aids the transition toward removing
the explicit abort functionality and converting KHO to be fully
stateless.

Also, pre-zero the FDT tree so we do not expose random bits to the
user and to the next kernel.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 kernel/liveupdate/kexec_handover.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 83aca3b4af15..cd8641725343 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -1147,8 +1147,6 @@ int kho_abort(void)
 	__kho_abort();
 	kho_out.finalized = false;
 
-	kho_debugfs_fdt_remove(&kho_out.dbg, kho_out.fdt);
-
 	return 0;
 }
 
@@ -1219,9 +1217,6 @@ int kho_finalize(void)
 
 	kho_out.finalized = true;
 
-	WARN_ON_ONCE(kho_debugfs_fdt_add(&kho_out.dbg, "fdt",
-					 kho_out.fdt, true));
-
 	return 0;
 }
 
@@ -1310,7 +1305,7 @@ static __init int kho_init(void)
 	if (!kho_enable)
 		return 0;
 
-	fdt_page = alloc_page(GFP_KERNEL);
+	fdt_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
 	if (!fdt_page) {
 		err = -ENOMEM;
 		goto err_free_scratch;
@@ -1344,6 +1339,9 @@ static __init int kho_init(void)
 			init_cma_reserved_pageblock(pfn_to_page(pfn));
 	}
 
+	WARN_ON_ONCE(kho_debugfs_fdt_add(&kho_out.dbg, "fdt",
+					 kho_out.fdt, true));
+
 	return 0;
 
 err_free_fdt:
-- 
2.52.0.rc1.455.g30608eb744-goog