[PATCH v9 2/3] kho: make preserved pages compatible with deferred struct page init

Michal Clapinski
2026-04-23T12:25:51Z

From: Evangelos Petrongonas <epetron@amazon.de>

When CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, struct page
initialization is deferred to parallel kthreads that run later
in the boot process.

During KHO restoration, kho_preserved_memory_reserve() writes metadata
for each preserved memory region. However, if the struct page has not
been initialized, this write targets uninitialized memory, potentially
leading to errors like:
BUG: unable to handle page fault for address: ...

Fix this by introducing kho_get_preserved_page(), which ensures
all struct pages in a preserved region are initialized by calling
init_deferred_page() which is a no-op when the struct page is already
initialized.

Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
Co-developed-by: Michal Clapinski <mclapinski@google.com>
Signed-off-by: Michal Clapinski <mclapinski@google.com>
Reviewed-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
kernel/liveupdate/Kconfig | 2 --
kernel/liveupdate/kexec_handover.c | 27 ++++++++++++++++++++++++++-
2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig
index 1a8513f16ef7..c13af38ba23a 100644
--- a/kernel/liveupdate/Kconfig
+++ b/kernel/liveupdate/Kconfig
@@ -1,12 +1,10 @@
# SPDX-License-Identifier: GPL-2.0-only

menu "Live Update and Kexec HandOver"
- depends on !DEFERRED_STRUCT_PAGE_INIT

config KEXEC_HANDOVER
bool "kexec handover"
depends on ARCH_SUPPORTS_KEXEC_HANDOVER && ARCH_SUPPORTS_KEXEC_FILE
- depends on !DEFERRED_STRUCT_PAGE_INIT
select MEMBLOCK_KHO_SCRATCH
select KEXEC_FILE
select LIBFDT
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index a507366a2cf9..d5718bef6d4d 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -473,6 +473,31 @@ struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages)
}
EXPORT_SYMBOL_GPL(kho_restore_pages);

+/*
+ * With CONFIG_DEFERRED_STRUCT_PAGE_INIT, struct pages in higher memory regions
+ * may not be initialized yet at the time KHO deserializes preserved memory.
+ * KHO uses the struct page to store metadata and a later initialization would
+ * overwrite it.
+ * Ensure all the struct pages in the preservation are
+ * initialized. kho_preserved_memory_reserve() marks the reservation as noinit
+ * to make sure they don't get re-initialized later.
+ */
+static struct page *__init kho_get_preserved_page(phys_addr_t phys,
+ unsigned int order)
+{
+ unsigned long pfn = PHYS_PFN(phys);
+ int nid;
+
+ if (!IS_ENABLED(CONFIG_DEFERRED_STRUCT_PAGE_INIT))
+ return pfn_to_page(pfn);
+
+ nid = early_pfn_to_nid(pfn);
+ for (unsigned long i = 0; i < (1UL << order); i++)
+ init_deferred_page(pfn + i, nid);
+
+ return pfn_to_page(pfn);
+}
+
static int __init kho_preserved_memory_reserve(phys_addr_t phys,
unsigned int order)
{
@@ -481,7 +506,7 @@ static int __init kho_preserved_memory_reserve(phys_addr_t phys,
u64 sz;

sz = 1 << (order + PAGE_SHIFT);
- page = phys_to_page(phys);
+ page = kho_get_preserved_page(phys, order);

/* Reserve the memory preserved in KHO in memblock */
memblock_reserve(phys, sz);
--
2.54.0.rc2.533.g4f5dca5207-goog