+ kho-make-preserved-pages-compatible-with-deferred-struct-page-init.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: kho: make preserved pages compatible with deferred struct page init
has been added to the -mm mm-new branch.  Its filename is
     kho-make-preserved-pages-compatible-with-deferred-struct-page-init.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kho-make-preserved-pages-compatible-with-deferred-struct-page-init.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Evangelos Petrongonas <epetron@amazon.de>
Subject: kho: make preserved pages compatible with deferred struct page init
Date: Tue, 17 Mar 2026 15:15:34 +0100

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.

Link: https://lkml.kernel.org/r/20260317141534.815634-4-mclapinski@google.com
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>
Cc: Alexander Graf <graf@amazon.com>
Cc: Samiullah Khawaja <skhawaja@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/liveupdate/Kconfig          |    2 --
 kernel/liveupdate/kexec_handover.c |   27 ++++++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 3 deletions(-)

--- a/kernel/liveupdate/Kconfig~kho-make-preserved-pages-compatible-with-deferred-struct-page-init
+++ a/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
--- a/kernel/liveupdate/kexec_handover.c~kho-make-preserved-pages-compatible-with-deferred-struct-page-init
+++ a/kernel/liveupdate/kexec_handover.c
@@ -471,6 +471,31 @@ struct page *kho_restore_pages(phys_addr
 }
 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)
 {
@@ -479,7 +504,7 @@ static int __init kho_preserved_memory_r
 	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);
_

Patches currently in -mm which might be from epetron@amazon.de are

kho-make-preserved-pages-compatible-with-deferred-struct-page-init.patch