+ kho-move-sanity-checks-to-kho_restore_page.patch added to mm-new branch

+ kho-move-sanity-checks-to-kho_restore_page.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: kho: move sanity checks to kho_restore_page()
has been added to the -mm mm-new branch.  Its filename is
     kho-move-sanity-checks-to-kho_restore_page.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kho-move-sanity-checks-to-kho_restore_page.patch

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

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patches, and acceptance into mm-new is a notification for others take
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------------------------------------------------------
From: Pratyush Yadav <pratyush@kernel.org>
Subject: kho: move sanity checks to kho_restore_page()
Date: Wed, 17 Sep 2025 14:56:53 +0200

While KHO exposes folio as the primitive externally, internally its
restoration machinery operates on pages.  This can be seen with
kho_restore_folio() for example.  It performs some sanity checks and hands
it over to kho_restore_page() to do the heavy lifting of page restoration.
After the work done by kho_restore_page(), kho_restore_folio() only
converts the head page to folio and returns it.  Similarly,
deserialize_bitmap() operates on the head page directly to store the
order.

Move the sanity checks for valid phys and order from the public-facing
kho_restore_folio() to the private-facing kho_restore_page().  This makes
the boundary between page and folio clearer from KHO's perspective.

While at it, drop the comment above kho_restore_page().  The comment is
misleading now.  The function stopped looking like free_reserved_page()
since 12b9a2c05d1b4 ("kho: initialize tail pages for higher order folios
properly"), and now looks even more different.

Link: https://lkml.kernel.org/r/20250917125725.665-1-pratyush@kernel.org
Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/kexec_handover.c |   28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

--- a/kernel/kexec_handover.c~kho-move-sanity-checks-to-kho_restore_page
+++ a/kernel/kexec_handover.c
@@ -210,10 +210,18 @@ static int __kho_preserve_order(struct k
 	return 0;
 }
 
-/* almost as free_reserved_page(), just don't free the page */
-static void kho_restore_page(struct page *page, unsigned int order)
+static struct page *kho_restore_page(phys_addr_t phys)
 {
-	unsigned int nr_pages = (1 << order);
+	struct page *page = pfn_to_online_page(PHYS_PFN(phys));
+	unsigned int nr_pages, order;
+
+	if (!page)
+		return NULL;
+
+	order = page->private;
+	if (order > MAX_PAGE_ORDER)
+		return NULL;
+	nr_pages = (1 << order);
 
 	/* Head page gets refcount of 1. */
 	set_page_count(page, 1);
@@ -226,6 +234,7 @@ static void kho_restore_page(struct page
 		prep_compound_page(page, order);
 
 	adjust_managed_page_count(page, nr_pages);
+	return page;
 }
 
 /**
@@ -236,18 +245,9 @@ static void kho_restore_page(struct page
  */
 struct folio *kho_restore_folio(phys_addr_t phys)
 {
-	struct page *page = pfn_to_online_page(PHYS_PFN(phys));
-	unsigned long order;
-
-	if (!page)
-		return NULL;
-
-	order = page->private;
-	if (order > MAX_PAGE_ORDER)
-		return NULL;
+	struct page *page = kho_restore_page(phys);
 
-	kho_restore_page(page, order);
-	return page_folio(page);
+	return page ? page_folio(page) : NULL;
 }
 EXPORT_SYMBOL_GPL(kho_restore_folio);
 
_

Patches currently in -mm which might be from pratyush@kernel.org are

kho-move-sanity-checks-to-kho_restore_page.patch
kho-make-sure-page-being-restored-is-actually-from-kho.patch