[PATCH v2 1/2] kho: move sanity checks to kho_restore_page()

[Pratyush Yadav]

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.

Signed-off-by: Pratyush Yadav <pratyush at kernel.org>
---

Notes:
    Changes in v2:
    
    - New in v2.

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

diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
index ecd1ac210dbd7..69cab82abaaef 100644
--- a/kernel/kexec_handover.c
+++ b/kernel/kexec_handover.c
@@ -183,10 +183,18 @@ static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn,
 	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);
@@ -199,6 +207,7 @@ static void kho_restore_page(struct page *page, unsigned int order)
 		prep_compound_page(page, order);
 
 	adjust_managed_page_count(page, nr_pages);
+	return page;
 }
 
 /**
@@ -209,18 +218,9 @@ static void kho_restore_page(struct page *page, unsigned int order)
  */
 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);
 
-- 
2.47.3