[PATCH v3 4/4] arm64/mm: fix destructor for unconstructed hotplug page tables

[Muchun Song]

Commit c594b83457cc ("arm64: mm: call pagetable dtor when freeing
hot-removed page tables") made free_hotplug_pgtable_page()
unconditionally run the page-table destructor. This matches page tables
allocated by the arm64 mapping code, which runs the corresponding
constructors.

However, arm64 also uses the generic sparse-vmemmap population code.
Runtime intermediate page tables allocated by that code do not run a
page-table constructor. Freeing one during memory hot-remove therefore
runs a destructor without a matching constructor and corrupts
NR_PAGETABLE accounting.

Free intermediate page-table pages through pagetable_free(). It runs the
destructor only for constructor-backed pages and then releases the page
through the page-table freeing path.

Fixes: c594b83457cc ("arm64: mm: call pagetable dtor when freeing hot-removed page tables")
Cc: stable at vger.kernel.org
Assisted-by: LLM
Signed-off-by: Muchun Song <songmuchun at bytedance.com>
Reviewed-by: Kevin Brodsky <kevin.brodsky at arm.com>
Acked-by: David Hildenbrand (Arm) <david at kernel.org>
---
v3:
- Collect Acked-by from David Hildenbrand
- Collect Reviewed-by from Kevin Brodsky

v2:
- Free intermediate tables through pagetable_free() (suggested by David
  Hildenbrand)
- Update the commit message for the page-table freeing path
---
 arch/arm64/mm/mmu.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 79d90226fd5d..4dce8fa227c3 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1495,8 +1495,7 @@ static void free_hotplug_page_range(struct page *page, size_t size,
 
 static void free_hotplug_pgtable_page(struct page *page)
 {
-	pagetable_dtor(page_ptdesc(page));
-	free_hotplug_page_range(page, PAGE_SIZE, NULL);
+	pagetable_free(page_ptdesc(page));
 }
 
 static bool pgtable_range_aligned(unsigned long start, unsigned long end,
-- 
2.54.0