[PATCH 1/4] x86/mm: fix missing pgtable destructor for vmemmap tables

[Muchun Song <songmuchun@bytedance.com>]

Since commit 49f599666420 ("mm: call ctor/dtor for kernel PTEs"),
pte_alloc_one_kernel() runs the page-table constructor for kernel PTE
tables.

HugeTLB vmemmap optimization uses pte_alloc_one_kernel() when splitting
a PMD. Restoring the vmemmap backing pages does not collapse the PTE
table, so a later memory hot-remove eventually frees that table through
free_pagetable(). That path currently calls pagetable_free() directly
without decrementing NR_PAGETABLE.

Use PageTable() to identify constructor-backed tables and run the
matching destructor before freeing them. Keep reserved and
constructor-free tables on their existing paths. This also prepares
vmemmap teardown for generic runtime allocations through the normal
pgalloc helpers.

Fixes: 49f599666420 ("mm: call ctor/dtor for kernel PTEs")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/x86/mm/init_64.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 70e682180291..a3ea627157ab 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1003,6 +1003,8 @@ static void __meminit free_pagetable(struct page *page)
 {
 	if (PageReserved(page))
 		free_reserved_page(page);
+	else if (PageTable(page))
+		pagetable_dtor_free(page_ptdesc(page));
 	else
 		pagetable_free(page_ptdesc(page));
 }
-- 
2.54.0