[PATCH v8 19/30] mm: free PMD swap entries in zap_huge_pmd()

[Usama Arif <usama.arif@linux.dev>]

zap_huge_pmd() assumes any non-present PMD it clears references a folio, so
a PMD swap entry would reach normal_or_softleaf_folio_pmd() and warn.
Worse, nothing would release the slots it points at: unmapping a
swapped-out THP would leak the whole PMD's worth of swap.

Handle it before the folio lookup, as zap_pte_range() already does for a
PTE swap entry.

Signed-off-by: Usama Arif <usama.arif@linux.dev>
---
 mm/huge_memory.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 56eb87fa98376..9cf7c4747cac9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2605,6 +2605,16 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	arch_check_zapped_pmd(vma, orig_pmd);
 	tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
 
+	if (pmd_is_swap_entry(orig_pmd)) {
+		softleaf_t entry = softleaf_from_pmd(orig_pmd);
+
+		zap_deposited_table(mm, pmd);
+		spin_unlock(ptl);
+		swap_put_entries_direct(entry, HPAGE_PMD_NR);
+		add_mm_counter(mm, MM_SWAPENTS, -HPAGE_PMD_NR);
+		return true;
+	}
+
 	is_present = pmd_present(orig_pmd);
 	folio = normal_or_softleaf_folio_pmd(vma, addr, orig_pmd, is_present);
 	has_deposit = has_deposited_pgtable(vma, orig_pmd, folio);
-- 
2.53.0-Meta