[PATCH v2 2/3] mm/hugetlb: Preserve persistent flags when returning folios to the pool

[Kaitao Cheng <kaitao.cheng@linux.dev>]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

add_hugetlb_folio() returns a folio to the HugeTLB pool when vmemmap
restoration fails. It clears folio->private and restores only
HPG_vmemmap_optimized, losing other flags that must survive the rollback.

Clearing HPG_cma causes a later free to bypass the CMA release path,
leaving the CMA allocation bitmap set. Clearing HPG_raw_hwp_unreliable
loses the indication that the locations of poisoned subpages are unknown,
undermining the checks that prevent freeing or unpoisoning such folios.

Preserve the existing flags instead of resetting folio->private. Callers
already clear HPG_restore_reserve, HPG_migratable and HPG_freed before
returning a folio to the pool. Clear HPG_temporary in free_huge_folio()
before attempting to free a temporary folio, so a failed vmemmap restore
does not leave that flag set on a folio returned as surplus.

Add a VM_WARN_ON_ONCE_FOLIO() check for flags other than
HPG_vmemmap_optimized, HPG_raw_hwp_unreliable and HPG_cma to detect
incomplete transient flag cleanup.

Fixes: 161df60e9e89 ("mm, hwpoison, hugetlb: support saving mechanism of raw error pages")
Fixes: d2d786714080 ("mm/hugetlb: enable bootmem allocation from CMA areas")
Closes: https://sashiko.dev/#/bug/linux-5363eb09-9c3c-4f8b-9f3c-a998a8c4b258
Suggested-by: David Hildenbrand <david@kernel.org>
Suggested-by: Muchun Song <muchun.song@linux.dev>
Suggested-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
 mm/hugetlb.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4a008afaedf9..931ca3a30773 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1443,6 +1443,12 @@ void add_hugetlb_folio(struct hstate *h, struct folio *folio,
 
 	lockdep_assert_held(&hugetlb_lock);
 
+	/* Callers must clear transient flags before returning to the pool. */
+	VM_WARN_ON_ONCE_FOLIO((unsigned long)folio->private &
+			     ~(BIT(HPG_vmemmap_optimized) |
+			       BIT(HPG_raw_hwp_unreliable) |
+			       BIT(HPG_cma)), folio);
+
 	INIT_LIST_HEAD(&folio->lru);
 	h->nr_huge_pages++;
 	h->nr_huge_pages_node[nid]++;
@@ -1453,9 +1459,6 @@ void add_hugetlb_folio(struct hstate *h, struct folio *folio,
 	}
 
 	__folio_set_hugetlb(folio);
-	/* Clear all folio->private flags except hugetlb_vmemmap_optimized. */
-	folio->private = NULL;
-	folio_set_hugetlb_vmemmap_optimized(folio);
 
 	arch_clear_hugetlb_flags(folio);
 	enqueue_hugetlb_folio(h, folio);
@@ -1743,6 +1746,7 @@ void free_huge_folio(struct folio *folio)
 		h->resv_huge_pages++;
 
 	if (folio_test_hugetlb_temporary(folio)) {
+		folio_clear_hugetlb_temporary(folio);
 		remove_hugetlb_folio(h, folio, false);
 		spin_unlock_irqrestore(&hugetlb_lock, flags);
 		update_and_free_hugetlb_folio(h, folio, true);
-- 
2.54.0 (Apple Git-157)