+ mm-hugetlb-preserve-persistent-flags-when-returning-folios-to-the-pool.patch added to mm-unstable branch

+ mm-hugetlb-preserve-persistent-flags-when-returning-folios-to-the-pool.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/hugetlb: preserve persistent flags when returning folios to the pool
has been added to the -mm mm-unstable branch.  Its filename is
     mm-hugetlb-preserve-persistent-flags-when-returning-folios-to-the-pool.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-preserve-persistent-flags-when-returning-folios-to-the-pool.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Kaitao Cheng <chengkaitao@kylinos.cn>
Subject: mm/hugetlb: preserve persistent flags when returning folios to the pool
Date: Fri, 06 Nov 2026 18:05:19 +0800

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.

Link: https://lore.kernel.org/20261106100521.30099-3-kaitao.cheng@linux.dev
Fixes: 161df60e9e89 ("mm, hwpoison, hugetlb: support saving mechanism of raw error pages")
Fixes: d2d786714080 ("mm/hugetlb: enable bootmem allocation from CMA areas")
Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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>
Acked-by: Muchun Song <muchun.song@linux.dev>
Acked-by: Zi Yan <ziy@nvidia.com>
Acked-by: Qi Zheng <qi.zheng@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Mani Tofigh <mt4022@columbia.edu>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: "Oscar Salvador (SUSE)" <osalvador@kernel.org>
---

 mm/hugetlb.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-preserve-persistent-flags-when-returning-folios-to-the-pool
+++ a/mm/hugetlb.c
@@ -1443,6 +1443,12 @@ void add_hugetlb_folio(struct hstate *h,
 
 	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,
 	}
 
 	__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);
_

Patches currently in -mm which might be from chengkaitao@kylinos.cn are

mm-hugetlb_cma-fix-incorrect-hugetlb_cma_size-assignment-on-malformed-input.patch
mm-hugetlb-preserve-persistent-flags-when-returning-folios-to-the-pool.patch
mm-hugetlb-fix-nr_hugetlb-accounting-for-unused-surplus-folios.patch
mm-hugetlb-account-nr_hugetlb-at-folio-state-transitions.patch