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

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/hugetlb: preserve persistent flags when returning folios to the pool
has been added to the -mm mm-new 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-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Kaitao Cheng <chengkaitao@kylinos.cn>
Subject: mm/hugetlb: preserve persistent flags when returning folios to the pool
Date: Mon, 02 Nov 2026 10:49:09 +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/20261102024910.31486-3-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: Qi Zheng <qi.zheng@linux.dev>
Acked-by: Zi Yan <ziy@nvidia.com>
Acked-by: Muchun Song <muchun.song@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>
---

 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-surplus-folios.patch