mm/hugetlb: restore reservation on error in hugetlb_mfill_atomic_pte() resubmission path

PATCH In review David Carlier 2 participants 4 messages May 19 – May 20

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Stable branch Memory management HugeTLB

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David Carlier

author

2026-05-19 23:05 UTC #0 lore raw

PATCH v2 1/1 mm/hugetlb: restore reservation on error in hugetlb_mfill_atomic_pte() resubmission path

When the resubmission path in hugetlb_mfill_atomic_pte() allocates a new hugetlb folio via alloc_hugetlb_folio(), a VMA reservation is consumed. If copy_user_large_folio() subsequently fails (e.g. -EHWPOISON when the source page is hwpoisoned), folio_put() restores the global hugetlb pool count through free_huge_folio(), but the per-VMA reservation map entry is left marked consumed.

User-visible effect: on a UFFDIO_COPY into a private hugetlb VMA where the resubmission path's copy fails, the reservation for that address is leaked from the VMA's reserve map. A subsequent fault at the same address takes the no-reservation path, and under hugetlb pool pressure the task is SIGBUSed at an address it had previously reserved. One map entry is leaked per occurrence.

Add the missing restore_reserve_on_error() call before folio_put(), matching the first-attempt error path which already handles this correctly.

Fixes 1cb9dc4b475c ("mm: hwpoison: support recovery from HugePage copy-on-write faults")

Cc <[email protected]>

Signed-off-by David Carlier <[email protected]>

---
v2:
- Add user-visible effects paragraph in changelog (per akpm, required for Cc: stable).
- Correct Fixes: tag to 1cb9dc4b475c (per Muchun) -- the failing arm only exists since copy_user_large_folio() became int-returning.

Andrew, please drop the v1 currently queued as 270157aef0d1 in mm-unstable.

v1: https://lore.kernel.org/all/[email protected]/

 mm/hugetlb.c | 1 +
 1 file changed, 1 insertion(+)

mm/hugetlb.c +1 -0

index 4b80b167cc9c..c6dee98840db 100644
@@ -6270,6 +6270,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
 		folio_put(*foliop);
 		*foliop = NULL;
 		if (ret) {
+			restore_reserve_on_error(h, dst_vma, dst_addr, folio);
 			folio_put(folio);
 			goto out;
 		}

Signature · 1 line

2.53.0

Muchun Song

maintainer

2026-05-20 02:48 UTC #1 lore raw

Quoted 45 lines · David Carlier

When the resubmission path in hugetlb_mfill_atomic_pte() allocates a new hugetlb folio via alloc_hugetlb_folio(), a VMA reservation is consumed. If copy_user_large_folio() subsequently fails (e.g. -EHWPOISON when the source page is hwpoisoned), folio_put() restores the global hugetlb pool count through free_huge_folio(), but the per-VMA reservation map entry is left marked consumed.
User-visible effect: on a UFFDIO_COPY into a private hugetlb VMA where the resubmission path's copy fails, the reservation for that address is leaked from the VMA's reserve map. A subsequent fault at the same address takes the no-reservation path, and under hugetlb pool pressure the task is SIGBUSed at an address it had previously reserved. One map entry is leaked per occurrence.
Add the missing restore_reserve_on_error() call before folio_put(), matching the first-attempt error path which already handles this correctly.
Fixes 1cb9dc4b475c ("mm: hwpoison: support recovery from HugePage copy-on-write faults")
Cc <[email protected]>
Signed-off-by David Carlier <[email protected]>
---
v2:
- Add user-visible effects paragraph in changelog (per akpm, required for Cc: stable).
- Correct Fixes: tag to 1cb9dc4b475c (per Muchun) -- the failing arm only exists since copy_user_large_folio() became int-returning.
Andrew, please drop the v1 currently queued as 270157aef0d1 in mm-unstable.
v1: https://lore.kernel.org/all/[email protected]/
mm/hugetlb.c | 1 +
1 file changed, 1 insertion(+)
mm/hugetlb.c +0 -0
index 4b80b167cc9c..c6dee98840db 100644

mm/hugetlb.c int hugetlb_mfill_atomic_pte(pte_t *dst_pte, · line 6273

Quoted 4 lines

mm/hugetlb.c +1 -0

@@ -6270,6 +6270,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
 	folio_put(*foliop);
 *	foliop = NULL;
 	if (ret) {
+ 		restore_reserve_on_error(h, dst_vma, dst_addr, folio);

I think you should fix the same problem in copy_hugetlb_page_range() within this patch as well since both are introduced by the same commit.

Muchun,
Thanks.

Quoted 6 lines

mm/hugetlb.c +0 -0
 		folio_put(folio);
 		goto out;
 	}
Signature · 1 line
2.53.0

David Carlier

author

2026-05-20 04:49 UTC #2 lore raw

PATCH v3 1/1 mm/hugetlb: restore reservation on error in hugetlb folio copy paths

In reply to David Carlier

Two sites in mm/hugetlb.c allocate a hugetlb folio via alloc_hugetlb_folio() (consuming a VMA reservation) and then call copy_user_large_folio(), which became int-returning in commit 1cb9dc4b475c ("mm: hwpoison: support recovery from HugePage copy-on-write faults") and can now fail (e.g. -EHWPOISON on a hwpoisoned source page). On the failure path, folio_put() restores the global hugetlb pool count through free_huge_folio(), but the per-VMA reservation map entry is left marked consumed:

- hugetlb_mfill_atomic_pte() resubmission path (UFFDIO_COPY)
- copy_hugetlb_page_range() fork-time CoW path when hugetlb_try_dup_anon_rmap() fails (rare: pinned hugetlb anon folio under fork)

User-visible effect: on UFFDIO_COPY into a private hugetlb VMA where the resubmission copy fails, the reservation for that address is leaked from the VMA's reserve map. A subsequent fault at the same address takes the no-reservation path, and under hugetlb pool pressure the task is SIGBUSed at an address it had previously reserved. The fork-time CoW path leaks the same way in the child VMA's reserve map, though it requires the much rarer combination of pinned hugetlb anon page + hwpoisoned source.

Add the missing restore_reserve_on_error() call before folio_put() on both error paths.

Fixes 1cb9dc4b475c ("mm: hwpoison: support recovery from HugePage copy-on-write faults")

Cc <[email protected]>

Signed-off-by David Carlier <[email protected]>

---
v3:
- Fold the copy_hugetlb_page_range() sibling fix into this patch (per Muchun) -- same Fixes commit, same fix pattern, single backport unit for stable.
- Reworded changelog to cover both sites.

v2: https://lore.kernel.org/all/[email protected]/
v1: https://lore.kernel.org/all/[email protected]/

 mm/hugetlb.c | 2 ++
 1 file changed, 2 insertions(+)

mm/hugetlb.c +2 -0

index 4b80b167cc9c..ba7c3ed96835 100644
@@ -4974,6 +4974,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
 							    addr, dst_vma);
 				folio_put(pte_folio);
 				if (ret) {
+					restore_reserve_on_error(h, dst_vma, addr, new_folio);
 					folio_put(new_folio);
 					break;
 				}

@@ -6270,6 +6271,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
 		folio_put(*foliop);
 		*foliop = NULL;
 		if (ret) {
+			restore_reserve_on_error(h, dst_vma, dst_addr, folio);
 			folio_put(folio);
 			goto out;
 		}

Signature · 1 line

2.53.0

Muchun Song

maintainer Reviewed-by on v3 1/1

2026-05-20 06:16 UTC #3 lore raw

Re: [PATCH v3] mm/hugetlb: restore reservation on error in hugetlb folio copy paths

Quoted 27 lines · David Carlier

Two sites in mm/hugetlb.c allocate a hugetlb folio via alloc_hugetlb_folio() (consuming a VMA reservation) and then call copy_user_large_folio(), which became int-returning in commit 1cb9dc4b475c ("mm: hwpoison: support recovery from HugePage copy-on-write faults") and can now fail (e.g. -EHWPOISON on a hwpoisoned source page). On the failure path, folio_put() restores the global hugetlb pool count through free_huge_folio(), but the per-VMA reservation map entry is left marked consumed:
- hugetlb_mfill_atomic_pte() resubmission path (UFFDIO_COPY)
- copy_hugetlb_page_range() fork-time CoW path when hugetlb_try_dup_anon_rmap() fails (rare: pinned hugetlb anon folio under fork)
User-visible effect: on UFFDIO_COPY into a private hugetlb VMA where the resubmission copy fails, the reservation for that address is leaked from the VMA's reserve map. A subsequent fault at the same address takes the no-reservation path, and under hugetlb pool pressure the task is SIGBUSed at an address it had previously reserved. The fork-time CoW path leaks the same way in the child VMA's reserve map, though it requires the much rarer combination of pinned hugetlb anon page + hwpoisoned source.

Quoted 6 lines

Add the missing restore_reserve_on_error() call before folio_put() on both error paths.
Fixes 1cb9dc4b475c ("mm: hwpoison: support recovery from HugePage copy-on-write faults")
Cc <[email protected]>
Signed-off-by David Carlier <[email protected]>

Reviewed-by Muchun Song <[email protected]>

Thanks.