mm-damon-vaddr-avoid-hw-driven-pte-updates-during-damon_hugetlb_mkold.patch removed from -mm tree

The quilt patch titled
Subject: mm/damon/vaddr: avoid hw-driven pte updates during damon_hugetlb_mkold()
has been removed from the -mm tree. Its filename was
mm-damon-vaddr-avoid-hw-driven-pte-updates-during-damon_hugetlb_mkold.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: SJ Park <[email protected]>
Subject: mm/damon/vaddr: avoid hw-driven pte updates during damon_hugetlb_mkold()
Date: Mon, 7 Sep 2026 10:03:56 -0700

damon_hugetlb_mkold() reads the page table entry into a local variable, unsets the accessed bit in the variable, and updates the page table entry with the updated variable value. If hardware updates the same page table entry in parallel, the hw updates could be lost. For example, hardware-updated dirty bits might be lost.

Avoid the parallel updates by clearing the page table entry when reading it together, using huge_ptep_get_and_clear(). If a parallel write to the memory is made after the clearing, the hw will see the page table entry is cleared, trigger page fault and wait until it is handled. The page fault handling will wait for damon_hugetlb_mkold() due to the page table lock.

Because hugetlbfs is an in-memory file system and hugetlb pages cannot be reclaimed, no critical issue is expected to my best knowledge. But definitely this is a nasty bug that should be fixed sooner rather than later.

The issue was discovered [1] by Sashiko.

---

 mm/damon/vaddr.c |   21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

@@ -293,22 +293,29 @@ out:
 }
 
 #ifdef CONFIG_HUGETLB_PAGE
+static bool damon_hugetlb_ptep_mkold(pte_t *pte, struct mm_struct *mm,
+		struct vm_area_struct *vma, unsigned long addr, pte_t *entry)
+{
+	unsigned long psize = huge_page_size(hstate_vma(vma));
+
+	if (!pte_young(*entry))
+		return false;
+	*entry = huge_ptep_get_and_clear(mm, addr, pte, psize);
+	*entry = pte_mkold(*entry);
+	set_huge_pte_at(mm, addr, pte, *entry, psize);
+	return true;
+}
+
 static void damon_hugetlb_mkold(pte_t *pte, struct mm_struct *mm,
 				struct vm_area_struct *vma, unsigned long addr)
 {
 	bool referenced = false;
 	pte_t entry = huge_ptep_get(mm, addr, pte);
 	struct folio *folio = pfn_folio(pte_pfn(entry));
-	unsigned long psize = huge_page_size(hstate_vma(vma));
 
 	folio_get(folio);
 
-	if (pte_young(entry)) {
-		referenced = true;
-		entry = pte_mkold(entry);
-		set_huge_pte_at(mm, addr, pte, entry, psize);
-	}
-
+	referenced = damon_hugetlb_ptep_mkold(pte, mm, vma, addr, &entry);
 	if (mmu_notifier_clear_young(mm, addr,
 				     addr + huge_page_size(hstate_vma(vma))))
 		referenced = true;

_

Patches currently in -mm which might be from [email protected] are

mm-damon-core-dont-skip-damos_adjust_quota-while-esz-is-not-zero.patch mm-damon-core-skip-applying-scheme-if-region-split-for-quota-fails.patch mm-damon-paddr-respect-folio-end-for-damos_stat.patch mm-damon-paddr-respect-folio-end-for-damos-actions-except-stat.patch mm-damon-vaddr-respect-folio-end-for-damos_stat.patch mm-damon-vaddr-respect-folio-end-for-damos_migrate_hotcold.patch mm-damon-core-handle-extreme-memory-state-in-damon_get_node_mem_bp.patch mm-damon-core-handle-extreme-memory-state-in-get_node_memcg_used_bp.patch mm-damon-core-handle-extreme-memory-state-in-get_in_active_mem_bp.patch mm-damon-core-introduce-damon_filter_type_pgidle_unset.patch mm-damon-paddr-support-pgidle_unset-probe-filter-type.patch mm-damon-sysfs-support-pgidle_unset-probe-filter-type.patch docs-mm-damon-design-document-pgidle_unset-probe-filter-type.patch mm-damon-core-introduce-damon_prep-struct.patch mm-damon-core-commit-preps.patch mm-damon-core-introduce-damon_operations-prep_probes.patch mm-damon-paddr-support-damon_prep.patch mm-damon-sysfs-implement-preps-directory.patch mm-damon-sysfs-implement-preps-nr_preps-file.patch mm-damon-sysfs-create-directories-for-nr_preps-writes.patch mm-damon-sysfs-implement-prep_action-file.patch mm-damon-sysfs-pass-preps-to-damon-core.patch selftests-damon-sysfssh-test-probe-prep-sysfs-files.patch docs-mm-damon-design-document-probe-preps.patch docs-admin-guide-mm-damon-usage-document-probe-preps-sysfs-files.patch docs-abi-damon-document-probe-prep-sysfs-files.patch mm-damon-tests-core-kunit-test-committing-psi-goal-to-psi-goal.patch mm-damon-core-handle-uninitialized-damos_quota_goal-last_psi_total.patch mm-damon-core-copy-nid-for-eligible_mem_bp-damos-quota-goal-commit.patch mm-damon-sysfs-set-next-refresh-jiffies-per-sysfs-context.patch mm-damon-tests-core-kunit-test-damon_commit_filter.patch mm-damon-tests-core-kunit-add-damon_commit_probes-test.patch selftests-damon-_damon_sysfs-implement-damonprobes.patch selftests-damon-drgn_dump_damon_status-dump-probes.patch selftests-damon-sysfspy-extend-commit-assertion-function-for-probes.patch selftests-damon-sysfspy-test-damon-probes.patch mm-damon-core-use-damon_nr_samples_per_aggr-for-max-merge-threshold.patch mm-damon-core-remove-debug-messages.patch mm-damon-core-remove-debug-messages-fix.patch mm-damon-vaddr-remove-a-debug-message.patch mm-damon-core-validate-number-of-probes-in-valid_probe_params.patch mm-damon-sysfs-remove-probes-number-validation.patch mm-damon-tests-core-kunit-extend-set_regions-test-for-error-case.patch mm-damon-tests-core-kunit-test-=0-size-damon_set_regions-inputs.patch mm-damon-tests-core-kunit-test-overlapping-ranges-for-set_regions.patch mm-damon-tests-core-kunit-test-damon_nr_samples_per_aggr.patch selftests-damon-sysfssh-test-hugepage_mem_bp-quota-goal.patch docs-mm-damon-maintainer-profile-update-ai-review-for-sashiko-replies.patch docs-abi-damon-recommend-subsystem-doc-instead-of-admin-guide.patch mm-damon-core-error-damos_commit_quota_goal-for-zero-target_value.patch revert-mm-damon-lru_sort-error-out-for-10000-active_mem_bp.patch revert-samples-damon-mtier-error-out-for-zero-quota-goal-target-values.patch mm-damon-core-handle-null-ctx-parameter-in-damon_call.patch mm-damon-core-set-ctx-call_controls_obsolete-in-damon_new_ctx.patch mm-damon-reclaim-remove-unnecessary-damon_call-param-validation.patch mm-damon-lru_sort-remove-unnecessary-damon_call-param-validation.patch mm-damon-vaddr-support-prep_probes.patch mm-damon-paddr-move-probe-filter-handling-to-ops-common.patch mm-damon-vaddr-support-apply_probe.patch mm-damon-vaddr-extend-apply_probes-for-hugetlb.patch mm-damon-vaddr-support-pgidle_unset-probe-filter-type.patch mm-damon-api-introduce-damon_filter_type_pgidle_set.patch mm-damon-paddr-support-damon_filter_type_pgidle_set.patch mm-damon-vaddr-support-damon_filter_type_pgidle_set.patch mm-damon-sysfs-support-damon_filter_type_pgidle_set.patch docs-mm-damon-design-update-for-pgidle_set-probe-filter.patch mm-damon-api-introduce-damos_filter_type_probe_hits_wsum.patch mm-damon-api-introduce-damos_filter_type_probe_hits_wsum-fix.patch mm-damon-core-extend-probe_hits_wsum-for-moving-sum-based-calculation.patch mm-damon-core-support-probe_hits_wsum-damos-core-filter.patch mm-damon-sysfs-schemes-rename-sysfs_filter-sz_range-to-range_minmax.patch mm-damon-sysfs-schemes-support-probe_hits_wsum-damos-core-filter.patch docs-mm-damon-design-update-for-probe_hits_wsum-damos-core-filter.patch docs-admin-guide-mm-damon-usage-update-for-probe_hits_wsum-damos-filter.patch mm-damon-sysfs-schemes-read-sysfs_filter-addr_range-only-once.patch mm-damon-sysfs-schemes-read-sysfs_filter-sz_range-only-once.patch mm-damon-core-return-an-error-from-damos_commit_filter_arg.patch mm-damon-core-disallow-max-min-damos-filter-range-arguments-commit.patch mm-damon-sysfs-schemes-drop-centralized-filter-range-arg-validations.patch mm-damon-sysfs-schemes-use-switch-case-in-add_scheme_filters.patch mm-damon-core-kunit-extend-damos_commit_filter_for-for-wrong-input.patch mm-damon-core-kunit-test-invalid-damos-filter-commits.patch mm-damon-api-introduce-damon_filter_type_hugepage_size.patch mm-damon-core-commit-hugepage_size-type-damon-filter.patch mm-damon-ops-common-support-hugepage_size-damon-filter-matching.patch mm-damon-sysfs-add-minmax-files-under-probe-filter-directory.patch mm-damon-sysfs-support-hugepage_size-probe-filter.patch docs-mm-damon-design-update-for-hugepage_size-probe-filter.patch docs-admin-guide-mm-damon-usage-update-for-hugepage_size.patch docs-abi-damon-update-for-hugepage_size-probe-filter.patch mm-damon-api-remove-nr_damos_filter_types.patch mm-damon-core-use-abs_diff-in-damon_feed_loop_next_input.patch mm-damon-core-use-mult_frac-in-damon_feed_loop_next_input.patch mm-damon-core-set-damon_ctx-walk_control_obsolete-in-damon_new_ctx.patch mm-damon-core-document-damon_call-damon_start-race-hang-issue.patch mm-damon-paddr-remove-pa-parameter-from-damon_pa_filter_pass.patch mm-damon-tests-core-kunit-test-eligible_mem_bp-commitment.patch mm-damon-tests-core-kunit-add-probe_hits_wsum-damos-filter-commit-test.patch selftests-damon-sysfs_memcg_path_leak-fail-only-for-real-damon-leak.patch docs-mm-damon-design-clarify-bp-is-basis-point.patch