+ mm-damon-core-disallow-non-power-of-two-min_region_sz-on-damon_start.patch added to mm-hotfixes-unstable branch

+ mm-damon-core-disallow-non-power-of-two-min_region_sz-on-damon_start.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/damon/core: disallow non-power of two min_region_sz on damon_start()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-damon-core-disallow-non-power-of-two-min_region_sz-on-damon_start.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-core-disallow-non-power-of-two-min_region_sz-on-damon_start.patch

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

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------------------------------------------------------
From: SeongJae Park <sj@kernel.org>
Subject: mm/damon/core: disallow non-power of two min_region_sz on damon_start()
Date: Sat, 11 Apr 2026 14:36:36 -0700

Commit d8f867fa0825 ("mm/damon: add damon_ctx->min_sz_region") introduced
a bug that allows unaligned DAMON region address ranges.  Commit
c80f46ac228b ("mm/damon/core: disallow non-power of two min_region_sz")
fixed it, but only for damon_commit_ctx() use case.  Still, DAMON sysfs
interface can emit non-power of two min_region_sz via damon_start().  Fix
the path by adding the is_power_of_2() check on damon_start().

The issue was discovered by sashiko [1].

Link: https://lore.kernel.org/20260411213638.77768-1-sj@kernel.org
Link: https://lore.kernel.org/20260403155530.64647-1-sj@kernel.org [1]
Fixes: d8f867fa0825 ("mm/damon: add damon_ctx->min_sz_region")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.18.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/damon/core.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/mm/damon/core.c~mm-damon-core-disallow-non-power-of-two-min_region_sz-on-damon_start
+++ a/mm/damon/core.c
@@ -1368,6 +1368,11 @@ int damon_start(struct damon_ctx **ctxs,
 	int i;
 	int err = 0;
 
+	for (i = 0; i < nr_ctxs; i++) {
+		if (!is_power_of_2(ctxs[i]->min_region_sz))
+			return -EINVAL;
+	}
+
 	mutex_lock(&damon_lock);
 	if ((exclusive && nr_running_ctxs) ||
 			(!exclusive && running_exclusive_ctxs)) {
_

Patches currently in -mm which might be from sj@kernel.org are

mm-damon-core-disallow-time-quota-setting-zero-esz.patch
mm-damon-core-disallow-non-power-of-two-min_region_sz-on-damon_start.patch
mm-damon-core-fix-damon_call-vs-kdamond_fn-exit-race.patch
mm-damon-core-fix-damos_walk-vs-kdamond_fn-exit-race.patch
mm-damon-core-validate-damos_quota_goal-nid-for-node_mem_usedfree_bp.patch
mm-damon-core-validate-damos_quota_goal-nid-for-node_memcg_usedfree_bp.patch
mm-damon-core-use-time_in_range_open-for-damos-quota-window-start.patch
docs-admin-guide-mm-damon-reclaim-warn-commit_inputs-vs-param-updates-race.patch
docs-admin-guide-mm-damon-lru_sort-warn-commit_inputs-vs-param-updates-race.patch