linux-kernel - [PATCH v1 4/5] mm: Take into account hierarchical percpu tree items for static mm

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Message-Id: <20251221232926.450602-5-mathieu.desnoyers@efficios.com>
Date: Sun, 21 Dec 2025 18:29:25 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Mark Brown <broonie@...nel.org>,
	linux-mm@...ck.org
Subject: [PATCH v1 4/5] mm: Take into account hierarchical percpu tree items for static mm_struct definitions

Both init_mm and efi_mm static definitions need to make room for the
hierarchical percpu counters items.

This fixes possible out-of-bounds accesses to init_mm and efi_mm.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mark Brown <broonie@...nel.org>
Cc: linux-mm@...ck.org
---
 include/linux/mm_types.h            |  6 ++--
 include/linux/percpu_counter_tree.h | 51 +++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index aefa64db3499..234374c46b71 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1366,9 +1366,9 @@ static inline void __mm_flags_set_mask_bits_word(struct mm_struct *mm,
 			 MT_FLAGS_USE_RCU)
 extern struct mm_struct init_mm;
 
-#define MM_STRUCT_FLEXIBLE_ARRAY_INIT				\
-{								\
-	[0 ... sizeof(cpumask_t) + MM_CID_STATIC_SIZE - 1] = 0	\
+#define MM_STRUCT_FLEXIBLE_ARRAY_INIT									\
+{													\
+	[0 ... sizeof(cpumask_t) + MM_CID_STATIC_SIZE + PERCPU_COUNTER_TREE_ITEMS_STATIC_SIZE - 1] = 0	\
 }
 
 /* Pointer magic because the dynamic array size confuses some compilers. */
diff --git a/include/linux/percpu_counter_tree.h b/include/linux/percpu_counter_tree.h
index 0daf09e08111..2e8b1ce5cd13 100644
--- a/include/linux/percpu_counter_tree.h
+++ b/include/linux/percpu_counter_tree.h
@@ -10,6 +10,52 @@
 
 #ifdef CONFIG_SMP
 
+#if NR_CPUS == (1U << 0)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	0
+#elif NR_CPUS <= (1U << 1)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	1
+#elif NR_CPUS <= (1U << 2)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	3
+#elif NR_CPUS <= (1U << 3)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	7
+#elif NR_CPUS <= (1U << 4)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	7
+#elif NR_CPUS <= (1U << 5)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	11
+#elif NR_CPUS <= (1U << 6)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	21
+#elif NR_CPUS <= (1U << 7)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	21
+#elif NR_CPUS <= (1U << 8)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	37
+#elif NR_CPUS <= (1U << 9)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	73
+#elif NR_CPUS <= (1U << 10)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	149
+#elif NR_CPUS <= (1U << 11)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	293
+#elif NR_CPUS <= (1U << 12)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	585
+#elif NR_CPUS <= (1U << 13)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	1173
+#elif NR_CPUS <= (1U << 14)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	2341
+#elif NR_CPUS <= (1U << 15)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	4681
+#elif NR_CPUS <= (1U << 16)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	4681
+#elif NR_CPUS <= (1U << 17)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	8777
+#elif NR_CPUS <= (1U << 18)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	17481
+#elif NR_CPUS <= (1U << 19)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	34953
+#elif NR_CPUS <= (1U << 20)
+# define PERCPU_COUNTER_TREE_STATIC_NR_ITEMS	69905
+#else
+# error "Unsupported number of CPUs."
+#endif
+
 struct percpu_counter_tree_level_item {
 	atomic_t count;			/*
 					 * Count the number of carry fort this tree item.
@@ -18,6 +64,9 @@ struct percpu_counter_tree_level_item {
 					 */
 } ____cacheline_aligned_in_smp;
 
+#define PERCPU_COUNTER_TREE_ITEMS_STATIC_SIZE	\
+	(PERCPU_COUNTER_TREE_STATIC_NR_ITEMS * sizeof(struct percpu_counter_tree_level_item))
+
 struct percpu_counter_tree {
 	/* Fast-path fields. */
 	unsigned int __percpu *level0;	/* Pointer to per-CPU split counters (tree level 0). */
@@ -92,6 +141,8 @@ int percpu_counter_tree_approximate_sum(struct percpu_counter_tree *counter)
 
 #else	/* !CONFIG_SMP */
 
+#define PERCPU_COUNTER_TREE_ITEMS_STATIC_SIZE	0
+
 struct percpu_counter_tree_level_item;
 
 struct percpu_counter_tree {
-- 
2.39.5