Merge tag 'dma-mapping-6.19-2026-01-20' of git://git.kernel.org/pub/scm/linux/kernel/git/mszyprowski/linux

Pull dma-mapping fixes from Marek Szyprowski:

 - minor fixes for the corner cases of the SWIOTLB pool management
   (Robin Murphy)

* tag 'dma-mapping-6.19-2026-01-20' of git://git.kernel.org/pub/scm/linux/kernel/git/mszyprowski/linux:
  dma/pool: Avoid allocating redundant pools
  mm_zone: Generalise has_managed_dma()
  dma/pool: Improve pool lookup

3 files changed, 25 insertions, 19 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 75ef7c9f9307..fc5d6c88d2f0 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1648,14 +1648,15 @@ static inline int is_highmem(const struct zone *zone)
 	return is_highmem_idx(zone_idx(zone));
 }
 
-#ifdef CONFIG_ZONE_DMA
-bool has_managed_dma(void);
-#else
+bool has_managed_zone(enum zone_type zone);
 static inline bool has_managed_dma(void)
 {
+#ifdef CONFIG_ZONE_DMA
+	return has_managed_zone(ZONE_DMA);
+#else
 	return false;
-}
 #endif
+}
 
 
 #ifndef CONFIG_NUMA
diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 26392badc36b..c5da29ad010c 100644
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -184,6 +184,12 @@ static __init struct gen_pool *__dma_atomic_pool_init(size_t pool_size,
 	return pool;
 }
 
+#ifdef CONFIG_ZONE_DMA32
+#define has_managed_dma32 has_managed_zone(ZONE_DMA32)
+#else
+#define has_managed_dma32 false
+#endif
+
 static int __init dma_atomic_pool_init(void)
 {
 	int ret = 0;
@@ -199,17 +205,20 @@ static int __init dma_atomic_pool_init(void)
 	}
 	INIT_WORK(&atomic_pool_work, atomic_pool_work_fn);
 
-	atomic_pool_kernel = __dma_atomic_pool_init(atomic_pool_size,
+	/* All memory might be in the DMA zone(s) to begin with */
+	if (has_managed_zone(ZONE_NORMAL)) {
+		atomic_pool_kernel = __dma_atomic_pool_init(atomic_pool_size,
 						    GFP_KERNEL);
-	if (!atomic_pool_kernel)
-		ret = -ENOMEM;
+		if (!atomic_pool_kernel)
+			ret = -ENOMEM;
+	}
 	if (has_managed_dma()) {
 		atomic_pool_dma = __dma_atomic_pool_init(atomic_pool_size,
 						GFP_KERNEL | GFP_DMA);
 		if (!atomic_pool_dma)
 			ret = -ENOMEM;
 	}
-	if (IS_ENABLED(CONFIG_ZONE_DMA32)) {
+	if (has_managed_dma32) {
 		atomic_pool_dma32 = __dma_atomic_pool_init(atomic_pool_size,
 						GFP_KERNEL | GFP_DMA32);
 		if (!atomic_pool_dma32)
@@ -224,11 +233,11 @@ postcore_initcall(dma_atomic_pool_init);
 static inline struct gen_pool *dma_guess_pool(struct gen_pool *prev, gfp_t gfp)
 {
 	if (prev == NULL) {
-		if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp & GFP_DMA32))
-			return atomic_pool_dma32;
-		if (atomic_pool_dma && (gfp & GFP_DMA))
-			return atomic_pool_dma;
-		return atomic_pool_kernel;
+		if (gfp & GFP_DMA)
+			return atomic_pool_dma ?: atomic_pool_dma32 ?: atomic_pool_kernel;
+		if (gfp & GFP_DMA32)
+			return atomic_pool_dma32 ?: atomic_pool_dma ?: atomic_pool_kernel;
+		return atomic_pool_kernel ?: atomic_pool_dma32 ?: atomic_pool_dma;
 	}
 	if (prev == atomic_pool_kernel)
 		return atomic_pool_dma32 ? atomic_pool_dma32 : atomic_pool_dma;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f65c4edf199d..cbf758e27aa2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7457,20 +7457,16 @@ bool put_page_back_buddy(struct page *page)
 }
 #endif
 
-#ifdef CONFIG_ZONE_DMA
-bool has_managed_dma(void)
+bool has_managed_zone(enum zone_type zone)
 {
 	struct pglist_data *pgdat;
 
 	for_each_online_pgdat(pgdat) {
-		struct zone *zone = &pgdat->node_zones[ZONE_DMA];
-
-		if (managed_zone(zone))
+		if (managed_zone(&pgdat->node_zones[zone]))
 			return true;
 	}
 	return false;
 }
-#endif /* CONFIG_ZONE_DMA */
 
 #ifdef CONFIG_UNACCEPTED_MEMORY