+#ifdef CONFIG_SWIOTLB
+	struct io_tlb_mem	*dma_io_tlb_mem;
 #endif

Please add a new config option for this code instead of always building
it when swiotlb is enabled.

+static int swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
+				   size_t size)

Can you split the refactoring in swiotlb.c into one or more prep
patches?

+static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
+				    struct device *dev)
+{
+	struct io_tlb_mem *mem = rmem->priv;
+	int ret;
+
+	if (dev->dma_io_tlb_mem)
+		return -EBUSY;
+
+	if (!mem) {
+		mem = kzalloc(sizeof(*mem), GFP_KERNEL);
+		if (!mem)
+			return -ENOMEM;

What is the calling convention here that allows for a NULL and non-NULL
private data?