iommu/dma: Don't remap CMA unnecessarily

Always remapping CMA allocations was largely a bodge to keep the freeing
logic manageable when it was split between here and an arch wrapper. Now
that it's all together and streamlined, we can relax that limitation.
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/dma-iommu.c

@@ -973,7 +973,6 @@ static void *iommu_dma_alloc(struct device *dev, size_t size,
 {
 	bool coherent = dev_is_dma_coherent(dev);
 	int ioprot = dma_info_to_prot(DMA_BIDIRECTIONAL, coherent, attrs);
-	pgprot_t prot = arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs);
 	size_t iosize = size;
 	struct page *page;
 	void *addr;
@@ -1021,6 +1020,9 @@ static void *iommu_dma_alloc(struct device *dev, size_t size,
 	if (*handle == DMA_MAPPING_ERROR)
 		goto out_free_pages;
 
+	if (!coherent || PageHighMem(page)) {
+		pgprot_t prot = arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs);
+
 		addr = dma_common_contiguous_remap(page, size, VM_USERMAP, prot,
 				__builtin_return_address(0));
 		if (!addr)
@@ -1028,6 +1030,9 @@ static void *iommu_dma_alloc(struct device *dev, size_t size,
 
 		if (!coherent)
 			arch_dma_prep_coherent(page, iosize);
+	} else {
+		addr = page_address(page);
+	}
 	memset(addr, 0, size);
 	return addr;
 out_unmap: