[PATCH 14/24] iommu/dma: Don't remap CMA unnecessarily

[Christoph Hellwig]

From: Robin Murphy <robin.murphy@xxxxxxx>

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@xxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 drivers/iommu/dma-iommu.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 4134f13b5529..cffd30810d41 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/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;
@@ -1021,13 +1020,19 @@ static void *iommu_dma_alloc(struct device *dev, size_t size,
 	if (*handle == DMA_MAPPING_ERROR)
 		goto out_free_pages;
 
-	addr = dma_common_contiguous_remap(page, size, VM_USERMAP, prot,
-			__builtin_return_address(0));
-	if (!addr)
-		goto out_unmap;
+	if (!coherent || PageHighMem(page)) {
+		pgprot_t prot = arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs);
 
-	if (!coherent)
-		arch_dma_prep_coherent(page, iosize);
+		addr = dma_common_contiguous_remap(page, size, VM_USERMAP, prot,
+				__builtin_return_address(0));
+		if (!addr)
+			goto out_unmap;
+
+		if (!coherent)
+			arch_dma_prep_coherent(page, iosize);
+	} else {
+		addr = page_address(page);
+	}
 	memset(addr, 0, size);
 	return addr;
 out_unmap:
-- 
2.20.1