iommu/dma: Remove broken huge page handling

The attempt to handle huge page allocations was originally added since
the comments around stripping __GFP_COMP in other implementations were
nonsensical, and we naively assumed that split_huge_page() could simply
be called equivalently to split_page(). It turns out that this doesn't
actually work correctly, so just get rid of it - there's little point
going to the effort of allocating huge pages if we're only going to
split them anyway.
Reported-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/e287dbe69aa0933abafd97c80631940fd188ddd1.1599132844.git.robin.murphy@arm.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/dma-iommu.c

@@ -524,6 +524,9 @@ static struct page **__iommu_dma_alloc_pages(struct device *dev,
 	/* IOMMU can map any pages, so himem can also be used here */
 	gfp |= __GFP_NOWARN | __GFP_HIGHMEM;
 
+	/* It makes no sense to muck about with huge pages */
+	gfp &= ~__GFP_COMP;
+
 	while (count) {
 		struct page *page = NULL;
 		unsigned int order_size;
@@ -544,15 +547,9 @@ static struct page **__iommu_dma_alloc_pages(struct device *dev,
 			page = alloc_pages_node(nid, alloc_flags, order);
 			if (!page)
 				continue;
-			if (!order)
-				break;
-			if (!PageCompound(page)) {
+			if (order)
 				split_page(page, order);
-				break;
-			} else if (!split_huge_page(page)) {
-				break;
-			}
-			__free_pages(page, order);
+			break;
 		}
 		if (!page) {
 			__iommu_dma_free_pages(pages, i);