[PATCH 4.14 05/72] arm64: dma-mapping: Fix FORCE_CONTIGUOUS buffer clearing

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Robin Murphy <robin.murphy@xxxxxxx>

commit 3238c359acee4ab57f15abb5a82b8ab38a661ee7 upstream.

We need to invalidate the caches *before* clearing the buffer via the
non-cacheable alias, else in the worst case __dma_flush_area() may
write back dirty lines over the top of our nice new zeros.

Fixes: dd65a941f6ba ("arm64: dma-mapping: clear buffers allocated with FORCE_CONTIGUOUS flag")
Cc: <stable@xxxxxxxxxxxxxxx> # 4.18.x-
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/arm64/mm/dma-mapping.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -633,9 +633,9 @@ static void *__iommu_alloc_attrs(struct
 						   prot,
 						   __builtin_return_address(0));
 		if (addr) {
-			memset(addr, 0, size);
 			if (!coherent)
 				__dma_flush_area(page_to_virt(page), iosize);
+			memset(addr, 0, size);
 		} else {
 			iommu_dma_unmap_page(dev, *handle, iosize, 0, attrs);
 			dma_release_from_contiguous(dev, page,