[PATCH 2/2] swiotlb: Skip cache maintenance on map error

[Robin Murphy <robin.murphy@arm.com>]

If swiotlb_bounce_page() failed, calling arch_sync_dma_for_device() may
lead to such delights as performing cache maintenance on whatever
address phys_to_virt(SWIOTLB_MAP_ERROR) looks like, which is typically
outside the kernel memory map and goes about as well as expected.

Don't do that.

Fixes: a4a4330db46a ("swiotlb: add support for non-coherent DMA")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 kernel/dma/swiotlb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 5731daa09a32..045930e32c0e 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -679,7 +679,8 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
 	}
 
 	if (!dev_is_dma_coherent(dev) &&
-	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
+	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0 &&
+	    dev_addr != DIRECT_MAPPING_ERROR)
 		arch_sync_dma_for_device(dev, phys, size, dir);
 
 	return dev_addr;
-- 
2.19.1.dirty