dma-direct: Make DIRECT_MAPPING_ERROR viable for SWIOTLB

With the overflow buffer removed, we no longer have a unique address
which is guaranteed not to be a valid DMA target to use as an error
token. The DIRECT_MAPPING_ERROR value of 0 tries to at least represent
an unlikely DMA target, but unfortunately there are already SWIOTLB
users with DMA-able memory at physical address 0 which now gets falsely
treated as a mapping failure and leads to all manner of misbehaviour.

The best we can do to mitigate that is flip DIRECT_MAPPING_ERROR to the
other commonly-used error value of all-bits-set, since the last single
byte of memory is by far the least-likely-valid DMA target.

Fixes: dff8d6c1ed58 ("swiotlb: remove the overflow buffer")
Reported-by: John Stultz <[email protected]>
Tested-by: John Stultz <[email protected]>
Acked-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: Robin Murphy <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
index bd73e7a9141076389ad638cc8fe4f48515331711..9e66bfe369aa057ac9d285d1f3cede42e54387cf 100644 (file)
--- a/include/linux/dma-direct.h
+++ b/include/linux/dma-direct.h
@@ -5,7 +5,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/mem_encrypt.h>
 
-#define DIRECT_MAPPING_ERROR           0
+#define DIRECT_MAPPING_ERROR           (~(dma_addr_t)0)
 
 #ifdef CONFIG_ARCH_HAS_PHYS_TO_DMA
 #include <asm/dma-direct.h>