iommu/amd: Don't clear DTE flags when modifying it

During device assignment/deassignment the flags in the DTE
get lost, which might cause spurious faults, for example
when the device tries to access the system management range.
Fix this by not clearing the flags with the rest of the DTE.

Reported-by: G. Richard Bellamy <rbellamy@pteradigm.com>
Tested-by: G. Richard Bellamy <rbellamy@pteradigm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Joerg Roedel <jroedel@suse.de>
diff --git a/drivers/iommu/amd_iommu_types.h b/drivers/iommu/amd_iommu_types.h
index f659088..c9b6472 100644
--- a/drivers/iommu/amd_iommu_types.h
+++ b/drivers/iommu/amd_iommu_types.h
@@ -295,6 +295,7 @@
 #define IOMMU_PTE_IR (1ULL << 61)
 #define IOMMU_PTE_IW (1ULL << 62)
 
+#define DTE_FLAG_MASK	(0x3ffULL << 32)
 #define DTE_FLAG_IOTLB	(0x01UL << 32)
 #define DTE_FLAG_GV	(0x01ULL << 55)
 #define DTE_GLX_SHIFT	(56)