powerpc/pseries/iommu: Don't use dma_iommu_ops on secure guests

Secure guest memory is inacessible to devices so regular DMA isn't
possible.

In that case set devices' dma_map_ops to NULL so that the generic
DMA code path will use SWIOTLB to bounce buffers for DMA.
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190820021326.6884-14-bauerman@linux.ibm.com

arch/powerpc/platforms/pseries/iommu.c

@@ -36,6 +36,7 @@
 #include <asm/udbg.h>
 #include <asm/mmzone.h>
 #include <asm/plpar_wrappers.h>
+#include <asm/svm.h>
 
 #include "pseries.h"
 
@@ -1319,7 +1320,15 @@ void iommu_init_early_pSeries(void)
 	of_reconfig_notifier_register(&iommu_reconfig_nb);
 	register_memory_notifier(&iommu_mem_nb);
 
-	set_pci_dma_ops(&dma_iommu_ops);
+	/*
+	 * Secure guest memory is inacessible to devices so regular DMA isn't
+	 * possible.
+	 *
+	 * In that case keep devices' dma_map_ops as NULL so that the generic
+	 * DMA code path will use SWIOTLB to bounce buffers for DMA.
+	 */
+	if (!is_secure_guest())
+		set_pci_dma_ops(&dma_iommu_ops);
 }
 
 static int __init disable_multitce(char *str)