powerpc/powernv/ioda: Fix endianness when reading TCEs

The iommu_table_ops::exchange() callback writes new TCE to the table and
returns old value and permission mask. The old TCE value is correctly
converted from BE to CPU endian; however permission mask was calculated
from BE value and therefore always returned DMA_NONE which could cause
memory leak on LE systems using VFIO SPAPR TCE IOMMU v1 driver.

This fixes pnv_tce_xchg() to have @oldtce a CPU endian.

Fixes: 05c6cfb9dce0 ("powerpc/iommu/powernv: Release replaced TCE")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/pci.c

@@ -737,8 +737,8 @@ int pnv_tce_xchg(struct iommu_table *tbl, long index,
 	if (newtce & TCE_PCI_WRITE)
 		newtce |= TCE_PCI_READ;
 
-	oldtce = xchg(pnv_tce(tbl, idx), cpu_to_be64(newtce));
-	*hpa = be64_to_cpu(oldtce) & ~(TCE_PCI_READ | TCE_PCI_WRITE);
+	oldtce = be64_to_cpu(xchg(pnv_tce(tbl, idx), cpu_to_be64(newtce)));
+	*hpa = oldtce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
 	*direction = iommu_tce_direction(oldtce);
 
 	return 0;