amd-iommu: disable round-robin allocator for CONFIG_IOMMU_STRESS

Disabling the round-robin allocator results in reusing the same
dma-addresses again very fast. This is a good test if the iotlb flushing
is working correctly.
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

arch/x86/kernel/amd_iommu.c

@@ -783,6 +783,11 @@ static unsigned long dma_ops_alloc_addresses(struct device *dev,
 {
 	unsigned long address;
 
+#ifdef CONFIG_IOMMU_STRESS
+	dom->next_address = 0;
+	dom->need_flush = true;
+#endif
+
 	address = dma_ops_area_alloc(dev, dom, pages, align_mask,
 				     dma_mask, dom->next_address);