Now, all passthrough devices that should benefit from the nested SMMUv3
feature are assigned to dedicated pxb buses. So, the default PCI bus can
be only used by emulated devices.

In theory, these emualted devices can be still attached to an emualted
SMMUv3 instance, yet there is no gain doing that. Set the default PCI bus
to bypass iommu, for the maximum performance.

Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 hw/arm/virt.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 3610f53304..5e91dc8c3d 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1708,7 +1708,8 @@ static void create_pcie(VirtMachineState *vms)
     }
 
     pci = PCI_HOST_BRIDGE(dev);
-    pci->bypass_iommu = vms->default_bus_bypass_iommu;
+    /* Default bus used by emulated devices does not go through nested SMMUs */
+    pci->bypass_iommu = vms->default_bus_bypass_iommu || vms->num_nested_smmus;
     vms->bus = pci->bus;
     if (vms->bus) {
         pci_init_nic_devices(pci->bus, mc->default_nic);
-- 
2.43.0