We do not support instantiating multiple IOMMUs. Before adding a
virtio-iommu, check that no other IOMMU is present. This will detect
both "iommu=smmuv3" machine parameter and another virtio-iommu instance.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
---
 hw/arm/virt.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index b4598d3fe6..5ca225291f 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -2475,6 +2475,11 @@ static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
     if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
         PCIDevice *pdev = PCI_DEVICE(dev);
 
+        if (vms->iommu != VIRT_IOMMU_NONE) {
+            error_setg(errp, "virt machine does not support multiple IOMMUs");
+            return;
+        }
+
         vms->iommu = VIRT_IOMMU_VIRTIO;
         vms->virtio_iommu_bdf = pci_get_bdf(pdev);
         create_virtio_iommu_dt_bindings(vms);
-- 
2.33.0

Hi Jean,
On 9/3/21 4:32 PM, Jean-Philippe Brucker wrote:
> We do not support instantiating multiple IOMMUs. Before adding a
> virtio-iommu, check that no other IOMMU is present. This will detect
> both "iommu=smmuv3" machine parameter and another virtio-iommu instance.
>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>

You may add
Fixes: 70e89132c9 ("hw/arm/virt: Add the virtio-iommu device tree mappings")
as the problem already exists with dt.

Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric
> ---
>  hw/arm/virt.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index b4598d3fe6..5ca225291f 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -2475,6 +2475,11 @@ static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
>      if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
>          PCIDevice *pdev = PCI_DEVICE(dev);
>  
> +        if (vms->iommu != VIRT_IOMMU_NONE) {
> +            error_setg(errp, "virt machine does not support multiple IOMMUs");
> +            return;
> +        }
> +
>          vms->iommu = VIRT_IOMMU_VIRTIO;
>          vms->virtio_iommu_bdf = pci_get_bdf(pdev);
>          create_virtio_iommu_dt_bindings(vms);