Re: [PATCH v3 04/10] hw/arm/virt: Reject instantiation of multiple IOMMUs

[Igor Mammedov]

On Tue, 14 Sep 2021 15:19:59 +0100
Jean-Philippe Brucker <jean-philippe@linaro.org> 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.
> 
> Fixes: 70e89132c9 ("hw/arm/virt: Add the virtio-iommu device tree mappings")
> Reviewed-by: Eric Auger <eric.auger@redhat.com>
> 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 f238766aa1..26069f943a 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -2471,6 +2471,11 @@ 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;
> +        }

can you move check into 'pre_plug' callback?

(plug should not fail and just finish up whatever was
verified/set by pre_plug, there are plans to remove errp
argument from 'plug' callback)
> +
>          vms->iommu = VIRT_IOMMU_VIRTIO;
>          vms->virtio_iommu_bdf = pci_get_bdf(pdev);
>          create_virtio_iommu_dt_bindings(vms);