Re: [PATCH 6/6] pc: Allow instantiating a virtio-iommu device

[Eric Auger]

Hi Jean,

On 8/10/21 10:45 AM, Jean-Philippe Brucker wrote:
> From: Eric Auger <eric.auger@redhat.com>
>
> Add a hotplug handler for virtio-iommu on x86 and set the necessary
> reserved region property. On x86, the [0xfee00000, 0xfeefffff] DMA
> region is reserved for MSIs. DMA transactions to this range either
> trigger IRQ remapping in the IOMMU or bypasses IOMMU translation.
>
> Although virtio-iommu does not support IRQ remapping it must be informed
> of the reserved region so that it can forward DMA transactions targeting
> this region.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>

I think we need to handle the case where the end-user gets lost with
iommu options and use an invalid combination such as

-M q35,iommu=on,int_remap=on,kernel_irqchip=off -device -device virtio-iommu-pci

We may also document somewhere that the virtio-iommu-pci
does not support irq remapping as this may be an important limitation on x86.

Thanks

Eric

> ---
>  hw/i386/pc.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 694fc9ce07..fb24f000e7 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1376,6 +1376,14 @@ static void 
> pc_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_PMEM_PCI) ||
>                 object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
>          pc_virtio_md_pci_pre_plug(hotplug_dev, dev, errp);
> +    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
> +        /* Declare the reserved MSI region */
> +        char *resv_prop_str = g_strdup_printf("0xfee00000:0xfeefffff:%d",
> +                                              VIRTIO_IOMMU_RESV_MEM_T_MSI);
> +
> +        qdev_prop_set_uint32(dev, "len-reserved-regions", 1);
> +        qdev_prop_set_string(dev, "reserved-regions[0]", resv_prop_str);
> +        g_free(resv_prop_str);
>      }
>  }
>  
> @@ -1436,7 +1444,8 @@ static HotplugHandler 
> *pc_get_hotplug_handler(MachineState *machine,
>      if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM) ||
>          object_dynamic_cast(OBJECT(dev), TYPE_CPU) ||
>          object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_PMEM_PCI) ||
> -        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
> +        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI) ||
> +        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
>          return HOTPLUG_HANDLER(machine);
>      }
>