Re: [PATCH v8 4/8] virtio-iommu: set supported page size mask

[Auger Eric <eric.auger@redhat.com>]

Hi Bharat,

On 3/18/20 11:11 AM, Bharat Bhushan wrote:
> Add optional interface to set page size mask.
> Currently this is set global configuration and not
> per endpoint.
> 
> Signed-off-by: Bharat Bhushan <bbhushan2@marvell.com>
> ---
> v7->v8:
>  - new patch
> 
>  hw/virtio/virtio-iommu.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c
> index 4cee8083bc..c00a55348d 100644
> --- a/hw/virtio/virtio-iommu.c
> +++ b/hw/virtio/virtio-iommu.c
> @@ -650,6 +650,15 @@ static gint int_cmp(gconstpointer a, gconstpointer b, gpointer user_data)
>      return (ua > ub) - (ua < ub);
>  }
>  
> +static void virtio_iommu_set_page_size_mask(IOMMUMemoryRegion *mr,
> +                                            uint64_t page_size_mask)
> +{
> +    IOMMUDevice *sdev = container_of(mr, IOMMUDevice, iommu_mr);
> +    VirtIOIOMMU *s = sdev->viommu;
> +
> +    s->config.page_size_mask = page_size_mask;
The problem is page_size_mask is global to the VIRTIO-IOMMU.

- Can't different VFIO containers impose different/inconsistent settings?
- VFIO devices can be hotplugged. So we may start with some default
page_size_mask which is latter overriden by a host imposed one. Assume
you first launch the VM with a virtio NIC. This uses 64K. Then you
hotplug a VFIO device behind a physical IOMMU which only supports 4K
pages. Isn't it a valid scenario?

Thanks

Eric

> +}
> +
>  static void virtio_iommu_device_realize(DeviceState *dev, Error **errp)
>  {
>      VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> @@ -865,6 +874,7 @@ static void virtio_iommu_memory_region_class_init(ObjectClass *klass,
>      IOMMUMemoryRegionClass *imrc = IOMMU_MEMORY_REGION_CLASS(klass);
>  
>      imrc->translate = virtio_iommu_translate;
> +    imrc->iommu_set_page_size_mask = virtio_iommu_set_page_size_mask;
>  }
>  
>  static const TypeInfo virtio_iommu_info = {
>