Re: [Qemu-devel] [PATCH] virtio: force VIRTIO_F_IOMMU_PLATFORM

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jan 17, 2017 at 12:01:00PM +0800, Jason Wang wrote:
> We allow vhost to clear VIRITO_F_IOMMU_PLATFORM which is wrong since
> VIRTIO_F_IOMMU_PLATFORM is mandatory for security. Fixing this by
> enforce it after vdc->get_features().
> 
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  hw/virtio/virtio-bus.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
> index d31cc00..a886011 100644
> --- a/hw/virtio/virtio-bus.c
> +++ b/hw/virtio/virtio-bus.c
> @@ -47,6 +47,7 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, Error **errp)
>      VirtioBusState *bus = VIRTIO_BUS(qbus);
>      VirtioBusClass *klass = VIRTIO_BUS_GET_CLASS(bus);
>      VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
> +    bool has_iommu = virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
>  
>      DPRINTF("%s: plug device.\n", qbus->name);
>  
> @@ -63,8 +64,8 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, Error **errp)
>          klass->device_plugged(qbus->parent, errp);
>      }
>  
> -    if (klass->get_dma_as != NULL &&
> -        virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) {
> +    if (klass->get_dma_as != NULL && has_iommu) {
> +        virtio_add_feature(&vdev->host_features, VIRTIO_F_IOMMU_PLATFORM);
>          vdev->dma_as = klass->get_dma_as(qbus->parent);
>      } else {
>          vdev->dma_as = &address_space_memory;

I suspect that's not enough, we must also fail or disable vhost
(depending on the options), otherwise things won't work.

> -- 
> 2.7.4