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

[Jason Wang]

On 2017年01月17日 22:44, Michael S. Tsirkin wrote:
> 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 <address@hidden>
> > ---
> >   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.

Looks like with the patch, VIRTIO_F_IOMMU_PLATFORM will be passed to 
vhost_set_features(). So if vhost backend does not support it, it will 
fall back to userspace (This may not work for vhost-user, but it's a bug 
existed even before this patch).

Thanks