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 <jasow...@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.

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


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