On Thu, Apr 22, 2021 at 07:02:20PM +0200, Kevin Wolf wrote:
> Commit 2943b53f6 (' virtio: force VIRTIO_F_IOMMU_PLATFORM') made sure
> that vhost can't just reject VIRTIO_F_IOMMU_PLATFORM when it was
> requested. However, just adding it back to the negotiated flags isn't
> right either because it promises support to the guest that the device
> actually doesn't support. One example of a vhost-user device that
> doesn't have support for the flag is the vhost-user-blk export of QEMU.
>
> Instead of successfully creating a device that doesn't work, just fail
> to plug the device when it doesn't support the feature, but it was
> requested. This results in much clearer error messages.
>
> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1935031
> Signed-off-by: Kevin Wolf <kw...@redhat.com>
> ---
> hw/virtio/virtio-bus.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
> index d6332d45c3..859978d248 100644
> --- a/hw/virtio/virtio-bus.c
> +++ b/hw/virtio/virtio-bus.c
> @@ -69,6 +69,11 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, Error
> **errp)
> return;
> }
>
Can you explain this check a little more?
Above we have:
bool has_iommu = virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
and then we get the host features from the bckend:
vdev->host_features = vdc->get_features(vdev, vdev->host_features
So as is this is catching the case where vdev->host_features had
VIRTIO_F_IOMMU_PLATFORM set before (by default?), but doesn't now that
the features have been retrieved?
Why not just:
if (!virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) {
> + if (has_iommu && !virtio_host_has_feature(vdev,
> VIRTIO_F_IOMMU_PLATFORM)) {
> + error_setg(errp, "iommu_platform=true is not supported by the
> device");
> + return;
> + }
> +
> if (klass->device_plugged != NULL) {
> klass->device_plugged(qbus->parent, &local_err);
> }
> --
> 2.30.2
>
