On Thu, May 03, 2018 at 10:59:55AM +0800, Tiwei Bie wrote:
> This patch introduces the support for VIRTIO_F_IO_BARRIER.
> When this feature is negotiated, driver will use the barriers
> suitable for hardware devices.
> 
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>

I should have thought of this earlier, but why is a new feature bit
necessary?  If a hardware virtio device is in use, then the device
should already negotiate VIRTIO_F_IOMMU_PLATFORM (i.e. use DMA APIs and
IOMMU callbacks).

Does disabling weak_barriers when VIRTIO_F_IOMMU_PLATFORM is set solve
the problem?