On 04/06/2018 02:48 AM, Benjamin Herrenschmidt wrote: > On Thu, 2018-04-05 at 21:34 +0300, Michael S. Tsirkin wrote: >>> In this specific case, because that would make qemu expect an iommu, >>> and there isn't one. >> >> >> I think that you can set iommu_platform in qemu without an iommu. > > No I mean the platform has one but it's not desirable for it to be used > due to the performance hit.
Also the only requirement is to bounce the I/O buffers through SWIOTLB implemented as DMA API which the virtio core understands. There is no need for an IOMMU to be involved for the device representation in this case IMHO.
