Re: [RFC] virtio: Use DMA MAP API for devices without an IOMMU

[Anshuman Khandual]

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.