Re: [Qemu-devel] [PATCH RFC v3 14/14] intel_iommu: enable vfio devices

[Jason Wang <jasowang@redhat.com>]

On 2017年01月19日 11:32, Peter Xu wrote:
> On Wed, Jan 18, 2017 at 06:06:57PM +0800, Jason Wang wrote:
>
> [...]
>
>> So I think we should implement DSI and GLOBAL for vfio in this case. We can
>> first try to implement it through current VFIO API which can accepts a range
>> of iova. If not possible, let's discuss for other possible solutions.
> Do you mean VFIO_IOMMU_UNMAP_DMA here?
>
> [...]

Yes.

>
>>> If my understanding above is correct, there is nothing wrong with
>>> above IOMMU driver code - actually it makes sense on bare metal
>>> when CM is disabled.
>>>
>>> But yes, DSI/GLOBAL is far less efficient than PSI when CM is enabled.
>>> We rely on cache invalidations to indirectly capture remapping structure
>>> change. PSI provides accurate info, while DSI/GLOBAL doesn't. To
>>> emulate correct behavior of DSI/GLOBAL, we have to pretend that
>>> the whole address space (iova=0, size=agaw) needs to be unmapped
>>> (for GLOBAL it further means multiple address spaces)
>> Maybe a trick to have accurate info is virtual Device IOTLB.
> Could you elaborate a bit on this?
>
> Thanks,
>
> -- peterx

I think the trick is if guest knows device has device IOTLB, it will 
explicit flush with accurate iova range.

Thanks