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

From: Peter Xu
Subject: Re: [Qemu-devel] [PATCH RFC v3 14/14] intel_iommu: enable vfio devices
Date: Thu, 19 Jan 2017 11:32:56 +0800
User-agent: Mutt/1.5.24 (2015-08-30)

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?


> >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?


-- peterx

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