RE: [RFC v2 00/22] intel_iommu: expose Shared Virtual Addressing to VM

[Tian, Kevin]

> From: Jason Wang [mailto:address@hidden]
> Sent: Thursday, October 31, 2019 12:33 PM
> 
> 
> On 2019/10/25 下午6:12, Tian, Kevin wrote:
> >> From: Jason Wang [mailto:address@hidden]
> >> Sent: Friday, October 25, 2019 5:49 PM
> >>
> >>
> >> On 2019/10/24 下午8:34, Liu Yi L wrote:
> >>> Shared virtual address (SVA), a.k.a, Shared virtual memory (SVM) on
> Intel
> >>> platforms allow address space sharing between device DMA and
> >> applications.
> >>
> >>
> >> Interesting, so the below figure demonstrates the case of VM. I wonder
> >> how much differences if we compare it with doing SVM between device
> >> and
> >> an ordinary process (e.g dpdk)?
> >>
> >> Thanks
> > One difference is that ordinary process requires only stage-1 translation,
> > while VM requires nested translation.
> 
> 
> A silly question, then I believe there's no need for VFIO DMA API in
> this case consider the page table is shared between MMU and IOMMU?
> 

yes, only need to intercept guest iotlb invalidation request on stage-1 
translation and then forward to IOMMU through new VFIO API. Existing
VFIO DMA API applies to only the stage-2 translation (GPA->HPA) here.

Thanks
Kevin