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

[Jason Wang]

On 2019/10/31 下午10:07, Liu, Yi L wrote:
> > From: Jason Wang [mailto:address@hidden]
> > Sent: Thursday, October 31, 2019 5:33 AM
> > Subject: Re: [RFC v2 00/22] intel_iommu: expose Shared Virtual Addressing to VM
> >
> >
> > 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?
> Echo Kevin's reply. We use nested translation here. For stage-1, yes, no need 
> to use
> VFIO DMA API. For stage-2, we still use VFIO DMA API to program the GPA->HPA
> mapping to host. :-)


Cool, two more questions:

- Can EPT shares its page table with IOMMU L2?

- Similar to EPT, when GPA->HPA (actually HVA->HPA) is modified by mm, 
VFIO need to use MMU notifier do modify L2 accordingly besides DMA API?

Thanks


> Regards,
> Yi Liu
> > Thanks