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List:       kvm
Subject:    RE: [RFC v2 00/22] intel_iommu: expose Shared Virtual Addressing to VM
From:       "Liu, Yi L" <yi.l.liu () intel ! com>
Date:       2019-10-31 14:07:59
Message-ID: A2975661238FB949B60364EF0F2C25743A0EACA6 () SHSMSX104 ! ccr ! corp ! intel ! com
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> From: Jason Wang [mailto:jasowang@redhat.com]
> 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:jasowang@redhat.com]
> >> 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. :-)

Regards,
Yi Liu
> 
> Thanks
> 
> >


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