> From: Jason Wang [mailto:jasowang@xxxxxxxxxx] > Sent: Friday, November 1, 2019 3:30 PM > > > On 2019/10/31 下午10:07, Liu, Yi L wrote: > >> From: Jason Wang [mailto:jasowang@xxxxxxxxxx] > >> 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@xxxxxxxxxx] > >>>> 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? yes, their formats are compatible. > > - 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? > VFIO devices need to pin-down guest memory pages that are mapped in IOMMU. So notifier is not required since mm won't change the mapping for those pages. Thanks Kevin
