On 02/04/2016 12:16 PM, Tian, Kevin wrote: >>>>> 5) Pin/unpin guest memory >>>>> -- >>>>> IGD or any PCI passthru should have same requirement. So we should be >>>>> able to leverage existing code in VFIO. The only tricky thing (Jike may >>>>> elaborate after he is back), is that KVMGT requires to pin EPT entry too, >>>>> which requires some further change in KVM side. But I'm not sure whether >>>>> it still holds true after some design changes made in this thread. So I'll >>>>> leave to Jike to further comment. >>>> >>>> PCI assignment requires pinning all of guest memory, I would think that >>>> IGD would only need to pin selective memory, so is this simply stating >>>> that both have the need to pin memory, not that they'll do it to the >>>> same extent? >>> >>> For simplicity let's first pin all memory, while taking selective pinning as a >>> future enhancement. >>> >>> The tricky thing is that existing 'pin' action in VFIO doesn't actually pin >>> EPT entry too (only pin host page tables for Qemu process). There are >>> various places where EPT entries might be invalidated when guest is >>> running, while KVMGT requires EPT entries to be pinned too. Let's wait >>> for Jike to elaborate whether this part is still required today. >> >> Sorry, don't quite follow the logic here. The current VFIO TYPE1 IOMMU (including API >> and underlying IOMMU implementation) will pin the guest physical memory and >> install those pages to the proper device domain. Yes, it is only for the QEMU >> process as that is what the VM is running at. >> >> Do I miss something here? > > For Qemu there are two page tables involved: one is host page table as > you mentioned here for root mode, the other is EPT page table used > as the 2nd level translation when guest is running in non-root mode. I'm > not sure why KVMGT requires to pin EPT entry. Jike should know better > here. > There may be some misunderstanding here - KVMGT doesn't need to pin EPT entries. Previously I mentioned spte pinning, only because that, at that time we wanted to query pfn for a given gfn by KVM MMU (rmap + spte). Now we have better way of this. I promise this is not a problem :) -- Thanks, Jike -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
