On 2016年12月02日 14:52, Peter Xu wrote: > On Thu, Dec 01, 2016 at 02:44:14PM +0800, Lan Tianyu wrote: > > [...] > >> Hi: >> I think there are still other gaps to enable passthough device with >> vIOMMU's DMA translation support. >> >> 1. Since this patchset is to shadow guest IO page table to >> pIOMMU(physical IOMMU) vfio_dma_map/umap(), there will be some fault >> events from pIOMMU if guest os does misconfigurations. We should report >> these fault events to guest. This means we need to pass the fault event >> from pIOMMU driver to vIOMMU in Qemu. I suppose a channel in VFIO should >> be added to connect pIOMMU and vIOMMU. > > Thanks for raising this up - IMHO this is a good question. > >> >> The task should be divided into three parts >> 1) pIOMMU driver reports fault events for vIOMMU via new VFIO interface > > Here you mean "how host kernel capture the DMAR fault", right?
Yes, VFIO kernel driver should know the fault event when it's triggered. > > IMHO We can have something like notifier/notifiee as well in DMAR > fault reporting - people (like vfio driver in kernel) can register to > fault reports related to specific device. When DMAR receives faults > for those devices, it triggers the notification list, then vfio can be > notified. Yes, something likes this. > >> 2) Add new channel in VFIO subsystem to connect pIOMMU driver and >> vIOMMU in Qemu >> 3) vIOMMU in Qemu get fault event from VFIO subsystem in Qemu and inject >> virtual fault event to guest. >> >> Such VFIO channel is also required by device's PRS(Page Request >> Services) support. This is also a part of SVM(Shared virtual memory) >> support in VM. Here is SVM design doc link. >> http://marc.info/?l=kvm&m=148049586514120&w=2 >> >> 2. How to restore GPA->HPA mapping when IOVA is disabled by guest. >> When guest enables IOVA for device, vIOMMU will invalidate all previous >> GPA->HPA mapping and update IOVA->HPA mapping to pIOMMU via iommu >> notifier. But if IOVA is disabled, I think we should restore GPA->HPA >> mapping for the device otherwise the device won't work again in the VM. > > If we can have a workable replay mechanism, this problem will be > solved IMHO. Basic idea is to replay related memory regions to restore GPA->HPA mapping when guest disables IOVA. -- Best regards Tianyu Lan
