On Thu, Apr 15, 2021 at 03:11:19PM +0200, Auger Eric wrote: > Hi Jason, > > On 4/1/21 6:03 PM, Jason Gunthorpe wrote: > > On Thu, Apr 01, 2021 at 02:08:17PM +0000, Liu, Yi L wrote: > > > >> DMA page faults are delivered to root-complex via page request message and > >> it is per-device according to PCIe spec. Page request handling flow is: > >> > >> 1) iommu driver receives a page request from device > >> 2) iommu driver parses the page request message. Get the RID,PASID, faulted > >> page and requested permissions etc. > >> 3) iommu driver triggers fault handler registered by device driver with > >> iommu_report_device_fault() > > > > This seems confused. > > > > The PASID should define how to handle the page fault, not the driver. > > In my series I don't use PASID at all. I am just enabling nested stage > and the guest uses a single context. I don't allocate any user PASID at > any point. > > When there is a fault at physical level (a stage 1 fault that concerns > the guest), this latter needs to be reported and injected into the > guest. The vfio pci driver registers a fault handler to the iommu layer > and in that fault handler it fills a circ bugger and triggers an eventfd > that is listened to by the VFIO-PCI QEMU device. this latter retrives > the faault from the mmapped circ buffer, it knowns which vIOMMU it is > attached to, and passes the fault to the vIOMMU. > Then the vIOMMU triggers and IRQ in the guest. > > We are reusing the existing concepts from VFIO, region, IRQ to do that. > > For that use case, would you also use /dev/ioasid? /dev/ioasid could do all the things you described vfio-pci as doing, it can even do them the same way you just described. Stated another way, do you plan to duplicate all of this code someday for vfio-cxl? What about for vfio-platform? ARM SMMU can be hooked to platform devices, right? I feel what you guys are struggling with is some choice in the iommu kernel APIs that cause the events to be delivered to the pci_device owner, not the PASID owner. That feels solvable. Jason
