On Tue, Apr 06, 2021 at 12:37:35AM +0000, Tian, Kevin wrote:

With nested translation it is GVA->GPA->HPA. The kernel needs to
fix fault related to GPA->HPA (managed by VFIO/VDPA) while 
handle_mm_fault only handles HVA->HPA. In this case, the 2nd-level
page fault is expected to be delivered to VFIO/VDPA first which then
find HVA related to GPA, call handle_mm_fault to fix HVA->HPA,
and then call iommu_map to fix GPA->HPA in the IOMMU page table.
This is exactly like how CPU EPT violation is handled.

No, it should all be in the /dev/ioasid layer not duplicated into
every user.

quoted

If the fault needs to be fixed in the guest, then it needs to be
delivered over /dev/ioasid in some way and injected into the
vIOMMU. VFIO and VDPA have nothing to do with vIOMMU driver in quemu.

You need to have an interface under /dev/ioasid to create both page
table levels and part of that will be to tell the kernel what VA is
mapped and how to handle faults.

VFIO/VDPA already have their own interface to manage GPA->HPA
mappings. Why do we want to duplicate it in /dev/ioasid? 

They have their own interface to manage other types of HW, we should
not duplicate PASID programming into there too.

Jason