Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

[Jason Gunthorpe]

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.

> > 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