From: Jason Gunthorpe <redacted>
Sent: Tuesday, March 30, 2021 9:29 PM

quoted

First, userspace may use ioasid in a non-SVA scenario where ioasid is
bound to specific security context (e.g. a control vq in vDPA) instead of
tying to mm. In this case there is no pgtable binding initiated from user
space. Instead, ioasid is allocated from /dev/ioasid and then programmed
to the intended security context through specific passthrough framework
which manages that context.

This sounds like the exact opposite of what I'd like to see.

I do not want to see every subsystem gaining APIs to program a
PASID. All of that should be consolidated in *one place*.

I do not want to see VDPA and VFIO have two nearly identical sets of
APIs to control the PASID.

Drivers consuming a PASID, like VDPA, should consume the PASID and do
nothing more than authorize the HW to use it.

quemu should have general code under the viommu driver that drives
/dev/ioasid to create PASID's and manage the IO mapping according to
the guest's needs.

Drivers like VDPA and VFIO should simply accept that PASID and
configure/authorize their HW to do DMA's with its tag.

I agree with you on consolidating things in one place (especially for the
general SVA support). But here I was referring to an usage without 
pgtable binding (Possibly Jason. W can say more here), where the 
userspace just wants to allocate PASIDs, program/accept PASIDs to 
various workqueues (device specific), and then use MAP/UNMAP 
interface to manage address spaces associated with each PASID. 
I just wanted to point out that the latter two steps are through 
VFIO/VDPA specific interfaces. 

Thanks
Kevin