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

[Tian, Kevin]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Tuesday, March 30, 2021 9:29 PM
> 
> >
> > 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