RE: (proposal) RE: [PATCH v7 00/16] vfio: expose virtual Shared Virtual Addressing to VMs

Liu, Yi L
2020-10-20T14:01:08Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Tuesday, October 20, 2020 9:55 PM
>
> On Tue, Oct 20, 2020 at 09:40:14AM +0000, Liu, Yi L wrote:
>
> > > See previous discussion with Kevin. If I understand correctly, you expect a
> shared
> > > L2 table if vDPA and VFIO device are using the same PASID.
> >
> > L2 table sharing is not mandatory. The mapping is the same, but no need to
> > assume L2 tables are shared. Especially for VFIO/vDPA devices. Even within
> > a passthru framework, like VFIO, if the attributes of backend IOMMU are not
> > the same, the L2 page table are not shared, but the mapping is the same.
>
> I think not being able to share the PASID shows exactly why this VFIO
> centric approach is bad.

no, I didn't say PASID is not sharable. My point is sharing L2 page table is
not mandatory.

Regards,
Yi Liu

> Jason