RE: [PATCH 09/10] kvm/vfio: Remove vfio_group from kvm

Tian, Kevin
2022-04-18T06:09:44Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Saturday, April 16, 2022 9:34 AM
>
> On Sat, Apr 16, 2022 at 12:42:50AM +0000, Tian, Kevin wrote:
>
> > Then what about PPC? w/o holding a reference to container is there
> > any impact on spapr_tce_table which is attached to the group?
> > I don't know the relationship between this table and vfio container
> > and whether there is a lifetime dependency in between.
>
> table seems to have its own FD so it should be refcounted
> independently and not indirectly rely on the vfio container. It seemed
> like there was enough protection there..
>

the table in PPC context refers to a window in the global iova address
space. From this angle the reference should be torn down when the
group is detached from the container which represents the address
space. But given the detach operation also prevents the user from
accessing the device, having the reference held by KVM for a while
until KVM_DEV_VFIO_GROUP_DEL is called is probably not harmful.

In any case this is also worth an explanation similar to what you
did for cache coherency.

Thanks
Kevin