Re: [Intel-gfx] [PATCH v9 16/25] iommufd/device: Add iommufd_access_detach() API

["Liu, Yi L" <yi.l.liu@intel.com>]

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, April 5, 2023 7:56 PM
> 
> On Tue, Apr 04, 2023 at 04:45:12PM -0600, Alex Williamson wrote:
> > On Sat,  1 Apr 2023 08:18:24 -0700
> > Yi Liu <yi.l.liu@intel.com> wrote:
> >
> > > From: Nicolin Chen <nicolinc@nvidia.com>
> > >
> > > Previously, the detach routine is only done by the destroy(). And it was
> > > called by vfio_iommufd_emulated_unbind() when the device runs close(), so
> > > all the mappings in iopt were cleaned in that setup, when the call trace
> > > reaches this detach() routine.
> > >
> > > Now, there's a need of a detach uAPI, meaning that it does not only need
> > > a new iommufd_access_detach() API, but also requires access->ops->unmap()
> > > call as a cleanup. So add one.
> > >
> > > However, leaving that unprotected can introduce some potential of a race
> > > condition during the pin_/unpin_pages() call, where access->ioas->iopt is
> > > getting referenced. So, add an ioas_lock to protect the context of iopt
> > > referencings.
> > >
> > > Also, to allow the iommufd_access_unpin_pages() callback to happen via
> > > this unmap() call, add an ioas_unpin pointer, so the unpin routine won't
> > > be affected by the "access->ioas = NULL" trick.
> > >
> > > Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> > > Tested-by: Terrence Xu <terrence.xu@intel.com>
> > > Tested-by: Yanting Jiang <yanting.jiang@intel.com>
> > > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> > > Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> > > ---
> > >  drivers/iommu/iommufd/device.c          | 76 +++++++++++++++++++++++--
> > >  drivers/iommu/iommufd/iommufd_private.h |  2 +
> > >  include/linux/iommufd.h                 |  1 +
> > >  3 files changed, 74 insertions(+), 5 deletions(-)
> >
> > Does this need to go in via iommufd first?  There seems to be quite a
> > bit of churn in iommufd/device.c vs the vfio_mdev_ops branch (ie. it
> > doesn't apply). Thanks,
> 
> I think it is best to stay with this series, Yi has to rebase it

The rebased version is here. Shall I resend a version which is rebased on
top of vfio_mdev_ops?

https://github.com/yiliu1765/iommufd/commit/d3d8f65c82fe2ca2a7b1a635f4b40b2a0971daa9

Regards,
Yi Liu