RE: [PATCH v4 3/5] iommufd: Add replace support in iommufd_access_set_ioas()

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Sent: Wednesday, March 8, 2023 10:26 PM
> 
> Support an access->ioas replacement in iommufd_access_set_ioas(), which
> sets the access->ioas to NULL provisionally so that any further incoming
> iommufd_access_pin_pages() callback can be blocked.
> 
> Then, call access->ops->unmap() to clean up the entire iopt. To allow an
> 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 above.
> 
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>