On Thu, Aug 08, 2024 at 12:33:39PM -0600, Martin Oliveira wrote: > This check existed originally due to concerns that P2PDMA needed to copy > fsdax until pgmap refcounts were fixed (see [1]). > > The P2PDMA infrastructure will only call unmap_mapping_range() when the > underlying device is unbound, and immediately after unmapping it waits > for the reference of all ZONE_DEVICE pages to be released before > continuing. This does not allow for a page to be reused and no user > access fault is therefore possible. It does not have the same problem as > fsdax. > > The one minor concern with FOLL_LONGTERM pins is they will block device > unbind until userspace releases them all. This is unfortunately not really minor unless we have a well documented way to force this :(
