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. Co-developed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx> Signed-off-by: Martin Oliveira <martin.oliveira@xxxxxxxxxxxxx> [1]: https://lkml.kernel.org/r/Yy4Ot5MoOhsgYLTQ@xxxxxxxx --- mm/gup.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 00d0a77112f4..28060e41788d 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2614,11 +2614,6 @@ static bool is_valid_gup_args(struct page **pages, int *locked, if (WARN_ON_ONCE((gup_flags & (FOLL_GET | FOLL_PIN)) && !pages)) return false; - /* We want to allow the pgmap to be hot-unplugged at all times */ - if (WARN_ON_ONCE((gup_flags & FOLL_LONGTERM) && - (gup_flags & FOLL_PCI_P2PDMA))) - return false; - *gup_flags_p = gup_flags; return true; } -- 2.34.1
