[PATCH v8 17/20] mm/gup: Don't allow FOLL_LONGTERM pinning of FS DAX pages

Alistair Popple
2025-02-18T03:57:28Z

Longterm pinning of FS DAX pages should already be disallowed by
various pXX_devmap checks. However a future change will cause these
checks to be invalid for FS DAX pages so make
folio_is_longterm_pinnable() return false for FS DAX pages.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: David Hildenbrand <david@redhat.com>
---
include/linux/memremap.h | 11 +++++++++++
include/linux/mm.h | 7 +++++++
2 files changed, 18 insertions(+)

diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 0256a42..4aa1519 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -187,6 +187,17 @@ static inline bool folio_is_device_coherent(const struct folio *folio)
return is_device_coherent_page(&folio->page);
}

+static inline bool is_fsdax_page(const struct page *page)
+{
+ return is_zone_device_page(page) &&
+ page_pgmap(page)->type == MEMORY_DEVICE_FS_DAX;
+}
+
+static inline bool folio_is_fsdax(const struct folio *folio)
+{
+ return is_fsdax_page(&folio->page);
+}
+
#ifdef CONFIG_ZONE_DEVICE
void zone_device_page_init(struct page *page);
void *memremap_pages(struct dev_pagemap *pgmap, int nid);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index d1f260d..066aebd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2109,6 +2109,13 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
if (folio_is_device_coherent(folio))
return false;

+ /*
+ * Filesystems can only tolerate transient delays to truncate and
+ * hole-punch operations
+ */
+ if (folio_is_fsdax(folio))
+ return false;
+
/* Otherwise, non-movable zone folios can be pinned. */
return !folio_is_zone_movable(folio);

--
git-series 0.9.1