Export a function that adds pins to an already-pinned huge-page folio.
This allows any range of small pages within the folio to be unpinned later.
For example, pages pinned via memfd_pin_folios and modified by
folio_add_pins could be unpinned via unpin_user_page(s).
Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
---
include/linux/mm.h | 1 +
mm/gup.c | 24 ++++++++++++++++++++++++
2 files changed, 25 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 13bff7c..70d5293 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2521,6 +2521,7 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
struct folio **folios, unsigned int max_folios,
pgoff_t *offset);
+int folio_add_pins(struct folio *folio, unsigned int pins);
int get_user_pages_fast(unsigned long start, int nr_pages,
unsigned int gup_flags, struct page **pages);
diff --git a/mm/gup.c b/mm/gup.c
index fcd602b..11c5f27 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -3733,3 +3733,27 @@ long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
return ret;
}
EXPORT_SYMBOL_GPL(memfd_pin_folios);
+
+/**
+ * folio_add_pins() - add pins to an already-pinned folio
+ * @folio: the folio to add more pins to
+ * @pins: number of pins to add
+ *
+ * Try to add more pins to an already-pinned folio. The semantics
+ * of the pin (e.g., FOLL_WRITE) follow any existing pin and cannot
+ * be changed.
+ *
+ * This function is helpful when having obtained a pin on a large folio
+ * using memfd_pin_folios(), but wanting to logically unpin parts
+ * (e.g., individual pages) of the folio later, for example, using
+ * unpin_user_page_range_dirty_lock().
+ *
+ * This is not the right interface to initially pin a folio.
+ */
+int folio_add_pins(struct folio *folio, unsigned int pins)
+{
+ VM_WARN_ON_ONCE(!folio_maybe_dma_pinned(folio));
+
+ return try_grab_folio(folio, pins, FOLL_PIN);
+}
+EXPORT_SYMBOL_GPL(folio_add_pins);
