[PATCH v4 2/3] gup: introduce unpin_user_folio_dirty_locked()

[lizhe.67@bytedance.com]

From: Li Zhe <lizhe.67@bytedance.com>

Introduce a new interface, unpin_user_folio_dirty_locked(). This
interface is similar to unpin_user_folio(), but it adds the
capability to conditionally mark a folio as dirty. VFIO will utilize
this interface to accelerate the VFIO DMA unmap process.

Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
---
 include/linux/mm.h |  2 ++
 mm/gup.c           | 27 +++++++++++++++++++++------
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index fdda6b16263b..242b05671502 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1689,6 +1689,8 @@ void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
 				      bool make_dirty);
 void unpin_user_pages(struct page **pages, unsigned long npages);
 void unpin_user_folio(struct folio *folio, unsigned long npages);
+void unpin_user_folio_dirty_locked(struct folio *folio,
+		unsigned long npins, bool make_dirty);
 void unpin_folios(struct folio **folios, unsigned long nfolios);
 
 static inline bool is_cow_mapping(vm_flags_t flags)
diff --git a/mm/gup.c b/mm/gup.c
index 84461d384ae2..15debead5f5b 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -360,12 +360,7 @@ void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
 
 	for (i = 0; i < npages; i += nr) {
 		folio = gup_folio_range_next(page, npages, i, &nr);
-		if (make_dirty && !folio_test_dirty(folio)) {
-			folio_lock(folio);
-			folio_mark_dirty(folio);
-			folio_unlock(folio);
-		}
-		gup_put_folio(folio, nr, FOLL_PIN);
+		unpin_user_folio_dirty_locked(folio, nr, make_dirty);
 	}
 }
 EXPORT_SYMBOL(unpin_user_page_range_dirty_lock);
@@ -435,6 +430,26 @@ void unpin_user_folio(struct folio *folio, unsigned long npages)
 }
 EXPORT_SYMBOL(unpin_user_folio);
 
+/**
+ * unpin_user_folio_dirty_locked() - conditionally mark a folio
+ * dirty and unpin it
+ *
+ * @folio:  pointer to folio to be released
+ * @npins:  number of pins
+ * @make_dirty: whether to mark the folio dirty
+ *
+ * Mark the folio as being modified if @make_dirty is true. Then
+ * release npins of the folio.
+ */
+void unpin_user_folio_dirty_locked(struct folio *folio,
+		unsigned long npins, bool make_dirty)
+{
+	if (make_dirty && !folio_test_dirty(folio))
+		folio_mark_dirty_lock(folio);
+	gup_put_folio(folio, npins, FOLL_PIN);
+}
+EXPORT_SYMBOL_GPL(unpin_user_folio_dirty_locked);
+
 /**
  * unpin_folios() - release an array of gup-pinned folios.
  * @folios:  array of folios to be marked dirty and released.
-- 
2.20.1