[PATCH RFC 04/39] mm/rmap: introduce and use hugetlb_try_dup_anon_rmap()

[David Hildenbrand <david@xxxxxxxxxx>]

hugetlb rmap handling differs quite a lot from "ordinary" rmap code.
For example, hugetlb currently only supports entire mappings, and treats
any mapping as mapped using a single "logical PTE". Let's move it out
of the way so we can overhaul our "ordinary" rmap.
implementation/interface.

So let's introduce and use hugetlb_try_dup_anon_rmap() to make all
hugetlb handling use dedicated hugetlb_* rmap functions.

Note that is_device_private_page() does not apply to hugetlb.

Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 include/linux/mm.h   | 12 +++++++++---
 include/linux/rmap.h | 15 +++++++++++++++
 mm/hugetlb.c         |  3 +--
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 418d26608ece7..24c1c7c5a99c0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1953,15 +1953,21 @@ static inline bool page_maybe_dma_pinned(struct page *page)
  *
  * The caller has to hold the PT lock and the vma->vm_mm->->write_protect_seq.
  */
-static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
-					  struct page *page)
+static inline bool folio_needs_cow_for_dma(struct vm_area_struct *vma,
+					  struct folio *folio)
 {
 	VM_BUG_ON(!(raw_read_seqcount(&vma->vm_mm->write_protect_seq) & 1));
 
 	if (!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags))
 		return false;
 
-	return page_maybe_dma_pinned(page);
+	return folio_maybe_dma_pinned(folio);
+}
+
+static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
+					  struct page *page)
+{
+	return folio_needs_cow_for_dma(vma, page_folio(page));
 }
 
 /**
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 0a81e8420a961..8068c332e2ce5 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -208,6 +208,21 @@ void hugetlb_add_anon_rmap(struct folio *, struct vm_area_struct *,
 void hugetlb_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
 		unsigned long address);
 
+/* See page_try_dup_anon_rmap() */
+static inline int hugetlb_try_dup_anon_rmap(struct folio *folio,
+		struct vm_area_struct *vma)
+{
+	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+
+	if (PageAnonExclusive(&folio->page)) {
+		if (unlikely(folio_needs_cow_for_dma(vma, folio)))
+			return -EBUSY;
+		ClearPageAnonExclusive(&folio->page);
+	}
+	atomic_inc(&folio->_entire_mapcount);
+	return 0;
+}
+
 static inline void hugetlb_add_file_rmap(struct folio *folio)
 {
 	VM_WARN_ON_FOLIO(folio_test_anon(folio), folio);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 541a8f38cfdc7..d927f8b2893c0 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5402,8 +5402,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
 			 */
 			if (!folio_test_anon(pte_folio)) {
 				hugetlb_add_file_rmap(pte_folio);
-			} else if (page_try_dup_anon_rmap(&pte_folio->page,
-							  true, src_vma)) {
+			} else if (hugetlb_try_dup_anon_rmap(pte_folio, src_vma)) {
 				pte_t src_pte_old = entry;
 				struct folio *new_folio;
 
-- 
2.41.0