[PATCHv3 1/6] mm/page_vma_mapped: Track if the page is mapped across page table boundary

[Kiryl Shutsemau <kirill@shutemov.name>]

From: Kiryl Shutsemau <kas@kernel.org>

Add a PVMW_PGTABLE_CROSSSED flag that page_vma_mapped_walk() will set if
the page is mapped across page table boundary. Unlike other PVMW_*
flags, this one is result of page_vma_mapped_walk() and not set by the
caller.

folio_referenced_one() will use it to detect if it safe to mlock the
folio.

Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
---
 include/linux/rmap.h | 5 +++++
 mm/page_vma_mapped.c | 1 +
 2 files changed, 6 insertions(+)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 6cd020eea37a..4f4659c0fc93 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -928,6 +928,11 @@ struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr,
 /* Look for migration entries rather than present PTEs */
 #define PVMW_MIGRATION		(1 << 1)
 
+/* Result flags */
+
+/* The page is mapped across page table boundary */
+#define PVMW_PGTABLE_CROSSSED	(1 << 16)
+
 struct page_vma_mapped_walk {
 	unsigned long pfn;
 	unsigned long nr_pages;
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index e981a1a292d2..a184b88743c3 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -309,6 +309,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 				}
 				pte_unmap(pvmw->pte);
 				pvmw->pte = NULL;
+				pvmw->flags |= PVMW_PGTABLE_CROSSSED;
 				goto restart;
 			}
 			pvmw->pte++;
-- 
2.50.1