[PATCH v2 3/4] mm: internal: introduce FPB_LOCKLESS for folio_pte_batch_flags()

[Yeoreum Yun <yeoreum.yun@arm.com>]

From: Yuan-Hao Hsu <aa9736195201@gmail.com>

Add support for calling folio_pte_batch_flags() in GUP-fast context when we are
not holding the PT lock. Instead of reading PTEs through ptep_get(), we have to
use ptep_get_lockless().

Specify the new behavior through a new flag FPB_LOCKLESS. We'll make use of this
functionality for batching PTEs in gup_fast_pte_range() next.

Signed-off-by: Yuan-Hao Hsu <aa9736195201@gmail.com>
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
 mm/internal.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/internal.h b/mm/internal.h
index b4d0df4c35adf..c1824b0193f4d 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -373,6 +373,12 @@ typedef int __bitwise fpb_t;
  */
 #define FPB_MERGE_YOUNG_DIRTY		((__force fpb_t)BIT(4))
 
+/*
+ * Read the page table entries with ptep_get_lockless(): the caller does not
+ * hold the page table lock (e.g, GUP-fast).
+ */
+#define FPB_LOCKLESS			((__force fpb_t)BIT(5))
+
 static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
 {
 	if (!(flags & FPB_RESPECT_DIRTY))
@@ -442,7 +448,7 @@ static inline unsigned int folio_pte_batch_flags(struct folio *folio,
 	ptep = ptep + nr;
 
 	while (nr < max_nr) {
-		pte = ptep_get(ptep);
+		pte = (flags & FPB_LOCKLESS) ? ptep_get_lockless(ptep) : ptep_get(ptep);
 
 		if (!pte_same(__pte_batch_clear_ignored(pte, flags), expected_pte))
 			break;

-- 
2.43.0