[PATCH 2/4] mm/gup: explicitly define and check internal GUP flags, disallow FOLL_TOUCH

[Lorenzo Stoakes]

Rather than open-coding a list of internal GUP flags in
is_valid_gup_args(), define which ones are internal.

In addition, we were not explicitly checking to see if the user passed in
FOLL_TOUCH somehow, this patch fixes that.

Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
---
 mm/gup.c      | 5 ++---
 mm/internal.h | 3 +++
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 2f8a2d89fde1..b21b33d1787e 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2227,12 +2227,11 @@ static bool is_valid_gup_args(struct page **pages, int *locked,
 	/*
 	 * These flags not allowed to be specified externally to the gup
 	 * interfaces:
-	 * - FOLL_PIN/FOLL_TRIED/FOLL_FAST_ONLY are internal only
+	 * - FOLL_TOUCH/FOLL_PIN/FOLL_TRIED/FOLL_FAST_ONLY are internal only
 	 * - FOLL_REMOTE is internal only and used on follow_page()
 	 * - FOLL_UNLOCKABLE is internal only and used if locked is !NULL
 	 */
-	if (WARN_ON_ONCE(gup_flags & (FOLL_PIN | FOLL_TRIED | FOLL_UNLOCKABLE |
-				      FOLL_REMOTE | FOLL_FAST_ONLY)))
+	if (WARN_ON_ONCE(gup_flags & INTERNAL_GUP_FLAGS))
 		return false;
 
 	gup_flags |= to_set;
diff --git a/mm/internal.h b/mm/internal.h
index 449891ad7fdb..499016c6b01d 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1018,6 +1018,9 @@ enum {
 	FOLL_UNLOCKABLE = 1 << 21,
 };
 
+#define INTERNAL_GUP_FLAGS (FOLL_TOUCH | FOLL_TRIED | FOLL_REMOTE | FOLL_PIN | \
+			    FOLL_FAST_ONLY | FOLL_UNLOCKABLE)
+
 /*
  * Indicates for which pages that are write-protected in the page table,
  * whether GUP has to trigger unsharing via FAULT_FLAG_UNSHARE such that the
-- 
2.42.0