mm/gup: explicitly define and check internal GUP flags, disallow FOLL_TOUCH

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

In addition, explicitly check to see if the user passed in FOLL_TOUCH
somehow, as this appears to have been accidentally excluded.

Link: https://lkml.kernel.org/r/971e013dfe20915612ea8b704e801d7aef9a66b6.1696288092.git.lstoakes@gmail.comSigned-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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;

mm/internal.h

@@ -1017,6 +1017,9 @@ 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