Revert "mm/gup: reintroduce pin_user_pages_fast_only()"

This reverts commit ef467f3.

This helper is no longer used by the FIPS-mode RNG, which was the
motivation for reintroducing it. Remove it.

Signed-off-by: Sultan Alsawaf <sultan@ciq.com>

Author: kerneltoast

include/linux/mm.h

@@ -2577,8 +2577,6 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 			unsigned int gup_flags, struct page **pages);
 int pin_user_pages_fast(unsigned long start, int nr_pages,
 			unsigned int gup_flags, struct page **pages);
-int pin_user_pages_fast_only(unsigned long start, int nr_pages,
-			     unsigned int gup_flags, struct page **pages);
 void folio_add_pin(struct folio *folio);
 
 int account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc);

mm/gup.c

@@ -3491,20 +3491,6 @@ int pin_user_pages_fast(unsigned long start, int nr_pages,
 }
 EXPORT_SYMBOL_GPL(pin_user_pages_fast);
 
-/*
- * This is the FOLL_PIN equivalent of get_user_pages_fast_only(). Behavior is
- * the same, except that this one sets FOLL_PIN instead of FOLL_GET.
- */
-int pin_user_pages_fast_only(unsigned long start, int nr_pages,
-			     unsigned int gup_flags, struct page **pages)
-{
-	if (!is_valid_gup_args(pages, NULL, &gup_flags,
-			       FOLL_PIN | FOLL_FAST_ONLY))
-		return -EINVAL;
-	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
-}
-EXPORT_SYMBOL_GPL(pin_user_pages_fast_only);
-
 /**
  * pin_user_pages_remote() - pin pages of a remote process
  *