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

@@ -2625,8 +2625,6 @@ 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

@@ -3327,34 +3327,6 @@ int pin_user_pages_fast(unsigned long start, int nr_pages,
 }
 EXPORT_SYMBOL_GPL(pin_user_pages_fast);
 
-/**
- * pin_user_pages_fast_only() - pin user pages in memory
- * @start:      starting user address
- * @nr_pages:   number of pages from start to pin
- * @gup_flags:  flags modifying pin behaviour
- * @pages:      array that receives pointers to the pages pinned.
- *              Should be at least nr_pages long.
- *
- * Like pin_user_pages_fast() except it's IRQ-safe in that it won't fall back to
- * the regular GUP.
- *
- * If the architecture does not support this function, simply return with no
- * pages pinned.
- *
- * Careful, careful! COW breaking can go either way, so a non-write
- * access can get ambiguous page results. If you call this function without
- * 'write' set, you'd better be sure that you're ok with that ambiguity.
- */
-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 gup_fast_fallback(start, nr_pages, gup_flags, pages);
-}
-EXPORT_SYMBOL_GPL(pin_user_pages_fast_only);
-
 /**
  * pin_user_pages_remote() - pin pages of a remote process
  *