various improvements to the GUP interface

A series of fixes to simplify and improve the GUP interface with an eye to
providing groundwork to future improvements:-

* __access_remote_vm() and access_remote_vm() are functionally identical,
  so make the former static such that in future we can potentially change
  the external-facing implementation details of this function.

* Extend is_valid_gup_args() to cover the missing FOLL_TOUCH case, and
  simplify things by defining INTERNAL_GUP_FLAGS to check against.

* Adjust __get_user_pages_locked() to explicitly treat a failure to pin any
  pages as an error in all circumstances other than FOLL_NOWAIT being
  specified, bringing it in line with the nommu implementation of this
  function.

* (With many thanks to Arnd who suggested this in the first instance)
  Update get_user_page_vma_remote() to explicitly only return a page or an
  error, simplifying the interface and avoiding the questionable
  IS_ERR_OR_NULL() pattern.

Lorenzo Stoakes (4):
  mm: make __access_remote_vm() static
  mm/gup: explicitly define and check internal GUP flags, disallow
    FOLL_TOUCH
  mm/gup: make failure to pin an error if FOLL_NOWAIT not specified
  mm/gup: adapt get_user_page_vma_remote() to never return NULL

 arch/arm64/kernel/mte.c |  4 ++--
 include/linux/mm.h      | 18 +++++++++++++-----
 kernel/events/uprobes.c |  4 ++--
 kernel/ptrace.c         |  2 +-
 mm/gup.c                | 16 +++++++++++++---
 mm/internal.h           |  3 +++
 mm/memory.c             |  7 +++----
 mm/nommu.c              |  4 ++--
 8 files changed, 39 insertions(+), 19 deletions(-)

-- 
2.42.0