On Wed, Aug 19, 2020 at 11:01:00PM +1200, Barry Song wrote: > gug prohibits users from calling get_user_pages() with FOLL_PIN. But it > allows users to call get_user_pages() with FOLL_LONGTERM only. It seems > insensible. > > since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit > users from calling get_user_pages() with FOLL_LONGTERM while not with > FOLL_PIN. > > mm/gup_benchmark.c used to be the only user who did this improperly. > But it has been fixed by moving to use pin_user_pages(). > > Cc: John Hubbard <[email protected]> > Cc: Jan Kara <[email protected]> > Cc: Jérôme Glisse <[email protected]> > Cc: "Matthew Wilcox (Oracle)" <[email protected]> > Cc: Al Viro <[email protected]> > Cc: Christoph Hellwig <[email protected]> > Cc: Dan Williams <[email protected]> > Cc: Dave Chinner <[email protected]> > Cc: Jason Gunthorpe <[email protected]> > Cc: Jonathan Corbet <[email protected]> > Cc: Michal Hocko <[email protected]> > Cc: Mike Kravetz <[email protected]> > Cc: Shuah Khan <[email protected]> > Cc: Vlastimil Babka <[email protected]> > Signed-off-by: Barry Song <[email protected]>
Seems reasonable to me. Reviewed-by: Ira Weiny <[email protected]> > --- > mm/gup.c | 37 ++++++++++++++++++++++--------------- > 1 file changed, 22 insertions(+), 15 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index ae096ea7583f..4da669f79566 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1789,6 +1789,25 @@ static long __get_user_pages_remote(struct mm_struct > *mm, > gup_flags | FOLL_TOUCH | FOLL_REMOTE); > } > > +static bool is_valid_gup_flags(unsigned int gup_flags) > +{ > + /* > + * FOLL_PIN must only be set internally by the pin_user_pages*() APIs, > + * never directly by the caller, so enforce that with an assertion: > + */ > + if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > + return false; > + /* > + * FOLL_PIN is a prerequisite to FOLL_LONGTERM. Another way of saying > + * that is, FOLL_LONGTERM is a specific case, more restrictive case of > + * FOLL_PIN. > + */ > + if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM)) > + return false; > + > + return true; > +} > + > /** > * get_user_pages_remote() - pin user pages in memory > * @mm: mm_struct of target mm > @@ -1854,11 +1873,7 @@ long get_user_pages_remote(struct mm_struct *mm, > unsigned int gup_flags, struct page **pages, > struct vm_area_struct **vmas, int *locked) > { > - /* > - * FOLL_PIN must only be set internally by the pin_user_pages*() APIs, > - * never directly by the caller, so enforce that with an assertion: > - */ > - if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > + if (!is_valid_gup_flags(gup_flags)) > return -EINVAL; > > return __get_user_pages_remote(mm, start, nr_pages, gup_flags, > @@ -1904,11 +1919,7 @@ long get_user_pages(unsigned long start, unsigned long > nr_pages, > unsigned int gup_flags, struct page **pages, > struct vm_area_struct **vmas) > { > - /* > - * FOLL_PIN must only be set internally by the pin_user_pages*() APIs, > - * never directly by the caller, so enforce that with an assertion: > - */ > - if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > + if (!is_valid_gup_flags(gup_flags)) > return -EINVAL; > > return __gup_longterm_locked(current->mm, start, nr_pages, > @@ -2810,11 +2821,7 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast_only); > int get_user_pages_fast(unsigned long start, int nr_pages, > unsigned int gup_flags, struct page **pages) > { > - /* > - * FOLL_PIN must only be set internally by the pin_user_pages*() APIs, > - * never directly by the caller, so enforce that: > - */ > - if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > + if (!is_valid_gup_flags(gup_flags)) > return -EINVAL; > > /* > -- > 2.27.0 > > >
