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Message-ID: <CAFqt6zb2GjO9KOVdKT1P0P-Wn+isnArous5gpw-AJ3va+fi9rw@mail.gmail.com>
Date: Thu, 3 Sep 2020 12:42:44 +0530
From: Souptick Joarder <jrdr.linux@...il.com>
To: John Hubbard <jhubbard@...dia.com>
Cc: Barry Song <song.bao.hua@...ilicon.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org,
linuxarm@...wei.com, Jan Kara <jack@...e.cz>,
Jérôme Glisse <jglisse@...hat.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Al Viro <viro@...iv.linux.org.uk>,
Christoph Hellwig <hch@...radead.org>,
Dan Williams <dan.j.williams@...el.com>,
Dave Chinner <david@...morbit.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Jonathan Corbet <corbet@....net>,
Michal Hocko <mhocko@...e.com>,
Mike Kravetz <mike.kravetz@...cle.com>,
Shuah Khan <shuah@...nel.org>, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM
On Wed, Aug 19, 2020 at 11:45 PM John Hubbard <jhubbard@...dia.com> wrote:
>
> On 8/19/20 4:01 AM, Barry Song wrote:
> > gug prohibits users from calling get_user_pages() with FOLL_PIN. But it
>
> Maybe Andrew can fix the typo above: gug --> gup.
>
>
> > 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().
>
> For future patches, you don't have to write everything in the
> commit log. Some things are better placed in a cover letter or after
> the "---" line, because they don't need to be recorded forever.
>
> Anyway, the diffs seem fine, assuming that you've audited the call sites.
We can use is_valid_gup_flags() inside ->
get_user_pages_locked(),
get_user_pages_unlocked(),
pin_user_pages_locked() as well.
Are you planning to add it in future patches ?
>
> thanks,
> --
> John Hubbard
> NVIDIA
>
> >
> > Cc: John Hubbard <jhubbard@...dia.com>
> > Cc: Jan Kara <jack@...e.cz>
> > Cc: Jérôme Glisse <jglisse@...hat.com>
> > Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > Cc: Christoph Hellwig <hch@...radead.org>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > Cc: Dave Chinner <david@...morbit.com>
> > Cc: Jason Gunthorpe <jgg@...pe.ca>
> > Cc: Jonathan Corbet <corbet@....net>
> > Cc: Michal Hocko <mhocko@...e.com>
> > Cc: Mike Kravetz <mike.kravetz@...cle.com>
> > Cc: Shuah Khan <shuah@...nel.org>
> > Cc: Vlastimil Babka <vbabka@...e.cz>
> > Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
> > ---
> > 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;
> >
> > /*
> >
>
>
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