From: John Hubbard <jhubbard@xxxxxxxxxx> Subject: mm/gup: require FOLL_GET for get_user_pages_fast() Internal to mm/gup.c, require that get_user_pages_fast() and __get_user_pages_fast() identify themselves, by setting FOLL_GET. This is required in order to be able to make decisions based on "FOLL_PIN, or FOLL_GET, or both or neither are set", in upcoming patches. Link: http://lkml.kernel.org/r/20200211001536.1027652-6-jhubbard@xxxxxxxxxx Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> Cc: Ira Weiny <ira.weiny@xxxxxxxxx> Cc: Jérôme Glisse <jglisse@xxxxxxxxxx> Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Dave Chinner <david@xxxxxxxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Shuah Khan <shuah@xxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/gup.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) --- a/mm/gup.c~mm-gup-require-foll_get-for-get_user_pages_fast +++ a/mm/gup.c @@ -2390,6 +2390,14 @@ int __get_user_pages_fast(unsigned long unsigned long len, end; unsigned long flags; int nr = 0; + /* + * Internally (within mm/gup.c), gup fast variants must set FOLL_GET, + * because gup fast is always a "pin with a +1 page refcount" request. + */ + unsigned int gup_flags = FOLL_GET; + + if (write) + gup_flags |= FOLL_WRITE; start = untagged_addr(start) & PAGE_MASK; len = (unsigned long) nr_pages << PAGE_SHIFT; @@ -2415,7 +2423,7 @@ int __get_user_pages_fast(unsigned long if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && gup_fast_permitted(start, end)) { local_irq_save(flags); - gup_pgd_range(start, end, write ? FOLL_WRITE : 0, pages, &nr); + gup_pgd_range(start, end, gup_flags, pages, &nr); local_irq_restore(flags); } @@ -2454,7 +2462,7 @@ static int internal_get_user_pages_fast( int nr = 0, ret = 0; if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | - FOLL_FORCE | FOLL_PIN))) + FOLL_FORCE | FOLL_PIN | FOLL_GET))) return -EINVAL; start = untagged_addr(start) & PAGE_MASK; @@ -2521,6 +2529,13 @@ int get_user_pages_fast(unsigned long st if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) return -EINVAL; + /* + * The caller may or may not have explicitly set FOLL_GET; either way is + * OK. However, internally (within mm/gup.c), gup fast variants must set + * FOLL_GET, because gup fast is always a "pin with a +1 page refcount" + * request. + */ + gup_flags |= FOLL_GET; return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); } EXPORT_SYMBOL_GPL(get_user_pages_fast); _
