| Message ID | 20191209225344.99740-9-jhubbard@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/gup: track dma-pinned pages: FOLL_PIN | expand |
On Mon 09-12-19 14:53:26, John Hubbard wrote: > Commit 817be129e6f2 ("mm: validate get_user_pages_fast flags") allowed > only FOLL_WRITE and FOLL_LONGTERM to be passed to get_user_pages_fast(). > This, combined with the fact that get_user_pages_fast() falls back to > "slow gup", which *does* accept FOLL_FORCE, leads to an odd situation: > if you need FOLL_FORCE, you cannot call get_user_pages_fast(). > > There does not appear to be any reason for filtering out FOLL_FORCE. > There is nothing in the _fast() implementation that requires that we > avoid writing to the pages. So it appears to have been an oversight. > > Fix by allowing FOLL_FORCE to be set for get_user_pages_fast(). > > Fixes: 817be129e6f2 ("mm: validate get_user_pages_fast flags") > Cc: Christoph Hellwig <hch@lst.de> > Reviewed-by: Leon Romanovsky <leonro@mellanox.com> > Signed-off-by: John Hubbard <jhubbard@nvidia.com> Looks good to me. You can add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > mm/gup.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/gup.c b/mm/gup.c > index c0c56888e7cc..958ab0757389 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2414,7 +2414,8 @@ int get_user_pages_fast(unsigned long start, int nr_pages, > unsigned long addr, len, end; > int nr = 0, ret = 0; > > - if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM))) > + if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | > + FOLL_FORCE))) > return -EINVAL; > > start = untagged_addr(start) & PAGE_MASK; > -- > 2.24.0 >
diff --git a/mm/gup.c b/mm/gup.c index c0c56888e7cc..958ab0757389 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2414,7 +2414,8 @@ int get_user_pages_fast(unsigned long start, int nr_pages, unsigned long addr, len, end; int nr = 0, ret = 0; - if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM))) + if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | + FOLL_FORCE))) return -EINVAL; start = untagged_addr(start) & PAGE_MASK;
Commit 817be129e6f2 ("mm: validate get_user_pages_fast flags") allowed only FOLL_WRITE and FOLL_LONGTERM to be passed to get_user_pages_fast(). This, combined with the fact that get_user_pages_fast() falls back to "slow gup", which *does* accept FOLL_FORCE, leads to an odd situation: if you need FOLL_FORCE, you cannot call get_user_pages_fast(). There does not appear to be any reason for filtering out FOLL_FORCE. There is nothing in the _fast() implementation that requires that we avoid writing to the pages. So it appears to have been an oversight. Fix by allowing FOLL_FORCE to be set for get_user_pages_fast(). Fixes: 817be129e6f2 ("mm: validate get_user_pages_fast flags") Cc: Christoph Hellwig <hch@lst.de> Reviewed-by: Leon Romanovsky <leonro@mellanox.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> --- mm/gup.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)