| Message ID | 20191204213603.464373-2-jhubbard@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | IB/umem: use get_user_pages_fast() to pin DMA pages | expand |
On Wed, Dec 04, 2019 at 01:36:02PM -0800, 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> > Signed-off-by: John Hubbard <jhubbard@nvidia.com> > --- > mm/gup.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > Thanks, Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
On 12/9/19 10:25 AM, Leon Romanovsky wrote: > On Wed, Dec 04, 2019 at 01:36:02PM -0800, 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> >> Signed-off-by: John Hubbard <jhubbard@nvidia.com> >> --- >> mm/gup.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> > > Thanks, > Reviewed-by: Leon Romanovsky <leonro@mellanox.com> > Hi Leon, thanks for the reviews, great timing! I'll add the tags to the commits, which I'm just about to post as part of the larger "pin user pages" patchset. thanks,
diff --git a/mm/gup.c b/mm/gup.c index 7646bf993b25..5244b8090440 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2415,7 +2415,8 @@ 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> Signed-off-by: John Hubbard <jhubbard@nvidia.com> --- mm/gup.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)