Re: [PATCH v8 08/26] mm/gup: allow FOLL_FORCE for get_user_pages_fast()
From: Jan Kara <jack@suse.cz>
Date: 2019-12-10 10:28:33
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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 <redacted>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>Looks good to me. You can add: Reviewed-by: Jan Kara <jack@suse.cz> Honza
quoted hunk ↗ jump to hunk
--- 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
-- Jan Kara [off-list ref] SUSE Labs, CR