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Subject[PATCH v2 1/2] mm/gup: allow FOLL_FORCE for get_user_pages_fast()
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 <>
Signed-off-by: John Hubbard <>
mm/gup.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

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)))
return -EINVAL;

start = untagged_addr(start) & PAGE_MASK;
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