From: John Hubbard <jhubbard@xxxxxxxxxx>
Subject: 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().
Link: http://lkml.kernel.org/r/20200107224558.2362728-9-jhubbard@xxxxxxxxxx
Fixes: 817be129e6f2 ("mm: validate get_user_pages_fast flags")
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Reviewed-by: Leon Romanovsky <leonro@xxxxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Björn Töpel <bjorn.topel@xxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/mm/gup.c~mm-gup-allow-foll_force-for-get_user_pages_fast
+++ a/mm/gup.c
@@ -2411,7 +2411,8 @@ int get_user_pages_fast(unsigned long st
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;
_
