[v12,08/22] mm/gup: allow FOLL_FORCE for get_user_pages_fast()
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Message ID 20200107224558.2362728-9-jhubbard@nvidia.com
State New
Headers show
Series
  • mm/gup: prereqs to track dma-pinned pages: FOLL_PIN
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Commit Message

John Hubbard Jan. 7, 2020, 10:45 p.m. UTC
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>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Christoph Hellwig Jan. 15, 2020, 3:25 p.m. UTC | #1
Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Patch
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diff --git a/mm/gup.c b/mm/gup.c
index b61bd5c469ae..a594bc708367 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2411,7 +2411,8 @@  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;