The patch titled
Subject: mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path
has been added to the -mm tree. Its filename is
mm-gup-fix-omission-of-check-on-foll_longterm-in-gup-fast-path.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-gup-fix-omission-of-check-on-foll_longterm-in-gup-fast-path.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-gup-fix-omission-of-check-on-foll_longterm-in-gup-fast-path.patch
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------------------------------------------------------
From: Pingfan Liu <kernelfans@xxxxxxxxx>
Subject: mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path
FOLL_LONGTERM is a special case of FOLL_PIN. It suggests a pin which is
going to be given to hardware and can't move. It would truncate CMA
permanently and should be excluded.
In gup slow path, where
__gup_longterm_locked->check_and_migrate_cma_pages() handles
FOLL_LONGTERM, but in fast path, there lacks such a check, which means a
possible leak of CMA page to longterm pinned.
Place a check in try_grab_compound_head() in the fast path to fix the
leak, and if FOLL_LONGTERM happens on CMA, it will fall back to slow path
to migrate the page.
Some note about the check: Huge page's subpages have the same migrate type
due to either allocation from a free_list[] or alloc_contig_range() with
param MIGRATE_MOVABLE. So it is enough to check on a single subpage by
is_migrate_cma_page(subpage)
Link: http://lkml.kernel.org/r/1584876733-17405-3-git-send-email-kernelfans@xxxxxxxxx
Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/mm/gup.c~mm-gup-fix-omission-of-check-on-foll_longterm-in-gup-fast-path
+++ a/mm/gup.c
@@ -89,6 +89,14 @@ static __maybe_unused struct page *try_g
int orig_refs = refs;
/*
+ * Can't do FOLL_LONGTERM + FOLL_PIN with CMA in the gup fast
+ * path, so fail and let the caller fall back to the slow path.
+ */
+ if (unlikely(flags & FOLL_LONGTERM) &&
+ is_migrate_cma_page(page))
+ return NULL;
+
+ /*
* When pinning a compound page of order > 1 (which is what
* hpage_pincount_available() checks for), use an exact count to
* track it, via hpage_pincount_add/_sub().
_
Patches currently in -mm which might be from kernelfans@xxxxxxxxx are
mm-gup-rename-nr-as-nr_pinned-in-get_user_pages_fast.patch
mm-gup-fix-omission-of-check-on-foll_longterm-in-gup-fast-path.patch
mm-sparse-rename-pfn_present-as-pfn_in_present_section.patch
