]> www.infradead.org Git - users/jedix/linux-maple.git/commit
mm/gup: disallow follow_page(FOLL_PIN)
authorDavid Hildenbrand <david@redhat.com>
Thu, 14 Apr 2022 06:06:59 +0000 (23:06 -0700)
committerakpm <akpm@linux-foundation.org>
Thu, 14 Apr 2022 06:06:59 +0000 (23:06 -0700)
commitb60790aaee3848779600f67b580528d8a41dca4f
tree57b028e4a742b4c20546e93f005df563ba8d09ac
parent80821fadde93b3358cea909dc45045dc7d8a90f9
mm/gup: disallow follow_page(FOLL_PIN)

We want to change the way we handle R/O pins on anonymous pages that might
be shared: if we detect a possibly shared anonymous page -- mapped R/O and
not !PageAnonExclusive() -- we want to trigger unsharing via a page fault,
resulting in an exclusive anonymous page that can be pinned reliably
without getting replaced via COW on the next write fault.

However, the required page fault will be problematic for follow_page(): in
contrast to ordinary GUP, follow_page() doesn't trigger faults internally.
So we would have to end up failing a R/O pin via follow_page(), although
there is something mapped R/O into the page table, which might be rather
surprising.

We don't seem to have follow_page(FOLL_PIN) users, and it's a purely
internal MM function.  Let's just make our life easier and the semantics
of follow_page() clearer by just disallowing FOLL_PIN for follow_page()
completely.

Link: https://lkml.kernel.org/r/20220329160440.193848-14-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
mm/gup.c
mm/hugetlb.c