userfaultfd: shmem: UFFDIO_COPY: set the page dirty if VM_WRITE is not set
authorAndrea Arcangeli <aarcange@redhat.com>
Fri, 30 Nov 2018 22:09:43 +0000 (14:09 -0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sat, 8 Dec 2018 12:03:37 +0000 (13:03 +0100)
commit46466e23bc1bc262c28a020df982233c309ed958
tree418e7fcc33bfd322c5fcbb7607d3a1e1a15dc0b5
parentaf3edb30cddfcc1eace505af10d08826a9522dbe
userfaultfd: shmem: UFFDIO_COPY: set the page dirty if VM_WRITE is not set

commit dcf7fe9d89763a28e0f43975b422ff141fe79e43 upstream.

Set the page dirty if VM_WRITE is not set because in such case the pte
won't be marked dirty and the page would be reclaimed without writepage
(i.e.  swapout in the shmem case).

This was found by source review.  Most apps (certainly including QEMU)
only use UFFDIO_COPY on PROT_READ|PROT_WRITE mappings or the app can't
modify the memory in the first place.  This is for correctness and it
could help the non cooperative use case to avoid unexpected data loss.

Link: http://lkml.kernel.org/r/20181126173452.26955-6-aarcange@redhat.com
Reviewed-by: Hugh Dickins <hughd@google.com>
Cc: stable@vger.kernel.org
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
Reported-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
mm/shmem.c