• Andrea Arcangeli's avatar
    userfaultfd: use ENOENT instead of EFAULT if the atomic copy user fails · 9e368259
    Andrea Arcangeli authored
    Patch series "userfaultfd shmem updates".
    
    Jann found two bugs in the userfaultfd shmem MAP_SHARED backend: the
    lack of the VM_MAYWRITE check and the lack of i_size checks.
    
    Then looking into the above we also fixed the MAP_PRIVATE case.
    
    Hugh by source review also found a data loss source if UFFDIO_COPY is
    used on shmem MAP_SHARED PROT_READ mappings (the production usages
    incidentally run with PROT_READ|PROT_WRITE, so the data loss couldn't
    happen in those production usages like with QEMU).
    
    The whole patchset is marked for stable.
    
    We verified QEMU postcopy live migration with guest running on shmem
    MAP_PRIVATE run as well as before after the fix of shmem MAP_PRIVATE.
    Regardless if it's shmem or hugetlbfs or MAP_PRIVATE or MAP_SHARED, QEMU
    unconditionally invokes a punch hole if the guest mapping is filebacked
    and a MADV_DONTNEED too (needed to get rid of the MAP_PRIVATE COWs and
    for the anon backend).
    
    This patch (of 5):
    
    We internally used EFAULT to communicate with the caller, switch to
    ENOENT, so EFAULT can be used as a non internal retval.
    
    Link: http://lkml.kernel.org/r/20181126173452.26955-2-aarcange@redhat.com
    Fixes: 4c27fe4c
    
     ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
    Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
    Reviewed-by: default avatarMike Rapoport <rppt@linux.ibm.com>
    Reviewed-by: default avatarHugh Dickins <hughd@google.com>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    Cc: Jann Horn <jannh@google.com>
    Cc: Peter Xu <peterx@redhat.com>
    Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
    Cc: <stable@vger.kernel.org>
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    9e368259
userfaultfd.c 15 KB