linux-kernel - [RFC PATCH 0/5] userfaultfd: non-cooperative: better tracking for mapping changes

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Date:   Tue, 24 Jan 2017 15:51:58 +0200
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     Linux-MM <linux-mm@...ck.org>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>
Subject: [RFC PATCH 0/5] userfaultfd: non-cooperative: better tracking for mapping changes

Hi,

These patches try to address issues I've encountered during integration of
userfaultfd with CRIU.
Previously added userfaultfd events for fork(), madvise() and mremap()
unfortunately do not cover all possible changes to a process virtual memory
layout required for uffd monitor.
When one or more VMAs is removed from the process mm, the external uffd
monitor has no way to detect those changes and will attempt to fill the
removed regions with userfaultfd_copy.
Another problematic event is the exit() of the process. Here again, the
external uffd monitor will try to use userfaultfd_copy, although mm owning
the memory has already gone.

The first patch in the series is a minor cleanup and it's not strictly
related to the rest of the series.

The patches 2 and 3 below add UFFD_EVENT_UNMAP and UFFD_EVENT_EXIT to allow
the uffd monitor track changes in the memory layout of a process.

The patches 4 and 5 amend error codes returned by userfaultfd_copy to make
the uffd monitor able to cope with races that might occur between delivery
of unmap and exit events and outstanding userfaultfd_copy's.

The patches are agains current -mm tree.

Mike Rapoport (5):
  mm: call vm_munmap in munmap syscall instead of using open coded version
  userfaultfd: non-cooperative: add event for memory unmaps
  userfaultfd: non-cooperative: add event for exit() notification
  userfaultfd: mcopy_atomic: return -ENOENT when no compatible VMA found
  userfaultfd_copy: return -ENOSPC in case mm has gone

 arch/tile/mm/elf.c               |  2 +-
 arch/x86/entry/vdso/vma.c        |  2 +-
 arch/x86/mm/mpx.c                |  2 +-
 fs/aio.c                         |  2 +-
 fs/proc/vmcore.c                 |  4 +-
 fs/userfaultfd.c                 | 91 ++++++++++++++++++++++++++++++++++++++++
 include/linux/mm.h               | 14 ++++---
 include/linux/userfaultfd_k.h    | 25 +++++++++++
 include/uapi/linux/userfaultfd.h |  8 +++-
 ipc/shm.c                        |  6 +--
 kernel/exit.c                    |  2 +
 mm/mmap.c                        | 55 ++++++++++++++----------
 mm/mremap.c                      | 23 ++++++----
 mm/userfaultfd.c                 | 42 ++++++++++---------
 mm/util.c                        |  5 ++-
 15 files changed, 215 insertions(+), 68 deletions(-)

-- 
1.9.1