Re: [PATCH v4 4/7] mm: replace vma->vm_flags direct modifications with modifier calls

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On Tue, Jan 31, 2023 at 12:32 AM Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> wrote:
>
> On Thu, Jan 26, 2023 at 11:37:49AM -0800, Suren Baghdasaryan wrote:
> > Replace direct modifications to vma->vm_flags with calls to modifier
> > functions to be able to track flag changes and to keep vma locking
> > correctness.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> > Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
> > Acked-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx>
> > ---
> >  arch/arm/kernel/process.c                          |  2 +-
> >  arch/ia64/mm/init.c                                |  8 ++++----
> >  arch/loongarch/include/asm/tlb.h                   |  2 +-
> >  arch/powerpc/kvm/book3s_xive_native.c              |  2 +-
> >  arch/powerpc/mm/book3s64/subpage_prot.c            |  2 +-
> >  arch/powerpc/platforms/book3s/vas-api.c            |  2 +-
> >  arch/powerpc/platforms/cell/spufs/file.c           | 14 +++++++-------
> >  arch/s390/mm/gmap.c                                |  3 +--
> >  arch/x86/entry/vsyscall/vsyscall_64.c              |  2 +-
> >  arch/x86/kernel/cpu/sgx/driver.c                   |  2 +-
> >  arch/x86/kernel/cpu/sgx/virt.c                     |  2 +-
> >  arch/x86/mm/pat/memtype.c                          |  6 +++---
> >  arch/x86/um/mem_32.c                               |  2 +-
> >  drivers/acpi/pfr_telemetry.c                       |  2 +-
> >  drivers/android/binder.c                           |  3 +--
> >  drivers/char/mspec.c                               |  2 +-
> >  drivers/crypto/hisilicon/qm.c                      |  2 +-
> >  drivers/dax/device.c                               |  2 +-
> >  drivers/dma/idxd/cdev.c                            |  2 +-
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c            |  2 +-
> >  drivers/gpu/drm/amd/amdkfd/kfd_chardev.c           |  4 ++--
> >  drivers/gpu/drm/amd/amdkfd/kfd_doorbell.c          |  4 ++--
> >  drivers/gpu/drm/amd/amdkfd/kfd_events.c            |  4 ++--
> >  drivers/gpu/drm/amd/amdkfd/kfd_process.c           |  4 ++--
> >  drivers/gpu/drm/drm_gem.c                          |  2 +-
> >  drivers/gpu/drm/drm_gem_dma_helper.c               |  3 +--
> >  drivers/gpu/drm/drm_gem_shmem_helper.c             |  2 +-
> >  drivers/gpu/drm/drm_vm.c                           |  8 ++++----
> >  drivers/gpu/drm/etnaviv/etnaviv_gem.c              |  2 +-
> >  drivers/gpu/drm/exynos/exynos_drm_gem.c            |  4 ++--
> >  drivers/gpu/drm/gma500/framebuffer.c               |  2 +-
> >  drivers/gpu/drm/i810/i810_dma.c                    |  2 +-
> >  drivers/gpu/drm/i915/gem/i915_gem_mman.c           |  4 ++--
> >  drivers/gpu/drm/mediatek/mtk_drm_gem.c             |  2 +-
> >  drivers/gpu/drm/msm/msm_gem.c                      |  2 +-
> >  drivers/gpu/drm/omapdrm/omap_gem.c                 |  3 +--
> >  drivers/gpu/drm/rockchip/rockchip_drm_gem.c        |  3 +--
> >  drivers/gpu/drm/tegra/gem.c                        |  5 ++---
> >  drivers/gpu/drm/ttm/ttm_bo_vm.c                    |  3 +--
> >  drivers/gpu/drm/virtio/virtgpu_vram.c              |  2 +-
> >  drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c           |  2 +-
> >  drivers/gpu/drm/xen/xen_drm_front_gem.c            |  3 +--
> >  drivers/hsi/clients/cmt_speech.c                   |  2 +-
> >  drivers/hwtracing/intel_th/msu.c                   |  2 +-
> >  drivers/hwtracing/stm/core.c                       |  2 +-
> >  drivers/infiniband/hw/hfi1/file_ops.c              |  4 ++--
> >  drivers/infiniband/hw/mlx5/main.c                  |  4 ++--
> >  drivers/infiniband/hw/qib/qib_file_ops.c           | 13 ++++++-------
> >  drivers/infiniband/hw/usnic/usnic_ib_verbs.c       |  2 +-
> >  drivers/infiniband/hw/vmw_pvrdma/pvrdma_verbs.c    |  2 +-
> >  .../media/common/videobuf2/videobuf2-dma-contig.c  |  2 +-
> >  drivers/media/common/videobuf2/videobuf2-vmalloc.c |  2 +-
> >  drivers/media/v4l2-core/videobuf-dma-contig.c      |  2 +-
> >  drivers/media/v4l2-core/videobuf-dma-sg.c          |  4 ++--
> >  drivers/media/v4l2-core/videobuf-vmalloc.c         |  2 +-
> >  drivers/misc/cxl/context.c                         |  2 +-
> >  drivers/misc/habanalabs/common/memory.c            |  2 +-
> >  drivers/misc/habanalabs/gaudi/gaudi.c              |  4 ++--
> >  drivers/misc/habanalabs/gaudi2/gaudi2.c            |  8 ++++----
> >  drivers/misc/habanalabs/goya/goya.c                |  4 ++--
> >  drivers/misc/ocxl/context.c                        |  4 ++--
> >  drivers/misc/ocxl/sysfs.c                          |  2 +-
> >  drivers/misc/open-dice.c                           |  4 ++--
> >  drivers/misc/sgi-gru/grufile.c                     |  4 ++--
> >  drivers/misc/uacce/uacce.c                         |  2 +-
> >  drivers/sbus/char/oradax.c                         |  2 +-
> >  drivers/scsi/cxlflash/ocxl_hw.c                    |  2 +-
> >  drivers/scsi/sg.c                                  |  2 +-
> >  drivers/staging/media/atomisp/pci/hmm/hmm_bo.c     |  2 +-
> >  drivers/staging/media/deprecated/meye/meye.c       |  4 ++--
> >  .../media/deprecated/stkwebcam/stk-webcam.c        |  2 +-
> >  drivers/target/target_core_user.c                  |  2 +-
> >  drivers/uio/uio.c                                  |  2 +-
> >  drivers/usb/core/devio.c                           |  3 +--
> >  drivers/usb/mon/mon_bin.c                          |  3 +--
> >  drivers/vdpa/vdpa_user/iova_domain.c               |  2 +-
> >  drivers/vfio/pci/vfio_pci_core.c                   |  2 +-
> >  drivers/vhost/vdpa.c                               |  2 +-
> >  drivers/video/fbdev/68328fb.c                      |  2 +-
> >  drivers/video/fbdev/core/fb_defio.c                |  4 ++--
> >  drivers/xen/gntalloc.c                             |  2 +-
> >  drivers/xen/gntdev.c                               |  4 ++--
> >  drivers/xen/privcmd-buf.c                          |  2 +-
> >  drivers/xen/privcmd.c                              |  4 ++--
> >  fs/aio.c                                           |  2 +-
> >  fs/cramfs/inode.c                                  |  2 +-
> >  fs/erofs/data.c                                    |  2 +-
> >  fs/exec.c                                          |  4 ++--
> >  fs/ext4/file.c                                     |  2 +-
> >  fs/fuse/dax.c                                      |  2 +-
> >  fs/hugetlbfs/inode.c                               |  4 ++--
> >  fs/orangefs/file.c                                 |  3 +--
> >  fs/proc/task_mmu.c                                 |  2 +-
> >  fs/proc/vmcore.c                                   |  3 +--
> >  fs/userfaultfd.c                                   |  2 +-
> >  fs/xfs/xfs_file.c                                  |  2 +-
> >  include/linux/mm.h                                 |  2 +-
> >  kernel/bpf/ringbuf.c                               |  4 ++--
> >  kernel/bpf/syscall.c                               |  4 ++--
> >  kernel/events/core.c                               |  2 +-
> >  kernel/kcov.c                                      |  2 +-
> >  kernel/relay.c                                     |  2 +-
> >  mm/madvise.c                                       |  2 +-
> >  mm/memory.c                                        |  6 +++---
> >  mm/mlock.c                                         |  6 +++---
> >  mm/mmap.c                                          | 10 +++++-----
> >  mm/mprotect.c                                      |  2 +-
> >  mm/mremap.c                                        |  6 +++---
> >  mm/nommu.c                                         | 11 ++++++-----
> >  mm/secretmem.c                                     |  2 +-
> >  mm/shmem.c                                         |  2 +-
> >  mm/vmalloc.c                                       |  2 +-
> >  net/ipv4/tcp.c                                     |  4 ++--
> >  security/selinux/selinuxfs.c                       |  6 +++---
> >  sound/core/oss/pcm_oss.c                           |  2 +-
> >  sound/core/pcm_native.c                            |  9 +++++----
> >  sound/soc/pxa/mmp-sspa.c                           |  2 +-
> >  sound/usb/usx2y/us122l.c                           |  4 ++--
> >  sound/usb/usx2y/usX2Yhwdep.c                       |  2 +-
> >  sound/usb/usx2y/usx2yhwdeppcm.c                    |  2 +-
> >  120 files changed, 188 insertions(+), 199 deletions(-)
> >
>
> Hello Suren,

Hi Hyeonggon,

>
> [...]
>
> Whoa, it's so long.
> Mostly looks fine but two things I'm not sure about:
>
> > diff --git a/drivers/misc/open-dice.c b/drivers/misc/open-dice.c
> > index 9dda47b3fd70..7be4e6c9f120 100644
> > --- a/drivers/misc/open-dice.c
> > +++ b/drivers/misc/open-dice.c
> > @@ -95,12 +95,12 @@ static int open_dice_mmap(struct file *filp, struct vm_area_struct *vma)
> >               if (vma->vm_flags & VM_WRITE)
> >                       return -EPERM;
> >               /* Ensure userspace cannot acquire VM_WRITE later. */
> > -             vma->vm_flags &= ~VM_MAYWRITE;
> > +             vm_flags_clear(vma, VM_MAYSHARE);
> >       }
>
> I think it should be:
>         s/VM_MAYSHARE/VM_MAYWRITE/

Good eye! Yes, this is definitely a bug. Will post a next version with this fix.

>
> > diff --git a/mm/mlock.c b/mm/mlock.c
> > index 5c4fff93cd6b..ed49459e343e 100644
> > --- a/mm/mlock.c
> > +++ b/mm/mlock.c
> > @@ -380,7 +380,7 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma,
> >        */
> >       if (newflags & VM_LOCKED)
> >               newflags |= VM_IO;
> > -     WRITE_ONCE(vma->vm_flags, newflags);
> > +     vm_flags_reset(vma, newflags);
> >
> >       lru_add_drain();
> >       walk_page_range(vma->vm_mm, start, end, &mlock_walk_ops, NULL);
> > @@ -388,7 +388,7 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma,
> >
> >       if (newflags & VM_IO) {
> >               newflags &= ~VM_IO;
> > -             WRITE_ONCE(vma->vm_flags, newflags);
> > +             vm_flags_reset(vma, newflags);
> >       }
> >  }
>
> wondering the if the comment above is still true?
>
>         /*
>          * There is a slight chance that concurrent page migration,
>          * or page reclaim finding a page of this now-VM_LOCKED vma,
>          * will call mlock_vma_folio() and raise page's mlock_count:
>          * double counting, leaving the page unevictable indefinitely.
>          * Communicate this danger to mlock_vma_folio() with VM_IO,
>          * which is a VM_SPECIAL flag not allowed on VM_LOCKED vmas.
>          * mmap_lock is held in write mode here, so this weird
>          * combination should not be visible to other mmap_lock users;
>          * but WRITE_ONCE so rmap walkers must see VM_IO if VM_LOCKED.
>          */
>
> does ACCESS_PRIVATE() still guarentee that compiler cannot mysteriously
> optimize writes like WRITE_ONCE()?

I don't see ACCESS_PRIVATE() providing the same guarantees as
WRITE_ONCE(), therefore I think this also needs to be changed. I'll
need to introduce something like vm_flags_reset_once() and use it
here. vm_flags_reset_once() would do WRITE_ONCE() and otherwise would
be identical to vm_flags_reset().
I'll post a new version with the fixes later today.

Thanks for the review!
Suren.

>
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