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

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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,

[...]

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/

> 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()?




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