Re: [GIT PULL] MAP_SHARED_VALIDATE for 4.14

From: Dan Williams
Date: Tue Sep 19 2017 - 11:42:20 EST

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On Thu, Sep 14, 2017 at 12:44 PM, Williams, Dan J
<dan.j.williams@xxxxxxxxx> wrote:
> Hi Linus, please consider pulling:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm tags/map-shared-validate-for-4.14

Hi Linus, checking to see you if you declined to merge this because
you missed it, or you don't like the approach.

>
> ...for 4.14 as a pre-requisite for the proposed mmap flags (MAP_SYNC
> and MAP_DIRECT) being developed for 4.15 consideration. As I
> highlighted in the last posting [1] these patches are based on a random
> point in the merge window (state of the tree 2 days ago). They have not
> been in -next. However, they have been exposed to the 0day kbuild robot
> with all reports fixed. A test merge with the state of the tree today
> finds no conflicts, nor new mmap handlers for the coccinelle script to
> convert.
>
> The only change since the last posting was clarifying in commit
> 4aac0d08f6d1 "mm: introduce MAP_SHARED_VALIDATE..." that
> MAP_SHARED_VALIDATE is just MAP_SHARED+validate, not a bitmap to be
> added to new flag values, and that it is a unique MAP_TYPE number not
> necessarily (MAP_SHARED|MAP_PRIVATE) (from Jan's review).
>
> Now, we could wait until 4.15 and do the same rebase, run coccinelle
> script, rinse, and repeat process for 4.15. I.e wait until we also have
> the MAP_SYNC and/or MAP_DIRECT to merge at the same time, but I think
> it is preferable to base that development on early 4.14-rc and get it
> some soak time in -next.
>
> Another alternative is to just get patch1, commit 403fee48224c "vfs:
> add flags...", in for 4.14 and save MAP_SHARED_VALIDATE to arrive in
> the next merge window coincident with the new flags implementation.
>
> Lastly, the alternative to all this thrash is carrying the flags in the
> vma. That bloats vm_area_struct everywhere and complicates vma
> splitting / merging for the handful of mmap implementations that will
> ever care about the new flags.
>
> [1]: https://lwn.net/Articles/733281/
>
> ---
>
> The following changes since commit 8fac2f96ab86b0e14ec4e42851e21e9b518bdc55:
>
> Merge branch 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm (2017-09-12 06:10:44 -0700)
>
> are available in the git repository at:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm tags/map-shared-validate-for-4.14
>
> for you to fetch changes up to 4aac0d08f6d1ae4475bbfe761b943d105e11b82a:
>
> mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags (2017-09-12 10:12:34 -0700)
>
> ----------------------------------------------------------------
> MAP_SHARED_VALIDATE for 4.14
>
> Preparation infrastructure for introducing new mmap flags:
>
> * Introduce MAP_SHARED_VALIDATE as an mmap(2) flag that in addition to
> creating a MAP_SHARED mapping also arranges for the @flags parameter
> of mmap(2) to be validated by the endpoint mmap-file-operation. I.e.
> new mmap flags require per mmap implementation opt-in and run time
> validation.
>
> * Make the @flags parameter available to all mmap implementations, both
> top-level 'struct file_operations' and sub-level leaf implementations.
>
> ----------------------------------------------------------------
> Dan Williams (2):
> vfs: add flags parameter to all ->mmap() handlers
> mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags
>
> arch/alpha/include/uapi/asm/mman.h | 1 +
> arch/arc/kernel/arc_hostlink.c | 3 +-
> arch/mips/include/uapi/asm/mman.h | 1 +
> arch/mips/kernel/vdso.c | 2 +-
> arch/parisc/include/uapi/asm/mman.h | 1 +
> arch/powerpc/kernel/proc_powerpc.c | 3 +-
> arch/powerpc/kvm/book3s_64_vio.c | 3 +-
> arch/powerpc/platforms/cell/spufs/file.c | 21 +++++++----
> arch/powerpc/platforms/powernv/memtrace.c | 3 +-
> arch/powerpc/platforms/powernv/opal-prd.c | 3 +-
> arch/tile/mm/elf.c | 3 +-
> arch/um/drivers/mmapper_kern.c | 3 +-
> arch/xtensa/include/uapi/asm/mman.h | 1 +
> drivers/android/binder.c | 3 +-
> drivers/auxdisplay/cfag12864bfb.c | 3 +-
> drivers/auxdisplay/ht16k33.c | 3 +-
> drivers/char/agp/frontend.c | 3 +-
> drivers/char/bsr.c | 3 +-
> drivers/char/hpet.c | 6 ++-
> drivers/char/mbcs.c | 3 +-
> drivers/char/mbcs.h | 3 +-
> drivers/char/mem.c | 11 ++++--
> drivers/char/mspec.c | 9 +++--
> drivers/char/uv_mmtimer.c | 6 ++-
> drivers/dax/device.c | 3 +-
> drivers/dma-buf/dma-buf.c | 11 ++++--
> drivers/firewire/core-cdev.c | 3 +-
> drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 3 +-
> drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h | 3 +-
> drivers/gpu/drm/amd/amdkfd/kfd_chardev.c | 5 ++-
> drivers/gpu/drm/armada/armada_gem.c | 3 +-
> drivers/gpu/drm/ast/ast_drv.h | 3 +-
> drivers/gpu/drm/ast/ast_ttm.c | 3 +-
> drivers/gpu/drm/bochs/bochs.h | 3 +-
> drivers/gpu/drm/bochs/bochs_fbdev.c | 2 +-
> drivers/gpu/drm/bochs/bochs_mm.c | 3 +-
> drivers/gpu/drm/cirrus/cirrus_drv.h | 3 +-
> drivers/gpu/drm/cirrus/cirrus_ttm.c | 3 +-
> drivers/gpu/drm/drm_fb_cma_helper.c | 8 ++--
> drivers/gpu/drm/drm_gem.c | 4 +-
> drivers/gpu/drm/drm_gem_cma_helper.c | 8 ++--
> drivers/gpu/drm/drm_prime.c | 5 ++-
> drivers/gpu/drm/drm_vm.c | 3 +-
> drivers/gpu/drm/etnaviv/etnaviv_drv.h | 6 ++-
> drivers/gpu/drm/etnaviv/etnaviv_gem.c | 11 +++---
> drivers/gpu/drm/etnaviv/etnaviv_gem.h | 3 +-
> drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c | 9 +++--
> drivers/gpu/drm/exynos/exynos_drm_fbdev.c | 2 +-
> drivers/gpu/drm/exynos/exynos_drm_gem.c | 10 +++--
> drivers/gpu/drm/exynos/exynos_drm_gem.h | 6 ++-
> drivers/gpu/drm/gma500/framebuffer.c | 3 +-
> drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.h | 3 +-
> drivers/gpu/drm/hisilicon/hibmc/hibmc_ttm.c | 3 +-
> drivers/gpu/drm/i810/i810_dma.c | 3 +-
> drivers/gpu/drm/i915/i915_gem_dmabuf.c | 6 ++-
> drivers/gpu/drm/i915/selftests/mock_dmabuf.c | 4 +-
> drivers/gpu/drm/mediatek/mtk_drm_gem.c | 8 ++--
> drivers/gpu/drm/mediatek/mtk_drm_gem.h | 5 ++-
> drivers/gpu/drm/mgag200/mgag200_drv.h | 3 +-
> drivers/gpu/drm/mgag200/mgag200_ttm.c | 3 +-
> drivers/gpu/drm/msm/msm_drv.h | 6 ++-
> drivers/gpu/drm/msm/msm_fbdev.c | 6 ++-
> drivers/gpu/drm/msm/msm_gem.c | 5 ++-
> drivers/gpu/drm/msm/msm_gem_prime.c | 3 +-
> drivers/gpu/drm/nouveau/nouveau_ttm.c | 5 ++-
> drivers/gpu/drm/nouveau/nouveau_ttm.h | 2 +-
> drivers/gpu/drm/omapdrm/omap_drv.h | 3 +-
> drivers/gpu/drm/omapdrm/omap_gem.c | 5 ++-
> drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c | 2 +-
> drivers/gpu/drm/qxl/qxl_drv.h | 6 ++-
> drivers/gpu/drm/qxl/qxl_prime.c | 2 +-
> drivers/gpu/drm/qxl/qxl_ttm.c | 3 +-
> drivers/gpu/drm/radeon/radeon_drv.c | 3 +-
> drivers/gpu/drm/radeon/radeon_ttm.c | 3 +-
> drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c | 5 ++-
> drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 7 ++--
> drivers/gpu/drm/rockchip/rockchip_drm_gem.h | 5 ++-
> drivers/gpu/drm/tegra/gem.c | 9 +++--
> drivers/gpu/drm/tegra/gem.h | 3 +-
> drivers/gpu/drm/udl/udl_dmabuf.c | 3 +-
> drivers/gpu/drm/udl/udl_drv.h | 3 +-
> drivers/gpu/drm/udl/udl_fb.c | 3 +-
> drivers/gpu/drm/udl/udl_gem.c | 5 ++-
> drivers/gpu/drm/vc4/vc4_bo.c | 10 +++--
> drivers/gpu/drm/vc4/vc4_drv.h | 6 ++-
> drivers/gpu/drm/vgem/vgem_drv.c | 10 +++--
> drivers/gpu/drm/virtio/virtgpu_drv.h | 6 ++-
> drivers/gpu/drm/virtio/virtgpu_prime.c | 2 +-
> drivers/gpu/drm/virtio/virtgpu_ttm.c | 3 +-
> drivers/gpu/drm/vmwgfx/vmwgfx_drv.h | 3 +-
> drivers/gpu/drm/vmwgfx/vmwgfx_prime.c | 3 +-
> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c | 3 +-
> drivers/hsi/clients/cmt_speech.c | 3 +-
> drivers/hwtracing/intel_th/msu.c | 3 +-
> drivers/hwtracing/stm/core.c | 3 +-
> drivers/infiniband/core/uverbs_main.c | 3 +-
> drivers/infiniband/hw/hfi1/file_ops.c | 6 ++-
> drivers/infiniband/hw/qib/qib_file_ops.c | 5 ++-
> drivers/media/common/saa7146/saa7146_fops.c | 3 +-
> drivers/media/pci/bt8xx/bttv-driver.c | 3 +-
> drivers/media/pci/cx18/cx18-fileops.c | 3 +-
> drivers/media/pci/cx18/cx18-fileops.h | 3 +-
> drivers/media/pci/meye/meye.c | 3 +-
> drivers/media/pci/zoran/zoran_driver.c | 2 +-
> drivers/media/platform/davinci/vpfe_capture.c | 3 +-
> drivers/media/platform/exynos-gsc/gsc-m2m.c | 3 +-
> drivers/media/platform/fsl-viu.c | 3 +-
> drivers/media/platform/m2m-deinterlace.c | 3 +-
> drivers/media/platform/mx2_emmaprp.c | 3 +-
> drivers/media/platform/omap/omap_vout.c | 3 +-
> drivers/media/platform/omap3isp/ispvideo.c | 3 +-
> drivers/media/platform/s3c-camif/camif-capture.c | 3 +-
> drivers/media/platform/s5p-mfc/s5p_mfc.c | 3 +-
> drivers/media/platform/sh_veu.c | 3 +-
> drivers/media/platform/soc_camera/soc_camera.c | 3 +-
> drivers/media/platform/via-camera.c | 3 +-
> drivers/media/usb/cpia2/cpia2_v4l.c | 3 +-
> drivers/media/usb/cx231xx/cx231xx-417.c | 3 +-
> drivers/media/usb/cx231xx/cx231xx-video.c | 3 +-
> drivers/media/usb/gspca/gspca.c | 3 +-
> drivers/media/usb/stkwebcam/stk-webcam.c | 3 +-
> drivers/media/usb/tm6000/tm6000-video.c | 3 +-
> drivers/media/usb/usbvision/usbvision-video.c | 3 +-
> drivers/media/usb/uvc/uvc_v4l2.c | 3 +-
> drivers/media/usb/zr364xx/zr364xx.c | 3 +-
> drivers/media/v4l2-core/v4l2-dev.c | 5 ++-
> drivers/media/v4l2-core/v4l2-mem2mem.c | 3 +-
> drivers/media/v4l2-core/videobuf2-dma-contig.c | 2 +-
> drivers/media/v4l2-core/videobuf2-dma-sg.c | 2 +-
> drivers/media/v4l2-core/videobuf2-v4l2.c | 3 +-
> drivers/media/v4l2-core/videobuf2-vmalloc.c | 2 +-
> drivers/misc/aspeed-lpc-ctrl.c | 3 +-
> drivers/misc/cxl/api.c | 5 ++-
> drivers/misc/cxl/cxl.h | 3 +-
> drivers/misc/cxl/file.c | 3 +-
> drivers/misc/genwqe/card_dev.c | 3 +-
> drivers/misc/mic/scif/scif_fd.c | 3 +-
> drivers/misc/mic/vop/vop_vringh.c | 3 +-
> drivers/misc/sgi-gru/grufile.c | 3 +-
> drivers/mtd/mtdchar.c | 3 +-
> drivers/pci/proc.c | 3 +-
> drivers/rapidio/devices/rio_mport_cdev.c | 3 +-
> drivers/sbus/char/flash.c | 3 +-
> drivers/sbus/char/jsflash.c | 3 +-
> drivers/scsi/cxlflash/superpipe.c | 5 ++-
> drivers/scsi/sg.c | 3 +-
> drivers/staging/android/ashmem.c | 3 +-
> drivers/staging/android/ion/ion.c | 3 +-
> drivers/staging/comedi/comedi_fops.c | 3 +-
> .../staging/lustre/lustre/llite/llite_internal.h | 3 +-
> drivers/staging/lustre/lustre/llite/llite_mmap.c | 5 ++-
> .../media/atomisp/pci/atomisp2/atomisp_fops.c | 6 ++-
> drivers/staging/media/davinci_vpfe/vpfe_video.c | 3 +-
> drivers/staging/media/omap4iss/iss_video.c | 3 +-
> drivers/staging/vboxvideo/vbox_drv.h | 5 ++-
> drivers/staging/vboxvideo/vbox_prime.c | 3 +-
> drivers/staging/vboxvideo/vbox_ttm.c | 3 +-
> drivers/staging/vme/devices/vme_user.c | 3 +-
> drivers/tee/tee_shm.c | 3 +-
> drivers/uio/uio.c | 3 +-
> drivers/usb/core/devio.c | 3 +-
> drivers/usb/gadget/function/uvc_v4l2.c | 3 +-
> drivers/usb/mon/mon_bin.c | 3 +-
> drivers/vfio/vfio.c | 7 +++-
> drivers/video/fbdev/68328fb.c | 6 ++-
> drivers/video/fbdev/amba-clcd.c | 2 +-
> drivers/video/fbdev/aty/atyfb_base.c | 6 ++-
> drivers/video/fbdev/au1100fb.c | 3 +-
> drivers/video/fbdev/au1200fb.c | 3 +-
> drivers/video/fbdev/bw2.c | 5 ++-
> drivers/video/fbdev/cg14.c | 5 ++-
> drivers/video/fbdev/cg3.c | 5 ++-
> drivers/video/fbdev/cg6.c | 5 ++-
> drivers/video/fbdev/controlfb.c | 4 +-
> drivers/video/fbdev/core/fb_defio.c | 3 +-
> drivers/video/fbdev/core/fbmem.c | 5 ++-
> drivers/video/fbdev/ep93xx-fb.c | 3 +-
> drivers/video/fbdev/fb-puv3.c | 2 +-
> drivers/video/fbdev/ffb.c | 5 ++-
> drivers/video/fbdev/gbefb.c | 2 +-
> drivers/video/fbdev/igafb.c | 2 +-
> drivers/video/fbdev/leo.c | 5 ++-
> drivers/video/fbdev/omap/omapfb_main.c | 3 +-
> drivers/video/fbdev/omap2/omapfb/omapfb-main.c | 3 +-
> drivers/video/fbdev/p9100.c | 6 ++-
> drivers/video/fbdev/ps3fb.c | 3 +-
> drivers/video/fbdev/pxa3xx-gcu.c | 3 +-
> drivers/video/fbdev/sa1100fb.c | 2 +-
> drivers/video/fbdev/sh_mobile_lcdcfb.c | 6 ++-
> drivers/video/fbdev/smscufx.c | 3 +-
> drivers/video/fbdev/tcx.c | 5 ++-
> drivers/video/fbdev/udlfb.c | 3 +-
> drivers/video/fbdev/vermilion/vermilion.c | 3 +-
> drivers/video/fbdev/vfb.c | 4 +-
> drivers/xen/gntalloc.c | 3 +-
> drivers/xen/gntdev.c | 3 +-
> drivers/xen/privcmd.c | 3 +-
> drivers/xen/xenbus/xenbus_dev_backend.c | 3 +-
> drivers/xen/xenfs/xenstored.c | 3 +-
> fs/9p/vfs_file.c | 10 +++--
> fs/aio.c | 3 +-
> fs/btrfs/file.c | 4 +-
> fs/ceph/addr.c | 3 +-
> fs/ceph/super.h | 3 +-
> fs/cifs/cifsfs.h | 6 ++-
> fs/cifs/file.c | 10 +++--
> fs/coda/file.c | 5 ++-
> fs/ecryptfs/file.c | 5 ++-
> fs/ext2/file.c | 5 ++-
> fs/ext4/file.c | 3 +-
> fs/f2fs/file.c | 3 +-
> fs/fuse/file.c | 8 ++--
> fs/gfs2/file.c | 3 +-
> fs/hugetlbfs/inode.c | 3 +-
> fs/kernfs/file.c | 3 +-
> fs/ncpfs/mmap.c | 3 +-
> fs/ncpfs/ncp_fs.h | 2 +-
> fs/nfs/file.c | 5 ++-
> fs/nfs/internal.h | 2 +-
> fs/nilfs2/file.c | 3 +-
> fs/ocfs2/mmap.c | 3 +-
> fs/ocfs2/mmap.h | 3 +-
> fs/orangefs/file.c | 5 ++-
> fs/proc/inode.c | 7 ++--
> fs/proc/vmcore.c | 6 ++-
> fs/ramfs/file-nommu.c | 6 ++-
> fs/romfs/mmap-nommu.c | 3 +-
> fs/ubifs/file.c | 5 ++-
> fs/xfs/xfs_file.c | 2 +-
> include/drm/drm_drv.h | 3 +-
> include/drm/drm_gem.h | 3 +-
> include/drm/drm_gem_cma_helper.h | 6 ++-
> include/drm/drm_legacy.h | 3 +-
> include/linux/dma-buf.h | 5 ++-
> include/linux/fb.h | 6 ++-
> include/linux/fs.h | 14 ++++---
> include/linux/mm.h | 2 +-
> include/linux/mman.h | 44 ++++++++++++++++++++++
> include/media/v4l2-dev.h | 2 +-
> include/media/v4l2-mem2mem.h | 3 +-
> include/media/videobuf2-v4l2.h | 3 +-
> include/misc/cxl.h | 3 +-
> include/uapi/asm-generic/mman-common.h | 1 +
> ipc/shm.c | 5 ++-
> kernel/events/core.c | 3 +-
> kernel/kcov.c | 3 +-
> kernel/relay.c | 4 +-
> mm/filemap.c | 15 +++++---
> mm/mmap.c | 14 +++++--
> mm/nommu.c | 4 +-
> mm/shmem.c | 3 +-
> net/socket.c | 6 ++-
> security/selinux/selinuxfs.c | 6 ++-
> sound/core/compress_offload.c | 3 +-
> sound/core/hwdep.c | 3 +-
> sound/core/info.c | 3 +-
> sound/core/init.c | 3 +-
> sound/core/oss/pcm_oss.c | 3 +-
> sound/core/pcm_native.c | 3 +-
> sound/oss/soundcard.c | 3 +-
> sound/oss/swarm_cs4297a.c | 3 +-
> tools/include/uapi/asm-generic/mman-common.h | 1 +
> virt/kvm/kvm_main.c | 3 +-
> 263 files changed, 722 insertions(+), 374 deletions(-)
>
> commit 403fee48224c8fd236a9ec23461e2d752c79101f
> Author: Dan Williams <dan.j.williams@xxxxxxxxx>
> Date: Tue Sep 5 17:28:59 2017 -0700
>
> vfs: add flags parameter to all ->mmap() handlers
>
> We are running running short of vma->vm_flags. We can avoid needing a
> new VM_* flag in some cases if the original @flags submitted to mmap(2)
> is made available to the ->mmap() 'struct file_operations'
> implementation. For example, the proposed addition of MAP_DIRECT can be
> implemented without taking up a new vm_flags bit. Another motivation to
> avoid vm_flags is that they appear in /proc/$pid/smaps, and we have seen
> software that tries to dangerously (TOCTOU) read smaps to infer the
> behavior of a virtual address range. Lastly, we may want to reject mmap
> attempts on a per-mmap-call basis.
>
> This conversion was performed by the following semantic patch. There
> were a few manual edits for oddities like proc_reg_mmap, call_mmap,
> drm_gem_cma_mmap, and cxl_fd_mmap.
>
> Thanks to Julia for helping me with coccinelle iteration to cover cases
> where the mmap routine is defined in a separate file from the operations
> instance that consumes it.
>
> // Usage:
> // spatch mmap.cocci --no-includes --include-headers --in-place ./ -j 40 --very-quiet
>
> virtual after_start
>
> @initialize:ocaml@
> @@
>
> let tbl = Hashtbl.create(100)
>
> let add_if_not_present fn =
> if not(Hashtbl.mem tbl fn) then Hashtbl.add tbl fn ()
>
> @ a @
> identifier fn;
> identifier ops;
> expression E1;
> @@
>
> (
> struct file_operations ops = { ..., .mmap = fn, ...};
> |
> struct file_operations ops[E1] = { ..., { ..., .mmap = fn, ...}, ...};
> |
> struct etnaviv_gem_ops ops = { ..., .mmap = fn, ...};
> |
> struct dma_buf_ops ops = { ..., .mmap = fn, ...};
> |
> struct drm_driver ops = { ..., .gem_prime_mmap = fn, ...};
> |
> struct fb_ops ops = { ..., .fb_mmap = fn, ...};
> |
> struct v4l2_file_operations ops = { ..., .mmap = fn, ...};
> )
>
> @script:ocaml@
> fn << a.fn;
> @@
>
> add_if_not_present fn
>
> @finalize:ocaml depends on !after_start@
> tbls << merge.tbl;
> @@
>
> List.iter (fun t -> Hashtbl.iter (fun f _ -> add_if_not_present f) t) tbls;
> Hashtbl.iter
> (fun f _ ->
> let it = new iteration() in
> it#add_virtual_rule After_start;
> it#add_virtual_identifier Fn f;
> it#register())
> tbl
>
> @depends on after_start@
> identifier virtual.fn;
> identifier x, y;
> type T;
> @@
>
> int fn(T *x,
> struct vm_area_struct *y
> - )
> + , unsigned long map_flags)
> {
> ...
> }
>
> @depends on after_start@
> identifier virtual.fn;
> identifier x, y;
> type T;
> @@
>
> int fn(T *x,
> struct vm_area_struct *y
> - );
> + , unsigned long map_flags);
>
> @depends on after_start@
> identifier virtual.fn;
> type T;
>
> @@
>
> int fn(T *,
> struct vm_area_struct *
> - );
> + , unsigned long);
>
> @depends on after_start@
> identifier virtual.fn;
> expression E1, E2, E3;
> @@
>
> E3 = fn(E1, E2
> - );
> + , map_flags);
>
> @depends on after_start@
> identifier virtual.fn;
> expression E1, E2;
> @@
>
> return fn(E1, E2
> - );
> + , map_flags);
>
> Cc: Takashi Iwai <tiwai@xxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: David Airlie <airlied@xxxxxxxx>
> Cc: <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>
> Cc: <linux-media@xxxxxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Suggested-by: Jan Kara <jack@xxxxxxx>
> Acked-by: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Julia Lawall <julia.lawall@xxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
>
> commit 4aac0d08f6d1ae4475bbfe761b943d105e11b82a
> Author: Dan Williams <dan.j.williams@xxxxxxxxx>
> Date: Mon Aug 14 14:59:39 2017 -0700
>
> mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags
>
> The mmap(2) syscall suffers from the ABI anti-pattern of not validating
> unknown flags. However, proposals like MAP_SYNC and MAP_DIRECT need a
> mechanism to define new behavior that is known to fail on older kernels
> without the support. Define a new MAP_SHARED_VALIDATE flag pattern that
> is guaranteed to fail on all legacy mmap implementations.
>
> It is worth noting that the original proposal was for a standalone
> MAP_VALIDATE flag. However, when that could not be supported by all
> archs Linus observed:
>
> I see why you *think* you want a bitmap. You think you want
> a bitmap because you want to make MAP_VALIDATE be part of MAP_SYNC
> etc, so that people can do
>
> ret = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED
> | MAP_SYNC, fd, 0);
>
> and "know" that MAP_SYNC actually takes.
>
> And I'm saying that whole wish is bogus. You're fundamentally
> depending on special semantics, just make it explicit. It's already
> not portable, so don't try to make it so.
>
> Rename that MAP_VALIDATE as MAP_SHARED_VALIDATE, make it have a value
> of 0x3, and make people do
>
> ret = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED_VALIDATE
> | MAP_SYNC, fd, 0);
>
> and then the kernel side is easier too (none of that random garbage
> playing games with looking at the "MAP_VALIDATE bit", but just another
> case statement in that map type thing.
>
> Boom. Done.
>
> Similar to ->fallocate() we also want the ability to validate the
> support for new flags on a per ->mmap() 'struct file_operations'
> instance basis. Towards that end arrange for flags to be generically
> validated against a mmap_supported_mask exported by 'struct
> file_operations'. By default all existing flags are implicitly
> supported, but new flags require MAP_SHARED_VALIDATE and
> per-instance-opt-in.
>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Suggested-by: Christoph Hellwig <hch@xxxxxx>
> Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> _______________________________________________
> Linux-nvdimm mailing list
> Linux-nvdimm@xxxxxxxxxxxx
> https://lists.01.org/mailman/listinfo/linux-nvdimm

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