[PATCH v6 0/5] MAP_DIRECT and block-map-atomic files

Dan Williams
2017-08-23T23:55:02Z

Changes since v5 [1]:
* Compile fixes from a much improved coccinelle semantic patch (thanks
Julia!) that adds a 'flags' argument to all the ->mmap()
implementations in the kernel. (0day-kbuild-robot)

* Make the deprecated MAP_DENYWRITE and MAP_EXECUTABLE flags return
EOPNOTSUPP with the new mmap3() syscall. (Kirill)

* Minor changelog updates.

* Updated cover letter with a clarified summary and checklist of
questions to answer before proceeding further.

---

MAP_DIRECT is a mechanism to ask the kernel to atomically manage the
file-offset to physical-address block relationship of a mapping relative
to any memory-mapped access. It is complimentary to the proposed
MAP_SYNC mechanism which makes the same guarantee relative to cpu
faults. MAP_DIRECT goes a step further and makes this guarantee for
agents that may not generate mmu faults, but at the cost of restricting
the kernel's ability to mutate the block-map at will.

MAP_SYNC is preferred for scenarios that want full filesystem feature
support while avoiding fsync/msync overhead, but also do not need to
contend with hypervisors or RDMA agents that do not give the kernel an
mmu fault. In other words, the need for MAP_DIRECT is driven by the
scarcity of SVM capable hardware (Shared Virtual Memory, where hardware
generates mmu faults), hypervisors like Xen that need to interrogate the
physical address layout of a file to maintain their own physical-address
mapping metadata outside the kernel, and peer-to-peer DMA use cases that
always bypass the mmu.

The MAP_DIRECT mechanism allows a filesystem to be used for capacity
provisioning and access control where these aforementioned applications
would otherwise be forced to roll a custom solution on top of a raw
device-file.

Questions:
1/ Is the definition of MAP_DIRECT constrained enough to allow us to
make the restrictions it imposes on the kernel finer grained over time?

2/ Do the XFS changes look sane? They attempt to avoid adding any
overhead to the non-MAP_DIRECT case at the expense of the new
i_mapdcount atomic counter in the XFS inode.

3/ While the generic MAP_DIRECT description warns that the block-map may
not be actually be immutable for the lifetime of the mapping it also
does not preclude a filesystem from making that guarantee. In fact,
Dave wants to be able to get a stable view of the physical mapping
[2], and Xen has a need to do the same [3]. Do we want userspace to
start making "XFS + MAP_DIRECT == Immutable" assumptions, or do we
need a separate mechanism for that guarantee?

[1]: https://lkml.org/lkml/2017/8/16/114
[2]: https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1467677.html
[3]: https://lists.xen.org/archives/html/xen-devel/2017-04/msg00419.html

---

Dan Williams (5):
vfs: add flags parameter to ->mmap() in 'struct file_operations'
fs, xfs: introduce S_IOMAP_SEALED
mm: introduce mmap3 for safely defining new mmap flags
fs, xfs: introduce MAP_DIRECT for creating block-map-atomic file ranges
fs, fcntl: add F_MAP_DIRECT

arch/arc/kernel/arc_hostlink.c | 3 -
arch/mips/kernel/vdso.c | 2
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/opal-prd.c | 3 -
arch/um/drivers/mmapper_kern.c | 3 -
arch/x86/entry/syscalls/syscall_32.tbl | 1
arch/x86/entry/syscalls/syscall_64.tbl | 1
drivers/android/binder.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 | 4 +
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/arc/arcpgu_drv.c | 5 +
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_mm.c | 3 -
drivers/gpu/drm/cirrus/cirrus_drv.h | 3 -
drivers/gpu/drm/cirrus/cirrus_ttm.c | 3 -
drivers/gpu/drm/drm_gem.c | 3 -
drivers/gpu/drm/drm_gem_cma_helper.c | 6 +
drivers/gpu/drm/drm_vm.c | 3 -
drivers/gpu/drm/etnaviv/etnaviv_drv.h | 3 -
drivers/gpu/drm/etnaviv/etnaviv_gem.c | 5 +
drivers/gpu/drm/exynos/exynos_drm_gem.c | 5 +
drivers/gpu/drm/exynos/exynos_drm_gem.h | 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 | 2
drivers/gpu/drm/mediatek/mtk_drm_gem.c | 5 +
drivers/gpu/drm/mediatek/mtk_drm_gem.h | 3 -
drivers/gpu/drm/mgag200/mgag200_drv.h | 3 -
drivers/gpu/drm/mgag200/mgag200_ttm.c | 3 -
drivers/gpu/drm/msm/msm_drv.h | 3 -
drivers/gpu/drm/msm/msm_gem.c | 5 +
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/qxl/qxl_drv.h | 3 -
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_gem.c | 5 +
drivers/gpu/drm/rockchip/rockchip_drm_gem.h | 3 -
drivers/gpu/drm/tegra/gem.c | 5 +
drivers/gpu/drm/tegra/gem.h | 3 -
drivers/gpu/drm/udl/udl_drv.h | 3 -
drivers/gpu/drm/udl/udl_gem.c | 5 +
drivers/gpu/drm/vc4/vc4_bo.c | 5 +
drivers/gpu/drm/vc4/vc4_drv.h | 3 -
drivers/gpu/drm/vgem/vgem_drv.c | 7 +
drivers/gpu/drm/virtio/virtgpu_drv.h | 3 -
drivers/gpu/drm/virtio/virtgpu_ttm.c | 3 -
drivers/gpu/drm/vmwgfx/vmwgfx_drv.h | 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/v4l2-core/v4l2-dev.c | 3 -
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/comedi/comedi_fops.c | 3 -
.../staging/lustre/lustre/llite/llite_internal.h | 3 -
drivers/staging/lustre/lustre/llite/llite_mmap.c | 5 +
drivers/staging/vboxvideo/vbox_drv.h | 3 -
drivers/staging/vboxvideo/vbox_ttm.c | 3 -
drivers/staging/vme/devices/vme_user.c | 3 -
drivers/uio/uio.c | 3 -
drivers/usb/core/devio.c | 3 -
drivers/usb/mon/mon_bin.c | 3 -
drivers/vfio/vfio.c | 7 +
drivers/video/fbdev/core/fbmem.c | 3 -
drivers/video/fbdev/pxa3xx-gcu.c | 3 -
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/attr.c | 10 ++
fs/btrfs/file.c | 3 -
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/fcntl.c | 15 +++
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/open.c | 6 +
fs/orangefs/file.c | 5 +
fs/proc/inode.c | 7 +
fs/proc/vmcore.c | 6 +
fs/ramfs/file-nommu.c | 6 +
fs/read_write.c | 3 +
fs/romfs/mmap-nommu.c | 3 -
fs/ubifs/file.c | 5 +
fs/xfs/libxfs/xfs_bmap.c | 5 +
fs/xfs/xfs_bmap_util.c | 3 +
fs/xfs/xfs_file.c | 114 +++++++++++++++++++-
fs/xfs/xfs_inode.h | 1
fs/xfs/xfs_ioctl.c | 6 +
fs/xfs/xfs_super.c | 1
include/drm/drm_gem.h | 3 -
include/drm/drm_gem_cma_helper.h | 3 -
include/drm/drm_legacy.h | 3 -
include/linux/fs.h | 21 ++--
include/linux/mm.h | 2
include/linux/mman.h | 46 ++++++++
include/linux/syscalls.h | 3 +
include/misc/cxl.h | 3 -
include/uapi/asm-generic/mman.h | 1
include/uapi/linux/fcntl.h | 5 +
ipc/shm.c | 5 +
kernel/events/core.c | 3 -
kernel/kcov.c | 3 -
kernel/relay.c | 3 -
mm/filemap.c | 19 ++-
mm/mmap.c | 56 +++++++++-
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 -
virt/kvm/kvm_main.c | 3 -
177 files changed, 689 insertions(+), 234 deletions(-)