Changes since v3 [1]: * Kill the i_daxdma_lock, and do not impose any new locking constraints on filesystem implementations (Dave) * Reuse the existing i_mmap_lock for synchronizing against get_user_pages() by unmapping and causing punch-hole/truncate to re-fault the page before get_user_pages() can elevate the page reference count (Jan) * Create a dax-specifc address_space_operations instance for each filesystem. This allows page->mapping to be set for dax pages. (Jan). * Change the ext4 and ext2 policy of 'mount -o dax' vs a device that does not support dax. This converts any environments that may have been using 'page-less' dax back to using page cache. * Rename wait_on_devmap_idle() to wait_on_atomic_one(), a generic facility for waiting for an atomic counter to reach a value of '1'. [1]: https://lwn.net/Articles/737273/ --- Background: get_user_pages() pins file backed memory pages for access by dma devices. However, it only pins the memory pages not the page-to-file offset association. If a file is truncated the pages are mapped out of the file and dma may continue indefinitely into a page that is owned by a device driver. This breaks coherency of the file vs dma, but the assumption is that if userspace wants the file-space truncated it does not matter what data is inbound from the device, it is not relevant anymore. The only expectation is that dma can safely continue while the filesystem reallocates the block(s). Problem: This expectation that dma can safely continue while the filesystem changes the block map is broken by dax. With dax the target dma page *is* the filesystem block. The model of leaving the page pinned for dma, but truncating the file block out of the file, means that the filesytem is free to reallocate a block under active dma to another file and now the expected data-incoherency situation has turned into active data-corruption. Solution: Defer all filesystem operations (fallocate(), truncate()) on a dax mode file while any page/block in the file is under active dma. This solution assumes that dma is transient. Cases where dma operations are known to not be transient, like RDMA, have been explicitly disabled via commits like 5f1d43de5416 "IB/core: disable memory registration of filesystem-dax vmas". The dax_flush_dma() routine is called by filesystems with a lock held against mm faults (i_mmap_lock). It then invalidates all mappings to trigger any subsequent get_user_pages() to block on i_mmap_lock. Finally it scans/rescans all pages in the mapping until it observes all pages idle. So far this solution only targets xfs since it already implements xfs_break_layouts in all the locations that would need this synchronization. It applies on top of the vmem_altmap / dev_pagemap reworks from Christoph. --- Dan Williams (18): mm, dax: introduce pfn_t_special() ext4: auto disable dax instead of failing mount ext2: auto disable dax instead of failing mount dax: require 'struct page' by default for filesystem dax dax: stop using VM_MIXEDMAP for dax dax: stop using VM_HUGEPAGE for dax dax: store pfns in the radix tools/testing/nvdimm: add 'bio_delay' mechanism mm, dax: enable filesystems to trigger dev_pagemap ->page_free callbacks mm, dev_pagemap: introduce CONFIG_DEV_PAGEMAP_OPS fs, dax: introduce DEFINE_FSDAX_AOPS xfs: use DEFINE_FSDAX_AOPS ext4: use DEFINE_FSDAX_AOPS ext2: use DEFINE_FSDAX_AOPS mm, fs, dax: use page->mapping to warn if dma collides with truncate wait_bit: introduce {wait_on,wake_up}_atomic_one mm, fs, dax: dax_flush_dma, handle dma vs block-map-change collisions xfs, dax: wire up dax_flush_dma support via a new xfs_sync_dma helper arch/powerpc/platforms/Kconfig | 1 arch/powerpc/sysdev/axonram.c | 2 drivers/dax/device.c | 1 drivers/dax/super.c | 100 ++++++++++- drivers/nvdimm/pmem.c | 3 drivers/s390/block/Kconfig | 1 drivers/s390/block/dcssblk.c | 3 fs/Kconfig | 8 + fs/dax.c | 295 ++++++++++++++++++++++++++++----- fs/ext2/ext2.h | 1 fs/ext2/file.c | 1 fs/ext2/inode.c | 23 ++- fs/ext2/namei.c | 18 -- fs/ext2/super.c | 13 + fs/ext4/file.c | 1 fs/ext4/inode.c | 6 + fs/ext4/super.c | 15 +- fs/xfs/Makefile | 3 fs/xfs/xfs_aops.c | 2 fs/xfs/xfs_aops.h | 1 fs/xfs/xfs_dma.c | 81 +++++++++ fs/xfs/xfs_dma.h | 24 +++ fs/xfs/xfs_file.c | 8 - fs/xfs/xfs_ioctl.c | 7 - fs/xfs/xfs_iops.c | 12 + fs/xfs/xfs_super.c | 20 +- include/linux/dax.h | 70 +++++++- include/linux/memremap.h | 28 +-- include/linux/mm.h | 62 +++++-- include/linux/pfn_t.h | 13 + include/linux/vma.h | 23 +++ include/linux/wait_bit.h | 13 + kernel/memremap.c | 30 +++ kernel/sched/wait_bit.c | 59 ++++++- mm/Kconfig | 5 + mm/gup.c | 5 + mm/hmm.c | 13 - mm/huge_memory.c | 6 - mm/ksm.c | 3 mm/madvise.c | 2 mm/memory.c | 22 ++ mm/migrate.c | 3 mm/mlock.c | 5 - mm/mmap.c | 8 - mm/swap.c | 3 tools/testing/nvdimm/Kbuild | 1 tools/testing/nvdimm/test/iomap.c | 62 +++++++ tools/testing/nvdimm/test/nfit.c | 34 ++++ tools/testing/nvdimm/test/nfit_test.h | 1 49 files changed, 918 insertions(+), 203 deletions(-) create mode 100644 fs/xfs/xfs_dma.c create mode 100644 fs/xfs/xfs_dma.h create mode 100644 include/linux/vma.h
