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    Subject[PATCH v2 0/9] use memcpy_mcsafe() for copy_to_iter()
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    Date
    Changes since v1 [1]:

    * Remove the loop unrolling in the assembly implementation since it
    significantly complicates the exception handling (Linus)

    * Introduce a ->copy_to_iter() dax operation for symmetry with the
    existing ->copy_from_iter() operation to allow platform /
    device-specific implementations.

    [1]: https://lists.01.org/pipermail/linux-nvdimm/2018-May/015548.html

    ---

    Currently memcpy_mcsafe() is only deployed in the pmem driver when
    reading through a /dev/pmemX block device. However, a filesystem in dax
    mode mounted on a /dev/pmemX block device will bypass the block layer
    and the driver for reads. The filesystem-dax (fsdax) read case uses
    dax_direct_access() and copy_to_iter() to bypass the block layer.

    The result of the bypass is that the kernel treats machine checks during
    read as system fatal (reboot) when they could simply be flagged as an
    I/O error, similar to performing reads through the pmem driver. Prevent
    this fatal condition by deploying memcpy_mcsafe() in the fsdax read
    path.

    The main differences between this copy_to_user_mcsafe() and
    copy_user_generic_unrolled() are:

    * Typical tail/residue handling after a fault retries the copy
    byte-by-byte until the fault happens again. Re-triggering machine
    checks is potentially fatal so the implementation uses source alignment
    and poison alignment assumptions to avoid re-triggering machine
    checks.

    * SMAP coordination is handled external to the assembly with
    __uaccess_begin() and __uaccess_end().

    * ITER_KVEC and ITER_BVEC can now end prematurely with an error.

    The new MCSAFE_DEBUG facility is proposed as a way to unit test the
    exception handling without requiring an ACPI EINJ capable platform.

    ---

    Dan Williams (9):
    x86, memcpy_mcsafe: remove loop unrolling
    x86, memcpy_mcsafe: add labels for write fault handling
    x86, memcpy_mcsafe: return bytes remaining
    x86, memcpy_mcsafe: add write-protection-fault handling
    x86, memcpy_mcsafe: define copy_to_iter_mcsafe()
    dax: introduce a ->copy_to_iter dax operation
    dax: report bytes remaining in dax_iomap_actor()
    pmem: switch to copy_to_iter_mcsafe()
    x86, nfit_test: unit test for memcpy_mcsafe()


    arch/x86/Kconfig | 1
    arch/x86/Kconfig.debug | 3 +
    arch/x86/include/asm/mcsafe_debug.h | 50 ++++++++++++++++
    arch/x86/include/asm/string_64.h | 10 ++-
    arch/x86/include/asm/uaccess_64.h | 14 ++++
    arch/x86/lib/memcpy_64.S | 109 ++++++++++++++++-------------------
    arch/x86/lib/usercopy_64.c | 17 +++++
    drivers/dax/super.c | 10 +++
    drivers/md/dm-linear.c | 16 +++++
    drivers/md/dm-log-writes.c | 15 +++++
    drivers/md/dm-stripe.c | 21 +++++++
    drivers/md/dm.c | 25 ++++++++
    drivers/nvdimm/claim.c | 3 +
    drivers/nvdimm/pmem.c | 13 +++-
    drivers/s390/block/dcssblk.c | 7 ++
    fs/dax.c | 21 ++++---
    include/linux/dax.h | 5 ++
    include/linux/device-mapper.h | 5 +-
    include/linux/string.h | 4 +
    include/linux/uio.h | 15 +++++
    lib/iov_iter.c | 61 ++++++++++++++++++++
    tools/testing/nvdimm/test/nfit.c | 48 +++++++++++++++
    22 files changed, 394 insertions(+), 79 deletions(-)
    create mode 100644 arch/x86/include/asm/mcsafe_debug.h

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