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    Subject[PATCH v8 0/3] Machine check recovery when kernel accesses poison
    This series is initially targeted at the folks doing filesystems
    on top of NVDIMMs. They really want to be able to return -EIO
    when there is a h/w error (just like spinning rust, and SSD does).

    I plan to use the same infrastructure to write a machine check aware
    "copy_from_user()" that will SIGBUS the calling application when a
    syscall touches poison in user space (just like we do when the application
    touches the poison itself).

    Changes V7-V8
    Boris: Would be so much cleaner if we added a new field to the exception table
    instead of squeezing bits into the fixup field. New field added
    Tony: Documentation needs to be updated. Done

    Changes V6-V7:
    Boris: Why add/subtract 0x20000000? Added better comment provided by Andy
    Boris: Churn. Part2 changes things only introduced in part1.
    Merged parts 1&2 into one patch.
    Ingo: Missing my sign off on part1. Added.

    Changes V5-V6
    Andy: Provoked massive re-write by providing what is now part1 of this
    patch series. This frees up two bits in the exception table
    fixup field that can be used to tag exception table entries
    as different "classes". This means we don't need my separate
    exception table fro machine checks. Also avoids duplicating
    fixup actions for #PF and #MC cases that were in version 5.
    Andy: Use C99 array initializers to tie the various class fixup
    functions back to the defintions of each class. Also give the
    functions meanningful names (not fixup_class0() etc.).
    Boris: Cleaned up my lousy assembly code removing many spurious 'l'
    modifiers on instructions.
    Boris: Provided some helper functions for the machine check severity
    calculation that make the code more readable.
    Boris: Have __mcsafe_copy() return a structure with the 'remaining bytes'
    in a separate field from the fault indicator. Boris had suggested
    Linux -EFAULT/-EINVAL ... but I thought it made more sense to return
    the exception number (X86_TRAP_MC, etc.) This finally kills off
    BIT(63) which has been controversial throughout all the early versions
    of this patch series.

    Changes V4-V5
    Tony: Extended __mcsafe_copy() to have fixup entries for both machine
    check and page fault.

    Changes V3-V4:
    Andy: Simplify fixup_mcexception() by dropping used-once local variable
    Andy: "Reviewed-by" tag added to part1
    Boris: Moved new functions to memcpy_64.S and declaration to asm/string_64.h
    Boris: Changed name s/mcsafe_memcpy/__mcsafe_copy/ to make it clear that this
    is an internal function and that return value doesn't follow memcpy() semantics.
    Boris: "Reviewed-by" tag added to parts 1&2

    Changes V2-V3:

    Andy: Don't hack "regs->ax = BIT(63) | addr;" in the machine check
    handler. Now have better fixup code that computes the number
    of remaining bytes (just like page-fault fixup).
    Andy: #define for BIT(63). Done, plus couple of extra macros using it.
    Boris: Don't clutter up generic code (like mm/extable.c) with this.
    I moved everything under arch/x86 (the asm-generic change is
    a more generic #define).
    Boris: Dependencies for CONFIG_MCE_KERNEL_RECOVERY are too generic.
    I made it a real menu item with default "n". Dan Williams
    will use "select MCE_KERNEL_RECOVERY" from his persistent
    filesystem code.
    Boris: Simplify conditionals in mce.c by moving tolerant/kill_it
    checks earlier, with a skip to end if they aren't set.
    Boris: Miscellaneous grammar/punctuation. Fixed.
    Boris: Don't leak spurious __start_mcextable symbols into kernels
    that didn't configure MCE_KERNEL_RECOVERY. Done.
    Tony: New code doesn't belong in user_copy_64.S/uaccess*.h. Moved
    to new .S/.h files
    Elliott:Cacheing behavior non-optimal. Could use movntdqa, vmovntdqa
    or vmovntdqa on source addresses. I didn't fix this yet. Think
    of the current mcsafe_memcpy() as the first of several functions.
    This one is useful for small copies (meta-data) where the overhead
    of saving SSE/AVX state isn't justified.

    Changes V1->V2:

    0-day: Reported build errors and warnings on 32-bit systems. Fixed
    0-day: Reported bloat to tinyconfig. Fixed
    Boris: Suggestions to use extra macros to reduce code duplication in _ASM_*EXTABLE. Done
    Boris: Re-write "tolerant==3" check to reduce indentation level. See below.
    Andy: Check IP is valid before searching kernel exception tables. Done.
    Andy: Explain use of BIT(63) on return value from mcsafe_memcpy(). Done (added decode macros).
    Andy: Untangle mess of code in tail of do_machine_check() to make it
    clear what is going on (e.g. that we only enter the ist_begin_non_atomic()
    if we were called from user code, not from kernel!). Done.
    Tony Luck (3):
    x86: Expand exception table to allow new handling options
    x86, mce: Check for faults tagged in EXTABLE_CLASS_FAULT exception
    table entries
    x86, mce: Add __mcsafe_copy()

    Documentation/x86/exception-tables.txt | 34 ++++++++
    arch/x86/include/asm/asm.h | 44 ++++++----
    arch/x86/include/asm/string_64.h | 8 ++
    arch/x86/include/asm/uaccess.h | 13 +--
    arch/x86/kernel/cpu/mcheck/mce-severity.c | 32 ++++++-
    arch/x86/kernel/cpu/mcheck/mce.c | 71 ++++++++--------
    arch/x86/kernel/kprobes/core.c | 2 +-
    arch/x86/kernel/traps.c | 6 +-
    arch/x86/kernel/x8664_ksyms_64.c | 2 +
    arch/x86/lib/memcpy_64.S | 133 ++++++++++++++++++++++++++++++
    arch/x86/mm/extable.c | 84 ++++++++++++-------
    arch/x86/mm/fault.c | 2 +-
    scripts/sortextable.c | 30 +++++++
    13 files changed, 370 insertions(+), 91 deletions(-)

    --
    2.1.4

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