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    Subject[PATCH] Fix triplefault on x86-64 bootup
    Hello,
    after I upgraded kernel on my box to current git, only thing it did
    was rebooting in a loop. After some digging I found that it is silly
    to apply alternative to memcpy by using that every same memcpy...
    Sorry if it is known bug, I do not see it reported in my LKML mailbox...
    Petr

    From: Petr Vandrovec <petr@vandrovec.name>

    Do not replace whole memcpy in apply alternatives

    apply_alternatives uses memcpy() to apply alternatives. Which has
    unfortunate effect that while applying memcpy alternative memcpy itself
    it tries to overwrite itself with nops - which causes #UD fault as it
    overwrites half of instruction in copy loop, and from this point on only
    possible outcome is triplefault and reboot. So let's overwrite only
    first two instructions of memcpy - as long as main memcpy loop is
    not in first two bytes it will work fine.

    Signed-off-by: Petr Vandrovec <petr@vandrovec.name>

    ---
    commit 7c6f7d582f301e16899a43fd6c775ed103e8a8d2
    tree 112d7320e8a21120e4e43f1ac91918ca0352ff56
    parent f81e9b8cc6301f6328eafaa553ef35441874b1a4
    author Petr Vandrovec <petr@vandrovec.name> Sun, 12 Aug 2007 01:05:11 -0700
    committer Petr Vandrovec <petr@vandrovec.name> Sun, 12 Aug 2007 01:05:11 -0700

    arch/x86_64/lib/memcpy.S | 4 +++-
    1 files changed, 3 insertions(+), 1 deletions(-)

    diff --git a/arch/x86_64/lib/memcpy.S b/arch/x86_64/lib/memcpy.S
    index 0ea0ddc..c22981f 100644
    --- a/arch/x86_64/lib/memcpy.S
    +++ b/arch/x86_64/lib/memcpy.S
    @@ -124,6 +124,8 @@ ENDPROC(__memcpy)
    .quad memcpy
    .quad 1b
    .byte X86_FEATURE_REP_GOOD
    - .byte .Lfinal - memcpy
    + /* Replace only beginning, memcpy is used to apply alternatives, so it
    + * is silly to overwrite itself with nops - reboot is only outcome... */
    + .byte 2b - 1b
    .byte 2b - 1b
    .previous
    -
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