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    SubjectRe: [PATCH -tip v5 07/10] kprobes/x86: Support kprobes jump optimization on x86
    Hi Peter,

    H. Peter Anvin wrote:
    > On 11/23/2009 03:22 PM, Masami Hiramatsu wrote:
    >> This uses stop_machine() for corss modifying code from int3 to jump.
    >> It doesn't allow us to modify code on NMI/SMI path. However, since
    >> kprobes itself doesn't support NMI/SMI code probing, it's not a
    >> problem.
    > I'm a bit confused by the above statement... does that mean you're
    > poking int3 and *then* do stop_machine()?

    Yes, as I said in,
    there are two separated issues.

    We have to separate below issues:
    - int3-based multi-bytes code replacement
    - multi-instruction replacement with int3-detour code

    The former is implemented on patch 9/10 and 10/10. As you can see,
    these patches are RFC status, because I'd like to wait for official
    reply of safeness from processor architects.
    And it may be able to use a dummy IPI for 2nd IPI because it
    just for waiting int3 interrupts. But again, it is just estimated that
    replacing with/recovering from int3 is automatically synchronized...

    However, at least stop_machine() method is officially described
    at "7.1.3 Handling Self- and Cross-Modifying Code" on the intel's
    software developer's manual 3A . So currently we can use it.

    For the latter issue, as I explained on previous reply, we need
    to wait all running interrupts including hardware interrupts.
    Thus I used synchronize_sched().

    So that the previous "x86 generic jump patching" patch is
    basically for single-instruction replacement. For multi-instructions
    replacement, we need to make detour code and wait for all running
    interruption. (of course, there are other static code limitations,
    as I described at "Safety check" section in patch 0/10.)

    Thank you,

    Masami Hiramatsu

    Software Engineer
    Hitachi Computer Products (America), Inc.
    Software Solutions Division


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