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    SubjectRe: new text patching for review
    * Zachary Amsden (zach@vmware.com) wrote:
    > Mathieu Desnoyers wrote:
    > >Yes, kprobes is case 1: atomic update. And we don't even have to bother
    > >about Intel's erratum. This one is ok. That's mainly the
    > >alternatives/paravirt code I worry about.
    > >
    >
    > Paravirt and alternatives should all be ok because they are done before
    > SMP bringup and with NMIs disabled. NMI watchdog is not setup until
    > smp_prepare_cpus/check_nmi_watchdog, which happens way later, not during
    > parse_args/setup_nmi_watchdog, which just decides which type of watchdog
    > to setup.
    >

    I'm not so sure about this. You are right in that it has nothing to do
    with parse_args, but I just went in detail through the source, and the
    order seems to be:

    1 - NMI is activated
    2 - MCE is activated
    3 - alternatives are applied

    In detail:

    start_kernel()
    ...
    include/asm-i386/smp.h:smp_prepare_boot_cpu()
    smp_ops.smp_prepare_boot_cpu()
    arch/i386/kernel/smpboot.c:native_smp_prepare_boot_cpu()
    arch/i386/kernel/smpboot.c:native_smp_prepare_cpus()
    arch/i386/kernel/smpboot.c:smp_boot_cpus()
    arch/i386/kernel/apic.c:setup_local_APIC()
    arch/i386/kernel/nmi.c:setup_apic_nmi_watchdog()
    arch/i386/kernel/cpu/perfctr-watchdog.c:lapic_watchdog_init()
    wd_ops->setup() (e.g. setup_intel_arch_watchdog)
    ...
    arch/i386/kernel/cpu/bugs.c:check_bugs()
    arch/i386/kernel/cpu/common.c:identify_boot_cpu()
    identify_cpu()
    arch/i386/kernel/cpu/mcheck/mce.c:mcheck_init()
    arch/i386/kernel/cpu/mcheck/p4.c:intel_p4_mcheck_init()
    ...
    arch/i386/kernel/alternative_instructions()
    ...

    Therefore, applying alternatives instructions seems to be done after NMI
    and MCE init at boot time, or am I misunderstanding something ?


    > I originally considered the NMI problem for paravirt-ops patching done
    > during module load, and found that I would need to modify
    > stop_machine_run to have an architecture specific callout to mask and
    > unmask NMIs. I didn't imagine that would be very popular, and VMI was
    > the only paravirt-ops that were considering module load time patching,
    > so I flushed it.
    >
    > You get some other nasty issues as well with run-time switching, like
    > missing early init calls (in particular, we would have to go to some
    > heroics to retake the land surrounding the APIC local timer interrupt).
    >
    > Zach

    --
    Mathieu Desnoyers
    Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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