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    SubjectRe: nmi_watchdog=2 regression in 2.6.21
    Hello,

    Here is a patch to fix the NMI watchdog problem on CoreDuo processor.
    I think we still need Daniel's patch to make the error path (when you
    are stuck) do the right cleanup.


    Changelog:
    - fix the NMI watchdog on Intel CoreDuo processor whereby the
    kernel would get stuck during boot. The issue is related to
    errata AE49, where the PERFEVTSEL1 counter does not have a
    working enable bit. Thus it is not possible to use it for NMI.
    The patch creates a dedicated wd_ops for CoreDuo which falls
    back to using PERFEVTSEL0. The other Intel processors supporting
    the architectural PMU will keep on using PERFEVTSEL1 as this
    allows other subsystems, such as perfmon, to use PERFEVTSEL0 for
    PEBS monitoring in particular.
    Bug initially reported by Daniel Walker.

    Signed-off-by: Stephane Eranian <eranian@hpl.hp.com>


    diff --git a/arch/i386/kernel/cpu/perfctr-watchdog.c b/arch/i386/kernel/cpu/perfctr-watchdog.c
    index 9b5d6af..f9066e1 100644
    --- a/arch/i386/kernel/cpu/perfctr-watchdog.c
    +++ b/arch/i386/kernel/cpu/perfctr-watchdog.c
    @@ -271,8 +271,8 @@ static int setup_k7_watchdog(unsigned nmi_hz)
    unsigned int evntsel;
    struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

    - perfctr_msr = MSR_K7_PERFCTR0;
    - evntsel_msr = MSR_K7_EVNTSEL0;
    + perfctr_msr = wd_ops->perfctr;
    + evntsel_msr = wd_ops->evntsel;

    wrmsrl(perfctr_msr, 0UL);

    @@ -351,8 +351,8 @@ static int setup_p6_watchdog(unsigned nmi_hz)
    unsigned int evntsel;
    struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

    - perfctr_msr = MSR_P6_PERFCTR0;
    - evntsel_msr = MSR_P6_EVNTSEL0;
    + perfctr_msr = wd_ops->perfctr;
    + evntsel_msr = wd_ops->evntsel;

    /* KVM doesn't implement this MSR */
    if (wrmsr_safe(perfctr_msr, 0, 0) < 0)
    @@ -577,8 +577,8 @@ static int setup_intel_arch_watchdog(unsigned nmi_hz)
    (ebx & ARCH_PERFMON_UNHALTED_CORE_CYCLES_PRESENT))
    return 0;

    - perfctr_msr = MSR_ARCH_PERFMON_PERFCTR1;
    - evntsel_msr = MSR_ARCH_PERFMON_EVENTSEL1;
    + perfctr_msr = wd_ops->perfctr;
    + evntsel_msr = wd_ops->evntsel;

    wrmsrl(perfctr_msr, 0UL);

    @@ -613,6 +613,16 @@ static struct wd_ops intel_arch_wd_ops = {
    .evntsel = MSR_ARCH_PERFMON_EVENTSEL1,
    };

    +static struct wd_ops coreduo_wd_ops = {
    + .reserve = single_msr_reserve,
    + .unreserve = single_msr_unreserve,
    + .setup = setup_intel_arch_watchdog,
    + .rearm = p6_rearm,
    + .stop = single_msr_stop_watchdog,
    + .perfctr = MSR_ARCH_PERFMON_PERFCTR0,
    + .evntsel = MSR_ARCH_PERFMON_EVENTSEL0,
    +};
    +
    static void probe_nmi_watchdog(void)
    {
    switch (boot_cpu_data.x86_vendor) {
    @@ -623,6 +633,10 @@ static void probe_nmi_watchdog(void)
    wd_ops = &k7_wd_ops;
    break;
    case X86_VENDOR_INTEL:
    + if (boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model == 14) {
    + wd_ops = &coreduo_wd_ops;
    + break;
    + }
    if (cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
    wd_ops = &intel_arch_wd_ops;
    break;
    -
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