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    Subject[patch 31/66] x86/kvm/kvmclock: Convert to hotplug state machine
    From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

    Install the callbacks via the state machine and let the core invoke
    the callbacks on the already online CPUs.

    We assumed that the priority ordering was ment to invoke the online
    callback as the last step. In the original code this also invoked the
    down prepare callback as the last step. With the symmetric state
    machine the down prepare callback is now the first step.

    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Cc: Gleb Natapov <gleb@kernel.org>
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Cc: kvm@vger.kernel.org
    Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
    ---
    arch/x86/kvm/x86.c | 35 ++++++++---------------------------
    include/linux/cpuhotplug.h | 1 +
    2 files changed, 9 insertions(+), 27 deletions(-)

    --- a/arch/x86/kvm/x86.c
    +++ b/arch/x86/kvm/x86.c
    @@ -5552,9 +5552,10 @@ int kvm_fast_pio_out(struct kvm_vcpu *vc
    }
    EXPORT_SYMBOL_GPL(kvm_fast_pio_out);

    -static void tsc_bad(void *info)
    +static int kvmclock_cpu_down_prep(unsigned int cpu)
    {
    __this_cpu_write(cpu_tsc_khz, 0);
    + return 0;
    }

    static void tsc_khz_changed(void *data)
    @@ -5659,35 +5660,18 @@ static struct notifier_block kvmclock_cp
    .notifier_call = kvmclock_cpufreq_notifier
    };

    -static int kvmclock_cpu_notifier(struct notifier_block *nfb,
    - unsigned long action, void *hcpu)
    +static int kvmclock_cpu_online(unsigned int cpu)
    {
    - unsigned int cpu = (unsigned long)hcpu;
    -
    - switch (action) {
    - case CPU_ONLINE:
    - case CPU_DOWN_FAILED:
    - tsc_khz_changed(NULL);
    - break;
    - case CPU_DOWN_PREPARE:
    - tsc_bad(NULL);
    - break;
    - }
    - return NOTIFY_OK;
    + tsc_khz_changed(NULL);
    + return 0;
    }

    -static struct notifier_block kvmclock_cpu_notifier_block = {
    - .notifier_call = kvmclock_cpu_notifier,
    - .priority = -INT_MAX
    -};
    -
    static void kvm_timer_init(void)
    {
    int cpu;

    max_tsc_khz = tsc_khz;

    - cpu_notifier_register_begin();
    if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
    #ifdef CONFIG_CPU_FREQ
    struct cpufreq_policy policy;
    @@ -5702,12 +5686,9 @@ static void kvm_timer_init(void)
    CPUFREQ_TRANSITION_NOTIFIER);
    }
    pr_debug("kvm: max_tsc_khz = %ld\n", max_tsc_khz);
    - for_each_online_cpu(cpu)
    - smp_call_function_single(cpu, tsc_khz_changed, NULL, 1);
    -
    - __register_hotcpu_notifier(&kvmclock_cpu_notifier_block);
    - cpu_notifier_register_done();

    + cpuhp_setup_state(CPUHP_AP_X86_KVM_CLK_ONLINE, "AP_X86_KVM_CLK_ONLINE",
    + kvmclock_cpu_online, kvmclock_cpu_down_prep);
    }

    static DEFINE_PER_CPU(struct kvm_vcpu *, current_vcpu);
    @@ -5896,7 +5877,7 @@ void kvm_arch_exit(void)
    if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
    cpufreq_unregister_notifier(&kvmclock_cpufreq_notifier_block,
    CPUFREQ_TRANSITION_NOTIFIER);
    - unregister_hotcpu_notifier(&kvmclock_cpu_notifier_block);
    + cpuhp_remove_state_nocalls(CPUHP_X86_KVM_CLK_ONLINE);
    #ifdef CONFIG_X86_64
    pvclock_gtod_unregister_notifier(&pvclock_gtod_notifier);
    #endif
    --- a/include/linux/cpuhotplug.h
    +++ b/include/linux/cpuhotplug.h
    @@ -56,6 +56,7 @@ enum cpuhp_state {
    CPUHP_AP_ONLINE_DYN,
    CPUHP_AP_ONLINE_DYN_END = CPUHP_AP_ONLINE_DYN + 30,
    CPUHP_AP_X86_HPET_ONLINE,
    + CPUHP_AP_X86_KVM_CLK_ONLINE,
    CPUHP_AP_ACTIVE,
    CPUHP_ONLINE,
    };

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