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    Subject[tip:smp/hotplug] arm/xen: Convert to hotplug state machine
    Commit-ID:  4761adb6f49048cddd65553a71ea2354b2a838be
    Gitweb: http://git.kernel.org/tip/4761adb6f49048cddd65553a71ea2354b2a838be
    Author: Richard Cochran <rcochran@linutronix.de>
    AuthorDate: Wed, 13 Jul 2016 17:16:52 +0000
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Fri, 15 Jul 2016 10:40:28 +0200

    arm/xen: Convert to hotplug state machine

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

    The get_cpu() in xen_starting_cpu() boils down to preempt_disable() since
    we already know the CPU we run on. Disabling preemption shouldn't be required
    here from what I see since it we don't switch CPUs while invoking the function.

    Signed-off-by: Richard Cochran <rcochran@linutronix.de>
    Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
    Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Russell King <linux@armlinux.org.uk>
    Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: linux-arm-kernel@lists.infradead.org
    Cc: rt@linutronix.de
    Cc: xen-devel@lists.xenproject.org
    Link: http://lkml.kernel.org/r/20160713153336.971559670@linutronix.de
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/arm/xen/enlighten.c | 41 +++++++++++------------------------------
    include/linux/cpuhotplug.h | 1 +
    2 files changed, 12 insertions(+), 30 deletions(-)

    diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
    index 75cd734..d822e23 100644
    --- a/arch/arm/xen/enlighten.c
    +++ b/arch/arm/xen/enlighten.c
    @@ -161,12 +161,11 @@ static struct notifier_block xen_pvclock_gtod_notifier = {
    .notifier_call = xen_pvclock_gtod_notify,
    };

    -static void xen_percpu_init(void)
    +static int xen_starting_cpu(unsigned int cpu)
    {
    struct vcpu_register_vcpu_info info;
    struct vcpu_info *vcpup;
    int err;
    - int cpu = get_cpu();

    /*
    * VCPUOP_register_vcpu_info cannot be called twice for the same
    @@ -190,7 +189,13 @@ static void xen_percpu_init(void)

    after_register_vcpu_info:
    enable_percpu_irq(xen_events_irq, 0);
    - put_cpu();
    + return 0;
    +}
    +
    +static int xen_dying_cpu(unsigned int cpu)
    +{
    + disable_percpu_irq(xen_events_irq);
    + return 0;
    }

    static void xen_restart(enum reboot_mode reboot_mode, const char *cmd)
    @@ -209,28 +214,6 @@ static void xen_power_off(void)
    BUG_ON(rc);
    }

    -static int xen_cpu_notification(struct notifier_block *self,
    - unsigned long action,
    - void *hcpu)
    -{
    - switch (action) {
    - case CPU_STARTING:
    - xen_percpu_init();
    - break;
    - case CPU_DYING:
    - disable_percpu_irq(xen_events_irq);
    - break;
    - default:
    - break;
    - }
    -
    - return NOTIFY_OK;
    -}
    -
    -static struct notifier_block xen_cpu_notifier = {
    - .notifier_call = xen_cpu_notification,
    -};
    -
    static irqreturn_t xen_arm_callback(int irq, void *arg)
    {
    xen_hvm_evtchn_do_upcall();
    @@ -351,16 +334,14 @@ static int __init xen_guest_init(void)
    return -EINVAL;
    }

    - xen_percpu_init();
    -
    - register_cpu_notifier(&xen_cpu_notifier);
    -
    pv_time_ops.steal_clock = xen_stolen_accounting;
    static_key_slow_inc(&paravirt_steal_enabled);
    if (xen_initial_domain())
    pvclock_gtod_register_notifier(&xen_pvclock_gtod_notifier);

    - return 0;
    + return cpuhp_setup_state(CPUHP_AP_ARM_XEN_STARTING,
    + "AP_ARM_XEN_STARTING", xen_starting_cpu,
    + xen_dying_cpu);
    }
    early_initcall(xen_guest_init);

    diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
    index ad48881..4c02b52 100644
    --- a/include/linux/cpuhotplug.h
    +++ b/include/linux/cpuhotplug.h
    @@ -47,6 +47,7 @@ enum cpuhp_state {
    CPUHP_AP_KVM_STARTING,
    CPUHP_AP_KVM_ARM_VGIC_STARTING,
    CPUHP_AP_KVM_ARM_TIMER_STARTING,
    + CPUHP_AP_ARM_XEN_STARTING,
    CPUHP_AP_LEDTRIG_STARTING,
    CPUHP_AP_NOTIFY_STARTING,
    CPUHP_AP_ONLINE,
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