He, Qing wrote:
>
> When local apic timer is inactive or is expired in oneshot mode, it
> should not be restarted in save/restore or hrtimer migration. This
> patch fixes this.
>
> diff --git a/drivers/kvm/irq.h b/drivers/kvm/irq.h
> index 5f97e25..68d454c 100644
> --- a/drivers/kvm/irq.h
> +++ b/drivers/kvm/irq.h
> @@ -110,6 +110,7 @@ struct kvm_lapic {
> struct kvm_io_device dev;
> struct {
> atomic_t pending;
> + atomic_t active;
>
This is atomic, but you never use read-modify-write instructions (read
and write are atomic on a simple int).
> +
> + if (atomic_read(&apic->timer.active))
>
What if the timer fires here?
> + apic_set_reg(apic, APIC_TMCCT, tmict);
> + else
> + apic_set_reg(apic, APIC_TMCCT, 0);
> +}
> +
> void kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
> @@ -1036,11 +1062,14 @@ void kvm_migrate_apic_timer(struct kvm_vcpu
> *vcpu)
> struct kvm_lapic *apic = vcpu->apic;
> struct hrtimer *timer;
>
> - if (apic) {
> - timer = &apic->timer.dev;
> - hrtimer_cancel(timer);
> - hrtimer_start(timer, timer->expires, HRTIMER_MODE_ABS);
> - }
> + if (!apic)
> + return;
> +
> + timer = &apic->timer.dev;
> + hrtimer_cancel(timer);
> + if (atomic_read(&apic->timer.active))
>
Or here?
> + hrtimer_start(timer, timer->expires,
> + HRTIMER_MODE_ABS);
> }
> EXPORT_SYMBOL_GPL(kvm_migrate_apic_timer);
>
>
--
Any sufficiently difficult bug is indistinguishable from a feature.
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