Avi Kivity wrote:
> 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);
>>
>>
>
I think you could use the return value of hrtimer_cancel() here:
if (hrtimer_cancel(...))
hrtimer_start(...);
--
Any sufficiently difficult bug is indistinguishable from a feature.
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