On 09/06/2016 11:31, Alan Jenkins wrote:
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 1a2da0e..84abb1a 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1273,7 +1273,6 @@ static void apic_timer_expired(struct kvm_lapic *apic)
> {
> struct kvm_vcpu *vcpu = apic->vcpu;
> struct swait_queue_head *q = &vcpu->wq;
> - struct kvm_timer *ktimer = &apic->lapic_timer;
>
> if (atomic_read(&apic->lapic_timer.pending))
> return;
> @@ -1283,9 +1282,6 @@ static void apic_timer_expired(struct kvm_lapic *apic)
>
> if (swait_active(q))
> swake_up(q);
> -
> - if (apic_lvtt_tscdeadline(apic))
> - ktimer->expired_tscdeadline = ktimer->tscdeadline;
> }
>
> /*
> @@ -1922,12 +1918,15 @@ int kvm_apic_accept_pic_intr(struct kvm_vcpu *vcpu)
> void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu)
> {
> struct kvm_lapic *apic = vcpu->arch.apic;
> + struct kvm_timer *ktimer = &apic->lapic_timer;
>
> - if (atomic_read(&apic->lapic_timer.pending) > 0) {
> + if (atomic_read(&ktimer->pending) > 0) {
> kvm_apic_local_deliver(apic, APIC_LVTT);
> - if (apic_lvtt_tscdeadline(apic))
> - apic->lapic_timer.tscdeadline = 0;
> - atomic_set(&apic->lapic_timer.pending, 0);
> + if (apic_lvtt_tscdeadline(apic)) {
> + ktimer->expired_tscdeadline = ktimer->tscdeadline;
> + ktimer->tscdeadline = 0;
> + }
> + atomic_set(&ktimer->pending, 0);
> }
> }
>
> @@ -2007,6 +2006,71 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
> }
>
> /*
> + * kvm_apic_tsc_update - called when guest or host changes the TSC
> + *
> + * Update the emulated TSC deadline timer.
> + *
> + * It is also required if host changes TSC frequency scaling. It is not
> + * required when we "catch up" the TSC, because that is maintaining the
> + * relationship between TSC and real time.
> + */
> +void kvm_apic_tsc_update(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_lapic *apic = vcpu->arch.apic;
> + struct kvm_timer *ktimer = &apic->lapic_timer;
> +
> + if (!lapic_in_kernel(vcpu))
> + return;
> +
> + if (!apic_lvtt_tscdeadline(apic))
> + return;
> +
> + hrtimer_cancel(&ktimer->timer);
> +
> + /*
> + * Handle when guest TSC is adjusted backwards, just after
> + * inject_apic_timer_irqs(). When we hit wait_lapic_expire(), we risk
> + * an extended busy-wait. Because ktimer->expired_tscdeadline will
> + * have receded further into the future.
> + *
> + * The guest does not get a chance to run in this window, but the host
> + * could modify the TSC at this point. This race could happen when
> + * restoring a live snapshot of a VM.
> + *
> + * Just clear the busy-wait. In theory this could cause a wakeup
> + * before the deadline, if the user configured the the busy-wait
> + * feature (lapic_advance_timer_ns). We don't expect this to matter:
Why not just delay by lapic_advance_timer_ns here? It's usually around
10 nanoseconds, it should be cheap.
Paolo
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