On 03/02/2016 17:23, Radim Krčmář wrote:
> Following patches would be even uglier if inject_lock didn't go away.
>
> Patch changes the virtual wire comment to better describe our situation.
>
> Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> ---
> arch/x86/kvm/i8254.c | 67 ++++++++++++++++++++++------------------------------
> arch/x86/kvm/i8254.h | 3 +--
> 2 files changed, 29 insertions(+), 41 deletions(-)
>
> diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
> index de5f5018026f..a137eb381012 100644
> --- a/arch/x86/kvm/i8254.c
> +++ b/arch/x86/kvm/i8254.c
> @@ -236,16 +236,13 @@ static void kvm_pit_ack_irq(struct kvm_irq_ack_notifier *kian)
> {
> struct kvm_kpit_state *ps = container_of(kian, struct kvm_kpit_state,
> irq_ack_notifier);
> - int value;
>
> - spin_lock(&ps->inject_lock);
> + atomic_set(&ps->irq_ack, 1);
smp_mb__before_atomic();
> if (atomic_add_unless(&ps->pending, -1, 0))
> /* in this case, we had multiple outstanding pit interrupts
> * that we needed to inject. Reinject
> */
> queue_kthread_work(&ps->pit->worker, &ps->pit->expired);
> - ps->irq_ack = 1;
> - spin_unlock(&ps->inject_lock);
> }
>
> void __kvm_migrate_pit_timer(struct kvm_vcpu *vcpu)
> @@ -276,34 +273,25 @@ static void pit_do_work(struct kthread_work *work)
> struct kvm_vcpu *vcpu;
> int i;
> struct kvm_kpit_state *ps = &pit->pit_state;
> - int inject = 0;
>
> - /* Try to inject pending interrupts when
> - * last one has been acked.
> + if (!atomic_xchg(&ps->irq_ack, 0))
> + return;
> +
> + kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1, false);
> + kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 0, false);
> +
> + /*
> + * Provides NMI watchdog support via Virtual Wire mode.
> + * The route is: PIT -> LVT0 in NMI mode.
> + *
> + * Note: Our Virtual Wire implementation does not follow
> + * the MP specification. We propagate a PIT interrupt to all
> + * VCPUs and only when LVT0 is in NMI mode. The interrupt can
> + * also be simultaneously delivered through PIC and IOAPIC.
> */
> - spin_lock(&ps->inject_lock);
> - if (ps->irq_ack) {
> - ps->irq_ack = 0;
> - inject = 1;
> - }
> - spin_unlock(&ps->inject_lock);
> - if (inject) {
> - kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1, false);
> - kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 0, false);
> -
> - /*
> - * Provides NMI watchdog support via Virtual Wire mode.
> - * The route is: PIT -> PIC -> LVT0 in NMI mode.
> - *
> - * Note: Our Virtual Wire implementation is simplified, only
> - * propagating PIT interrupts to all VCPUs when they have set
> - * LVT0 to NMI delivery. Other PIC interrupts are just sent to
> - * VCPU0, and only if its LVT0 is in EXTINT mode.
> - */
> - if (atomic_read(&kvm->arch.vapics_in_nmi_mode) > 0)
> - kvm_for_each_vcpu(i, vcpu, kvm)
> - kvm_apic_nmi_wd_deliver(vcpu);
> - }
> + if (atomic_read(&kvm->arch.vapics_in_nmi_mode) > 0)
> + kvm_for_each_vcpu(i, vcpu, kvm)
> + kvm_apic_nmi_wd_deliver(vcpu);
> }
>
> static enum hrtimer_restart pit_timer_fn(struct hrtimer *data)
> @@ -323,6 +311,12 @@ static enum hrtimer_restart pit_timer_fn(struct hrtimer *data)
> return HRTIMER_NORESTART;
> }
>
> +static void kvm_pit_reset_reinject(struct kvm_pit *pit)
> +{
> + atomic_set(&pit->pit_state.pending, 0);
smp_wmb()?
Looks safe otherwise. (Please also add a comment before the memory
barriers to show the pairing).
Paolo
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