Re: [PATCH] Fix almost infinite loop in APIC

[Sheng Yang <sheng@linux.intel.com>]

On Wednesday 21 January 2009 12:23:30 Marcelo Tosatti wrote:
> On Wed, Jan 21, 2009 at 10:40:49AM +0800, Sheng Yang wrote:
> > Mind continue to change...
> >
> > A: time_fire
> > B: intr_post
> > C: read TMCCT
> >
> > I think the sequence can be AABC or AACB(I just consider AABC last
> > night...). We have determined to return A->C as TMCCT, and the interval
> > between different A is period which can be ignored. So how about simply
> > return
> > hrtimer_expires_remaining() for all tmcct reading including pending ones?
> >
> > (And sorry for I still can't get why you return injection delay for
> > TMCCT...)
>
> You're right. How about this.
>
>
> diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
> index c019b8e..cf17ed5 100644
> --- a/arch/x86/kvm/irq.c
> +++ b/arch/x86/kvm/irq.c
> @@ -87,13 +87,6 @@ void kvm_inject_pending_timer_irqs(struct kvm_vcpu
> *vcpu) }
>  EXPORT_SYMBOL_GPL(kvm_inject_pending_timer_irqs);
>
> -void kvm_timer_intr_post(struct kvm_vcpu *vcpu, int vec)
> -{
> -	kvm_apic_timer_intr_post(vcpu, vec);
> -	/* TODO: PIT, RTC etc. */
> -}
> -EXPORT_SYMBOL_GPL(kvm_timer_intr_post);
> -
>  void __kvm_migrate_timers(struct kvm_vcpu *vcpu)
>  {
>  	__kvm_migrate_apic_timer(vcpu);
> diff --git a/arch/x86/kvm/irq.h b/arch/x86/kvm/irq.h
> index 2bf32a0..82579ee 100644
> --- a/arch/x86/kvm/irq.h
> +++ b/arch/x86/kvm/irq.h
> @@ -89,7 +89,6 @@ static inline int irqchip_in_kernel(struct kvm *kvm)
>
>  void kvm_pic_reset(struct kvm_kpic_state *s);
>
> -void kvm_timer_intr_post(struct kvm_vcpu *vcpu, int vec);
>  void kvm_inject_pending_timer_irqs(struct kvm_vcpu *vcpu);
>  void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu);
>  void kvm_apic_nmi_wd_deliver(struct kvm_vcpu *vcpu);
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index afac68c..b66f71e 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -511,52 +511,22 @@ static void apic_send_ipi(struct kvm_lapic *apic)
>
>  static u32 apic_get_tmcct(struct kvm_lapic *apic)
>  {
> -	u64 counter_passed;
> -	ktime_t passed, now;
> +	ktime_t remaining;
> +	s64 ns;
>  	u32 tmcct;
>
>  	ASSERT(apic != NULL);
>
> -	now = apic->timer.dev.base->get_time();
> -	tmcct = apic_get_reg(apic, APIC_TMICT);
> -
>  	/* if initial count is 0, current count should also be 0 */
> -	if (tmcct == 0)
> +	if (apic_get_reg(apic, APIC_TMICT) == 0)
>  		return 0;
>
> -	if (unlikely(ktime_to_ns(now) <=
> -		ktime_to_ns(apic->timer.last_update))) {
> -		/* Wrap around */
> -		passed = ktime_add(( {
> -				    (ktime_t) {
> -				    .tv64 = KTIME_MAX -
> -				    (apic->timer.last_update).tv64}; }
> -				   ), now);
> -		apic_debug("time elapsed\n");
> -	} else
> -		passed = ktime_sub(now, apic->timer.last_update);
> -
> -	counter_passed = div64_u64(ktime_to_ns(passed),
> -				   (APIC_BUS_CYCLE_NS * apic->timer.divide_count));
> -
> -	if (counter_passed > tmcct) {
> -		if (unlikely(!apic_lvtt_period(apic))) {
> -			/* one-shot timers stick at 0 until reset */
> -			tmcct = 0;
> -		} else {
> -			/*
> -			 * periodic timers reset to APIC_TMICT when they
> -			 * hit 0. The while loop simulates this happening N
> -			 * times. (counter_passed %= tmcct) would also work,
> -			 * but might be slower or not work on 32-bit??
> -			 */
> -			while (counter_passed > tmcct)
> -				counter_passed -= tmcct;
> -			tmcct -= counter_passed;
> -		}
> -	} else {
> -		tmcct -= counter_passed;
> -	}
> +	remaining = hrtimer_expires_remaining(&apic->timer.dev);
> +	if (remaining.tv64 < 0)

Use ktime_to_ns() macro is better.

The remaining parts are fine with me. But please do more test. :)

Thanks for work!

-- 
regards
Yang, Sheng

> +		remaining = ktime_set(0, 0);
> +
> +	ns = ktime_to_ns(remaining) % apic->timer.period;
> +	tmcct = div64_u64(ns, (APIC_BUS_CYCLE_NS * apic->timer.divide_count));
>
>  	return tmcct;
>  }
> @@ -653,8 +623,6 @@ static void start_apic_timer(struct kvm_lapic *apic)
>  {
>  	ktime_t now = apic->timer.dev.base->get_time();
>
> -	apic->timer.last_update = now;
> -
>  	apic->timer.period = apic_get_reg(apic, APIC_TMICT) *
>  		    APIC_BUS_CYCLE_NS * apic->timer.divide_count;
>  	atomic_set(&apic->timer.pending, 0);
> @@ -1110,16 +1078,6 @@ void kvm_inject_apic_timer_irqs(struct kvm_vcpu
> *vcpu) }
>  }
>
> -void kvm_apic_timer_intr_post(struct kvm_vcpu *vcpu, int vec)
> -{
> -	struct kvm_lapic *apic = vcpu->arch.apic;
> -
> -	if (apic && apic_lvt_vector(apic, APIC_LVTT) == vec)
> -		apic->timer.last_update = ktime_add_ns(
> -				apic->timer.last_update,
> -				apic->timer.period);
> -}
> -
>  int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
>  {
>  	int vector = kvm_apic_has_interrupt(vcpu);
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index 8185888..45ab6ee 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -12,7 +12,6 @@ struct kvm_lapic {
>  		atomic_t pending;
>  		s64 period;	/* unit: ns */
>  		u32 divide_count;
> -		ktime_t last_update;
>  		struct hrtimer dev;
>  	} timer;
>  	struct kvm_vcpu *vcpu;
> @@ -42,7 +41,6 @@ void kvm_set_apic_base(struct kvm_vcpu *vcpu, u64 data);
>  void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu);
>  int kvm_lapic_enabled(struct kvm_vcpu *vcpu);
>  int kvm_lapic_find_highest_irr(struct kvm_vcpu *vcpu);
> -void kvm_apic_timer_intr_post(struct kvm_vcpu *vcpu, int vec);
>
>  void kvm_lapic_set_vapic_addr(struct kvm_vcpu *vcpu, gpa_t vapic_addr);
>  void kvm_lapic_sync_from_vapic(struct kvm_vcpu *vcpu);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 14e517e..db5021b 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -2305,7 +2305,6 @@ static void svm_intr_assist(struct kvm_vcpu *vcpu)
>  	/* Okay, we can deliver the interrupt: grab it and update PIC state. */
>  	intr_vector = kvm_cpu_get_interrupt(vcpu);
>  	svm_inject_irq(svm, intr_vector);
> -	kvm_timer_intr_post(vcpu, intr_vector);
>  out:
>  	update_cr8_intercept(vcpu);
>  }
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 9b56d21..25aaf11 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3377,7 +3377,6 @@ static void vmx_intr_assist(struct kvm_vcpu *vcpu)
>  	}
>  	if (vcpu->arch.interrupt.pending) {
>  		vmx_inject_irq(vcpu, vcpu->arch.interrupt.nr);
> -		kvm_timer_intr_post(vcpu, vcpu->arch.interrupt.nr);
>  		if (kvm_cpu_has_interrupt(vcpu))
>  			enable_irq_window(vcpu);
>  	}