Re: [PATCH] Fix almost infinite loop in APIC

[Marcelo Tosatti <mtosatti@redhat.com>]

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)
+		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);
 	}