patches/KVM-lapic-mark-LAPIC-timer-handler-as-irqsafe.patch

From: Marcelo Tosatti <mtosatti@redhat.com>
Date: Wed, 8 Apr 2015 20:33:25 -0300
Subject: KVM: lapic: mark LAPIC timer handler as irqsafe

Since lapic timer handler only wakes up a simple waitqueue,
it can be executed from hardirq context.

Also handle the case where hrtimer_start_expires fails due to -ETIME,
by injecting the interrupt to the guest immediately.

Reduces average cyclictest latency by 3us.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 arch/x86/kvm/lapic.c |   40 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 3 deletions(-)

--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1167,8 +1167,36 @@ void wait_lapic_expire(struct kvm_vcpu *
 		__delay(tsc_deadline - guest_tsc);
 }
 
+static enum hrtimer_restart apic_timer_fn(struct hrtimer *data);
+
+static void __apic_timer_expired(struct hrtimer *data)
+{
+	int ret, i = 0;
+	enum hrtimer_restart r;
+	struct kvm_timer *ktimer = container_of(data, struct kvm_timer, timer);
+
+	r = apic_timer_fn(data);
+
+	if (r == HRTIMER_RESTART) {
+		do {
+			ret = hrtimer_start_expires(data, HRTIMER_MODE_ABS);
+			if (ret == -ETIME)
+				hrtimer_add_expires_ns(&ktimer->timer,
+						       ktimer->period);
+			i++;
+		} while (ret == -ETIME && i < 10);
+
+		if (ret == -ETIME) {
+			printk_once(KERN_ERR "%s: failed to reprogram timer\n",
+				    __func__);
+			WARN_ON_ONCE(1);
+		}
+	}
+}
+
 static void start_apic_timer(struct kvm_lapic *apic)
 {
+	int ret;
 	ktime_t now;
 
 	atomic_set(&apic->lapic_timer.pending, 0);
@@ -1199,9 +1227,11 @@ static void start_apic_timer(struct kvm_
 			}
 		}
 
-		hrtimer_start(&apic->lapic_timer.timer,
+		ret = hrtimer_start(&apic->lapic_timer.timer,
 			      ktime_add_ns(now, apic->lapic_timer.period),
 			      HRTIMER_MODE_ABS);
+		if (ret == -ETIME)
+			__apic_timer_expired(&apic->lapic_timer.timer);
 
 		apic_debug("%s: bus cycle is %" PRId64 "ns, now 0x%016"
 			   PRIx64 ", "
@@ -1233,8 +1263,10 @@ static void start_apic_timer(struct kvm_
 			do_div(ns, this_tsc_khz);
 			expire = ktime_add_ns(now, ns);
 			expire = ktime_sub_ns(expire, lapic_timer_advance_ns);
-			hrtimer_start(&apic->lapic_timer.timer,
+			ret = hrtimer_start(&apic->lapic_timer.timer,
 				      expire, HRTIMER_MODE_ABS);
+			if (ret == -ETIME)
+				__apic_timer_expired(&apic->lapic_timer.timer);
 		} else
 			apic_timer_expired(apic);
 
@@ -1707,6 +1739,7 @@ int kvm_create_lapic(struct kvm_vcpu *vc
 	hrtimer_init(&apic->lapic_timer.timer, CLOCK_MONOTONIC,
 		     HRTIMER_MODE_ABS);
 	apic->lapic_timer.timer.function = apic_timer_fn;
+	apic->lapic_timer.timer.irqsafe = 1;
 
 	/*
 	 * APIC is created enabled. This will prevent kvm_lapic_set_base from
@@ -1834,7 +1867,8 @@ void __kvm_migrate_apic_timer(struct kvm
 
 	timer = &vcpu->arch.apic->lapic_timer.timer;
 	if (hrtimer_cancel(timer))
-		hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
+		if (hrtimer_start_expires(timer, HRTIMER_MODE_ABS) == -ETIME)
+			__apic_timer_expired(timer);
 }
 
 /*