From: Marcelo Tosatti <mtosatti@redhat.com>
Date: Tue, 28 Jul 2009 02:41:01 +0000 (-0300)
Subject: KVM: limit lapic periodic timer frequency
X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=1444885a045fe3b1905a14ea1b52540bf556578b;p=deliverable%2Flinux.git

KVM: limit lapic periodic timer frequency

Otherwise its possible to starve the host by programming lapic timer
with a very high frequency.

Cc: stable@kernel.org
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
---

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 66122bfc74a9..5b9d1ae09cad 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -670,6 +670,15 @@ static void start_apic_timer(struct kvm_lapic *apic)
 
 	if (!apic->lapic_timer.period)
 		return;
+	/*
+	 * Do not allow the guest to program periodic timers with small
+	 * interval, since the hrtimers are not throttled by the host
+	 * scheduler.
+	 */
+	if (apic_lvtt_period(apic)) {
+		if (apic->lapic_timer.period < NSEC_PER_MSEC/2)
+			apic->lapic_timer.period = NSEC_PER_MSEC/2;
+	}
 
 	hrtimer_start(&apic->lapic_timer.timer,
 		      ktime_add_ns(now, apic->lapic_timer.period),