From 1444885a045fe3b1905a14ea1b52540bf556578b Mon Sep 17 00:00:00 2001
From: Marcelo Tosatti <mtosatti@redhat.com>
Date: Mon, 27 Jul 2009 23:41:01 -0300
Subject: [PATCH] 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>
---
arch/x86/kvm/lapic.c | 9 +++++++++
1 file changed, 9 insertions(+)
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),
--
2.34.1