From: Marcelo Tosatti <mtosatti@redhat.com>
Date: Fri, 18 Sep 2009 23:08:05 +0000 (-0300)
Subject: KVM: limit lapic periodic timer frequency
X-Git-Tag: v2.6.30.9~21
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d1dbc751eb2a4aaf628cc9dac6954e1bd1afc531;p=thirdparty%2Fkernel%2Fstable.git

KVM: limit lapic periodic timer frequency

(cherry picked from commit 1444885a045fe3b1905a14ea1b52540bf556578b)

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

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index f0b67f2cdd695..dba1f4d08f2c4 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -635,6 +635,15 @@ static void start_apic_timer(struct kvm_lapic *apic)
 
 	if (!apic->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->timer.period < NSEC_PER_MSEC/2)
+			apic->timer.period = NSEC_PER_MSEC/2;
+	}
 
 	hrtimer_start(&apic->timer.dev,
 		      ktime_add_ns(now, apic->timer.period),