From b606f189c7d5bf9b875bba168162fe05287880fe Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Mon, 20 Jun 2016 22:33:48 -0300 Subject: [PATCH] KVM: LAPIC: cap __delay at lapic_timer_advance_ns The host timer which emulates the guest LAPIC TSC deadline timer has its expiration diminished by lapic_timer_advance_ns nanoseconds. Therefore if, at wait_lapic_expire, a difference larger than lapic_timer_advance_ns is encountered, delay at most lapic_timer_advance_ns. This fixes a problem where the guest can cause the host to delay for large amounts of time. Reported-by: Alan Jenkins Signed-off-by: Marcelo Tosatti Signed-off-by: Paolo Bonzini --- arch/x86/kvm/lapic.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index bbb5b283ff63..a397200281c1 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1310,7 +1310,8 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu) /* __delay is delay_tsc whenever the hardware has TSC, thus always. */ if (guest_tsc < tsc_deadline) - __delay(tsc_deadline - guest_tsc); + __delay(min(tsc_deadline - guest_tsc, + nsec_to_cycles(vcpu, lapic_timer_advance_ns))); } static void start_apic_timer(struct kvm_lapic *apic)