From 622395a9e63bf87a16faecf555ed02375cbae5b7 Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Wed, 11 Jun 2008 19:52:53 -0300 Subject: [PATCH] KVM: only abort guest entry if timer count goes from 0->1 Only abort guest entry if the timer count went from 0->1, since for 1->2 or larger the bit will either be set already or a timer irq will have been injected. Using atomic_inc_and_test() for it also introduces an SMP barrier to the LAPIC version (thought it was unecessary because of timer migration, but guest can be scheduled to a different pCPU between exit and kvm_vcpu_block(), so there is the possibility for a race). Noticed by Avi. Signed-off-by: Marcelo Tosatti Signed-off-by: Avi Kivity --- arch/x86/kvm/i8254.c | 11 ++++------- arch/x86/kvm/lapic.c | 4 ++-- 2 files changed, 6 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c index 9e3391e..c0f7872 100644 --- a/arch/x86/kvm/i8254.c +++ b/arch/x86/kvm/i8254.c @@ -198,14 +198,11 @@ static int __pit_timer_fn(struct kvm_kpit_state *ps) struct kvm_vcpu *vcpu0 = ps->pit->kvm->vcpus[0]; struct kvm_kpit_timer *pt = &ps->pit_timer; - atomic_inc(&pt->pending); - smp_mb__after_atomic_inc(); - if (vcpu0) { + if (!atomic_inc_and_test(&pt->pending)) set_bit(KVM_REQ_PENDING_TIMER, &vcpu0->requests); - if (waitqueue_active(&vcpu0->wq)) { - vcpu0->arch.mp_state = KVM_MP_STATE_RUNNABLE; - wake_up_interruptible(&vcpu0->wq); - } + if (vcpu0 && waitqueue_active(&vcpu0->wq)) { + vcpu0->arch.mp_state = KVM_MP_STATE_RUNNABLE; + wake_up_interruptible(&vcpu0->wq); } pt->timer.expires = ktime_add_ns(pt->timer.expires, pt->period); diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 180ba73..73f43de 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -945,8 +945,8 @@ static int __apic_timer_fn(struct kvm_lapic *apic) int result = 0; wait_queue_head_t *q = &apic->vcpu->wq; - atomic_inc(&apic->timer.pending); - set_bit(KVM_REQ_PENDING_TIMER, &apic->vcpu->requests); + if(!atomic_inc_and_test(&apic->timer.pending)) + set_bit(KVM_REQ_PENDING_TIMER, &apic->vcpu->requests); if (waitqueue_active(q)) { apic->vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE; wake_up_interruptible(q); -- 2.7.4