From a5d36f82c4f3e852b61fdf1fee13463c8aa91b90 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Tue, 29 Dec 2009 12:42:16 +0200 Subject: [PATCH] KVM: Fix race between APIC TMR and IRR When we queue an interrupt to the local apic, we set the IRR before the TMR. The vcpu can pick up the IRR and inject the interrupt before setting the TMR, and perhaps even EOI it, causing incorrect behaviour. The race is really insignificant since it can only occur on the first interrupt (usually following interrupts will not change TMR), but it's better closed than open. Fixed by reordering setting the TMR vs IRR. Cc: stable@kernel.org Signed-off-by: Avi Kivity Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/lapic.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 3063a0c4858b..ba8c045da782 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -373,6 +373,12 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode, if (unlikely(!apic_enabled(apic))) break; + if (trig_mode) { + apic_debug("level trig mode for vector %d", vector); + apic_set_vector(vector, apic->regs + APIC_TMR); + } else + apic_clear_vector(vector, apic->regs + APIC_TMR); + result = !apic_test_and_set_irr(vector, apic); trace_kvm_apic_accept_irq(vcpu->vcpu_id, delivery_mode, trig_mode, vector, !result); @@ -383,11 +389,6 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode, break; } - if (trig_mode) { - apic_debug("level trig mode for vector %d", vector); - apic_set_vector(vector, apic->regs + APIC_TMR); - } else - apic_clear_vector(vector, apic->regs + APIC_TMR); kvm_vcpu_kick(vcpu); break;