From 299018f44ac553dce3caf84df1d14c4764faa279 Mon Sep 17 00:00:00 2001 From: Gleb Natapov Date: Mon, 3 Jun 2013 11:30:02 +0300 Subject: [PATCH] KVM: Fix race in apic->pending_events processing apic->pending_events processing has a race that may cause INIT and SIPI processing to be reordered: vpu0: vcpu1: set INIT test_and_clear_bit(KVM_APIC_INIT) process INIT set INIT set SIPI test_and_clear_bit(KVM_APIC_SIPI) process SIPI At the end INIT is left pending in pending_events. The following patch fixes this by latching pending event before processing them. Signed-off-by: Gleb Natapov --- arch/x86/kvm/lapic.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index e1adbb4aca75..0eee2c8b64d1 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1861,11 +1861,14 @@ void kvm_apic_accept_events(struct kvm_vcpu *vcpu) { struct kvm_lapic *apic = vcpu->arch.apic; unsigned int sipi_vector; + unsigned long pe; - if (!kvm_vcpu_has_lapic(vcpu)) + if (!kvm_vcpu_has_lapic(vcpu) || !apic->pending_events) return; - if (test_and_clear_bit(KVM_APIC_INIT, &apic->pending_events)) { + pe = xchg(&apic->pending_events, 0); + + if (test_bit(KVM_APIC_INIT, &pe)) { kvm_lapic_reset(vcpu); kvm_vcpu_reset(vcpu); if (kvm_vcpu_is_bsp(apic->vcpu)) @@ -1873,7 +1876,7 @@ void kvm_apic_accept_events(struct kvm_vcpu *vcpu) else vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED; } - if (test_and_clear_bit(KVM_APIC_SIPI, &apic->pending_events) && + if (test_bit(KVM_APIC_SIPI, &pe) && vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) { /* evaluate pending_events before reading the vector */ smp_rmb(); -- 2.11.0