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 and INIT is left pending in pending_events. The following patch
tries to fix this using the fact that if INIT comes after SIPI it drops
SIPI from the pending_events, so if pending_events is different after
SIPI is processed it means that INIT was issued after SIPI otherwise
all pending event are processed and pending_events can be reset to zero.
Signed-off-by: Gleb Natapov <g...@redhat.com>
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 9d75193..67686b8 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1850,6 +1850,7 @@ 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))
return;
@@ -1862,7 +1863,8 @@ 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) &&
+ pe = 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();
@@ -1871,6 +1873,7 @@ void kvm_apic_accept_events(struct kvm_vcpu *vcpu)
vcpu->vcpu_id, sipi_vector);
kvm_vcpu_deliver_sipi_vector(vcpu, sipi_vector);
vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
+ cmpxchg(&apic->pending_events, pe, 0);
}
}
--
Gleb.
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