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KVM: Fix race in apic->pending_events processing

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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 <gleb@redhat.com>
This commit is contained in:
Gleb Natapov 2013-06-03 11:30:02 +03:00
parent 8acb42070e
commit 299018f44a
1 changed files with 6 additions and 3 deletions
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9
arch/x86/kvm/lapic.c
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@ -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();