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Commit 299018f4 authored by Gleb Natapov's avatar Gleb Natapov
Browse files

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: default avatarGleb Natapov <gleb@redhat.com>
parent 8acb4207

arch/x86/kvm/lapic.c

+6 −3
Original line number Diff line number Diff line
@@ -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();