KVM: VMX: Consume pending LAPIC INIT event when exit on INIT_SIGNAL

Intel SDM section 25.2 OTHER CAUSES OF VM EXITS specifies the following
on INIT signals: "Such exits do not modify register state or clear pending
events as they would outside of VMX operation."

When commit 4b9852f4f389 ("KVM: x86: Fix INIT signal handling in various CPU states")
was applied, I interepted above Intel SDM statement such that
INIT_SIGNAL exit don’t consume the LAPIC INIT pending event.

However, when Nadav Amit run matching kvm-unit-test on a bare-metal
machine, it turned out my interpetation was wrong. i.e. INIT_SIGNAL
exit does consume the LAPIC INIT pending event.
(See: https://www.spinics.net/lists/kvm/msg196757.html)

Therefore, fix KVM code to behave as observed on bare-metal.

Fixes: 4b9852f4f389 ("KVM: x86: Fix INIT signal handling in various CPU states")
Reported-by: Nadav Amit <nadav.amit@gmail.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 55c5791..cd8d0b0 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3463,6 +3463,7 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
                test_bit(KVM_APIC_INIT, &apic->pending_events)) {
                if (block_nested_events)
                        return -EBUSY;
+               clear_bit(KVM_APIC_INIT, &apic->pending_events);
                nested_vmx_vmexit(vcpu, EXIT_REASON_INIT_SIGNAL, 0, 0);
                return 0;
        }