[PATCH 6/6] KVM: x86: WARN if a vCPU gets a valid wakeup that KVM can't yet inject

[Sean Christopherson <seanjc@google.com>]

WARN if a blocking vCPU is awaked by a valid wake event that KVM can't
inject, e.g. because KVM needs to completed a nested VM-enter, or needs to
re-inject an exception.  For the nested VM-Enter case, KVM is supposed to
clear "nested_run_pending" if L1 puts L2 into HLT, i.e. entering HLT
"completes" the nested VM-Enter.  And for already-injected exceptions, it
should be impossible for the vCPU to be in a blocking state if a VM-Exit
occurred while an exception was being vectored.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/x86.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 82442960b499..f6ace2bd7124 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11233,7 +11233,10 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu)
 	 * causes a spurious wakeup from HLT).
 	 */
 	if (is_guest_mode(vcpu)) {
-		if (kvm_check_nested_events(vcpu) < 0)
+		int r = kvm_check_nested_events(vcpu);
+
+		WARN_ON_ONCE(r == -EBUSY);
+		if (r < 0)
 			return 0;
 	}
 
-- 
2.45.2.505.gda0bf45e8d-goog