KVM: x86: check for interrupts before deciding whether to exit the fast path

The kvm_x86_sync_pir_to_irr callback can sometimes set KVM_REQ_EVENT.
If that happens exactly at the time that an exit is handled as
EXIT_FASTPATH_REENTER_GUEST, vcpu_enter_guest will go incorrectly
through the loop that calls kvm_x86_run, instead of processing
the request promptly.

Fixes: 379a3c8e ("KVM: VMX: Optimize posted-interrupt delivery for timer fastpath")
Cc: stable@vger.kernel.org
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -9643,13 +9643,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		if (likely(exit_fastpath != EXIT_FASTPATH_REENTER_GUEST))
 			break;
 
+		if (vcpu->arch.apicv_active)
+			static_call(kvm_x86_sync_pir_to_irr)(vcpu);
+
 		if (unlikely(kvm_vcpu_exit_request(vcpu))) {
 			exit_fastpath = EXIT_FASTPATH_EXIT_HANDLED;
 			break;
 		}
-
-		if (vcpu->arch.apicv_active)
-			static_call(kvm_x86_sync_pir_to_irr)(vcpu);
 	}
 
 	/*