KVM: SVM: Cannot re-initialize the VMCB after shutdown with SEV-ES

When a SHUTDOWN VMEXIT is encountered, normally the VMCB is re-initialized
so that the guest can be re-launched. But when a guest is running as an
SEV-ES guest, the VMSA cannot be re-initialized because it has been
encrypted. For now, just return -EINVAL to prevent a possible attempt at
a guest reset.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <aa6506000f6f3a574de8dbcdab0707df844cb00c.1607620209.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/svm.c

@@ -2010,6 +2010,13 @@ static int shutdown_interception(struct vcpu_svm *svm)
 {
 	struct kvm_run *kvm_run = svm->vcpu.run;
 
+	/*
+	 * The VM save area has already been encrypted so it
+	 * cannot be reinitialized - just terminate.
+	 */
+	if (sev_es_guest(svm->vcpu.kvm))
+		return -EINVAL;
+
 	/*
 	 * VMCB is undefined after a SHUTDOWN intercept
 	 * so reinitialize it.