KVM: SVM: Update SEV-ES shutdown intercepts with more metadata

Currently if an SEV-ES VM shuts down userspace sees KVM_RUN struct with
only errno=EINVAL. This is a very limited amount of information to debug
the situation. Instead return KVM_EXIT_SHUTDOWN to alert userspace the VM
is shutting down and is not usable any further.

Signed-off-by: Peter Gonda <pgonda@google.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Suggested-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20230907162449.1739785-1-pgonda@google.com
[sean: tweak changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/svm/svm.c

@@ -2203,12 +2203,6 @@ static int shutdown_interception(struct kvm_vcpu *vcpu)
 	struct kvm_run *kvm_run = vcpu->run;
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	/*
-	 * The VM save area has already been encrypted so it
-	 * cannot be reinitialized - just terminate.
-	 */
-	if (sev_es_guest(vcpu->kvm))
-		return -EINVAL;
 
 	/*
 	 * VMCB is undefined after a SHUTDOWN intercept.  INIT the vCPU to put
@@ -2217,9 +2211,14 @@ static int shutdown_interception(struct kvm_vcpu *vcpu)
 	 * userspace.  At a platform view, INIT is acceptable behavior as
 	 * there exist bare metal platforms that automatically INIT the CPU
 	 * in response to shutdown.
+	 *
+	 * The VM save area for SEV-ES guests has already been encrypted so it
+	 * cannot be reinitialized, i.e. synthesizing INIT is futile.
 	 */
-	clear_page(svm->vmcb);
-	kvm_vcpu_reset(vcpu, true);
+	if (!sev_es_guest(vcpu->kvm)) {
+		clear_page(svm->vmcb);
+		kvm_vcpu_reset(vcpu, true);
+	}
 
 	kvm_run->exit_reason = KVM_EXIT_SHUTDOWN;
 	return 0;