KVM: SVM: Do not set sev->es_active until KVM_SEV_ES_INIT completes

Set sev->es_active only after the guts of KVM_SEV_ES_INIT succeeds.  If
the command fails, e.g. because SEV is already active or there are no
available ASIDs, then es_active will be left set even though the VM is
not fully SEV-ES capable.

Refactor the code so that "es_active" is passed on the stack instead of
being prematurely shoved into sev_info, both to avoid having to unwind
sev_info and so that it's more obvious what actually consumes es_active
in sev_guest_init() and its helpers.

Fixes: ad73109a ("KVM: SVM: Provide support to launch and run an SEV-ES guest")
Cc: stable@vger.kernel.org
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210331031936.2495277-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/sev.c

@@ -87,7 +87,7 @@ static bool __sev_recycle_asids(int min_asid, int max_asid)
 	return true;
 }
 
-static int sev_asid_new(struct kvm_sev_info *sev)
+static int sev_asid_new(bool es_active)
 {
 	int pos, min_asid, max_asid;
 	bool retry = true;
@@ -98,8 +98,8 @@ static int sev_asid_new(struct kvm_sev_info *sev)
 	 * SEV-enabled guests must use asid from min_sev_asid to max_sev_asid.
 	 * SEV-ES-enabled guest can use from 1 to min_sev_asid - 1.
 	 */
-	min_asid = sev->es_active ? 0 : min_sev_asid - 1;
-	max_asid = sev->es_active ? min_sev_asid - 1 : max_sev_asid;
+	min_asid = es_active ? 0 : min_sev_asid - 1;
+	max_asid = es_active ? min_sev_asid - 1 : max_sev_asid;
 again:
 	pos = find_next_zero_bit(sev_asid_bitmap, max_sev_asid, min_asid);
 	if (pos >= max_asid) {
@@ -179,13 +179,14 @@ static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
 static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
 {
 	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+	bool es_active = argp->id == KVM_SEV_ES_INIT;
 	int asid, ret;
 
 	ret = -EBUSY;
 	if (unlikely(sev->active))
 		return ret;
 
-	asid = sev_asid_new(sev);
+	asid = sev_asid_new(es_active);
 	if (asid < 0)
 		return ret;
 
@@ -194,6 +195,7 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
 		goto e_free;
 
 	sev->active = true;
+	sev->es_active = es_active;
 	sev->asid = asid;
 	INIT_LIST_HEAD(&sev->regions_list);
 
@@ -204,16 +206,6 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	return ret;
 }
 
-static int sev_es_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
-{
-	if (!sev_es)
-		return -ENOTTY;
-
-	to_kvm_svm(kvm)->sev_info.es_active = true;
-
-	return sev_guest_init(kvm, argp);
-}
-
 static int sev_bind_asid(struct kvm *kvm, unsigned int handle, int *error)
 {
 	struct sev_data_activate *data;
@@ -1128,12 +1120,15 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 	mutex_lock(&kvm->lock);
 
 	switch (sev_cmd.id) {
+	case KVM_SEV_ES_INIT:
+		if (!sev_es) {
+			r = -ENOTTY;
+			goto out;
+		}
+		fallthrough;
 	case KVM_SEV_INIT:
 		r = sev_guest_init(kvm, &sev_cmd);
 		break;
-	case KVM_SEV_ES_INIT:
-		r = sev_es_guest_init(kvm, &sev_cmd);
-		break;
 	case KVM_SEV_LAUNCH_START:
 		r = sev_launch_start(kvm, &sev_cmd);
 		break;