+
+       switch (request) {
+       case SVM_VMGEXIT_AP_CREATE_ON_INIT:
+               kick = false;
+               fallthrough;
+       case SVM_VMGEXIT_AP_CREATE:
+               if (!page_address_valid(vcpu, svm->vmcb->control.exit_info_2)) {
+                       vcpu_unimpl(vcpu, "vmgexit: invalid AP VMSA address [%#llx] from guest\n",
+                                   svm->vmcb->control.exit_info_2);
+                       ret = -EINVAL;
+                       goto out;
+               }
+
+               /*
+                * Malicious guest can RMPADJUST a large page into VMSA which
+                * will hit the SNP erratum where the CPU will incorrectly signal
+                * an RMP violation #PF if a hugepage collides with the RMP entry
+                * of VMSA page, reject the AP CREATE request if VMSA address from
+                * guest is 2M aligned.
+                */
+               if (IS_ALIGNED(svm->vmcb->control.exit_info_2, PMD_SIZE)) {
+                       vcpu_unimpl(vcpu,
+                                   "vmgexit: AP VMSA address [%llx] from guest is unsafe as it is 2M aligned\n",
+                                   svm->vmcb->control.exit_info_2);

In this case and maybe the above case can we instead return an error
to the guest instead of a #GP?

I think Tom suggested: SW_EXITINFO1[31:0] to 2 (meaning there was an
error with the VMGEXIT request) and SW_EXITINFO2 to 5 (The NAE event
input was not valid (e.g., an invalid SW_EXITINFO1 value for the AP
Jump Table NAE event).

This way a non-malicious but buggy or naive guest gets a little more
information and a chance to retry the request?

+                       ret = -EINVAL;
+                       goto out;
+               }
+
+               target_svm->sev_es.snp_vmsa_gpa = svm->vmcb->control.exit_info_2;
+               break;
+       case SVM_VMGEXIT_AP_DESTROY:
+               break;
+       default:
+               vcpu_unimpl(vcpu, "vmgexit: invalid AP creation request [%#x] from guest\n",
+                           request);
+               ret = -EINVAL;
+               break;
+       }
+