Return appropriate error codes if setting up the GHCB scratch area for an
SEV-ES guest fails. In particular, returning -EINVAL instead of -ENOMEM
when allocating the kernel buffer could be confusing as userspace would
likely suspect a guest issue.
Based on previous feedback and to implement the changes to the GHCB specification, I'm planning on submitting a patch that will return an error code back to the guest, instead of terminating the guest, if the scratch area fails to be setup properly. So you could hold off on this patch if you want.