Be far more judicious in the use of curzone-using macros.
(Merge and extra asserts by danmcd.)
Try to remove assumption that zone's root vnode is marked VROOT

*** 133,143 ****
          struct nfs4_svgetit_arg sarg;
          struct compound_state cs;
          struct statvfs64 sb;
  
          rfs4_init_compound_state(&cs);
!         cs.vp = ZONE_ROOTVP();
          cs.fh.nfs_fh4_val = NULL;
          cs.cr = kcred;
  
          /*
           * Get all the supported attributes
--- 133,148 ----
          struct nfs4_svgetit_arg sarg;
          struct compound_state cs;
          struct statvfs64 sb;
  
          rfs4_init_compound_state(&cs);
!         /*
!          * This is global state checking, called once. We might be in
!          * non-global-zone context here (say a modload happens from a zone
!          * process) so in this case, we want the global-zone root vnode.
!          */
!         cs.vp = rootvp;
          cs.fh.nfs_fh4_val = NULL;
          cs.cr = kcred;
  
          /*
           * Get all the supported attributes
*** 1301,1326 ****
          vnode_t *stubvp = NULL, *vp;
  
          vp = sarg->cs->vp;
          sarg->mntdfid_set = FALSE;
  
!         /* VROOT object, must untraverse */
!         if (vp->v_flag & VROOT) {
  
                  /* extra hold for vp since untraverse might rele */
                  VN_HOLD(vp);
                  stubvp = untraverse(vp);
  
                  /*
!                  * If vp/stubvp are same, we must be at system
                   * root because untraverse returned same vp
                   * for a VROOT object.  sarg->vap was setup
                   * before we got here, so there's no need to do
                   * another getattr -- just use the one in sarg.
                   */
                  if (VN_CMP(vp, stubvp)) {
!                         ASSERT(VN_CMP(vp, ZONE_ROOTVP()));
                          vap = sarg->vap;
                  } else {
                          va.va_mask = AT_NODEID;
                          vap = &va;
                          error = rfs4_vop_getattr(stubvp, vap, 0, sarg->cs->cr);
--- 1306,1338 ----
          vnode_t *stubvp = NULL, *vp;
  
          vp = sarg->cs->vp;
          sarg->mntdfid_set = FALSE;
  
!         /*
!          * VROOT object or zone's root, must untraverse.
!          *
!          * NOTE: Not doing reality checks on curzone vs. compound
!          * state vnode because it will mismatch once at initialization
!          * if a non-global-zone triggers the module load, BUT in that case
!          * the vp is literally "/" which has VROOT set.
!          */
!         if ((vp->v_flag & VROOT) || VN_IS_CURZONEROOT(vp)) {
  
                  /* extra hold for vp since untraverse might rele */
                  VN_HOLD(vp);
                  stubvp = untraverse(vp);
  
                  /*
!                  * If vp/stubvp are same, we must be at system-or-zone
                   * root because untraverse returned same vp
                   * for a VROOT object.  sarg->vap was setup
                   * before we got here, so there's no need to do
                   * another getattr -- just use the one in sarg.
                   */
                  if (VN_CMP(vp, stubvp)) {
!                         ASSERT(VN_IS_CURZONEROOT(vp));
                          vap = sarg->vap;
                  } else {
                          va.va_mask = AT_NODEID;
                          vap = &va;
                          error = rfs4_vop_getattr(stubvp, vap, 0, sarg->cs->cr);
*** 1375,1388 ****
                  if (sarg->op == NFS4ATTR_SETIT)
                          error = EINVAL;
                  break;          /* this attr is supported */
          case NFS4ATTR_GETIT:
          case NFS4ATTR_VERIT:
!                 if (! sarg->mntdfid_set)
                          error = rfs4_get_mntdfileid(cmd, sarg);
  
!                 if (! error && sarg->mntdfid_set) {
                          if (cmd == NFS4ATTR_GETIT)
                                  na->mounted_on_fileid = sarg->mounted_on_fileid;
                          else
                                  if (na->mounted_on_fileid !=
                                      sarg->mounted_on_fileid)
--- 1387,1400 ----
                  if (sarg->op == NFS4ATTR_SETIT)
                          error = EINVAL;
                  break;          /* this attr is supported */
          case NFS4ATTR_GETIT:
          case NFS4ATTR_VERIT:
!                 if (!sarg->mntdfid_set)
                          error = rfs4_get_mntdfileid(cmd, sarg);
  
!                 if (!error && sarg->mntdfid_set) {
                          if (cmd == NFS4ATTR_GETIT)
                                  na->mounted_on_fileid = sarg->mounted_on_fileid;
                          else
                                  if (na->mounted_on_fileid !=
                                      sarg->mounted_on_fileid)