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

@@ -133,11 +133,16 @@
         struct nfs4_svgetit_arg sarg;
         struct compound_state cs;
         struct statvfs64 sb;
 
         rfs4_init_compound_state(&cs);
-        cs.vp = ZONE_ROOTVP();
+        /*
+         * 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

@@ -1301,26 +1306,33 @@
         vnode_t *stubvp = NULL, *vp;
 
         vp = sarg->cs->vp;
         sarg->mntdfid_set = FALSE;
 
-        /* VROOT object, must untraverse */
-        if (vp->v_flag & VROOT) {
+        /*
+         * 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
+                 * 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_CMP(vp, ZONE_ROOTVP()));
+                        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);

@@ -1375,14 +1387,14 @@
                 if (sarg->op == NFS4ATTR_SETIT)
                         error = EINVAL;
                 break;          /* this attr is supported */
         case NFS4ATTR_GETIT:
         case NFS4ATTR_VERIT:
-                if (! sarg->mntdfid_set)
+                if (!sarg->mntdfid_set)
                         error = rfs4_get_mntdfileid(cmd, sarg);
 
-                if (! error && sarg->mntdfid_set) {
+                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)