diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 0d79a88f4de9..e4f84f013b57 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1686,6 +1686,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			The default is to send the implementation identification
 			information.
 
+	nfsd.nfs4_disable_idmapping=
+			[NFSv4] When set to the default of '1', the NFSv4
+			server will return only numeric uids and gids to
+			clients using auth_sys, and will accept numeric uids
+			and gids from such clients.  This is intended to ease
+			migration from NFSv2/v3.
 
 	objlayoutdriver.osd_login_prog=
 			[NFS] [OBJLAYOUT] sets the pathname to the program which
diff --git a/fs/nfsd/nfs4idmap.c b/fs/nfsd/nfs4idmap.c
index 94096273cd6c..69ca9c5bb600 100644
--- a/fs/nfsd/nfs4idmap.c
+++ b/fs/nfsd/nfs4idmap.c
@@ -40,6 +40,14 @@
 #include "idmap.h"
 #include "nfsd.h"
 
+/*
+ * Turn off idmapping when using AUTH_SYS.
+ */
+static bool nfs4_disable_idmapping = true;
+module_param(nfs4_disable_idmapping, bool, 0644);
+MODULE_PARM_DESC(nfs4_disable_idmapping,
+		"Turn off server's NFSv4 idmapping when using 'sec=sys'");
+
 /*
  * Cache entry
  */
@@ -561,28 +569,65 @@ idmap_id_to_name(struct svc_rqst *rqstp, int type, uid_t id, char *name)
 	return ret;
 }
 
+static bool
+numeric_name_to_id(struct svc_rqst *rqstp, int type, const char *name, u32 namelen, uid_t *id)
+{
+	int ret;
+	char buf[11];
+
+	if (namelen + 1 > sizeof(buf))
+		/* too long to represent a 32-bit id: */
+		return false;
+	/* Just to make sure it's null-terminated: */
+	memcpy(buf, name, namelen);
+	buf[namelen] = '\0';
+	ret = strict_strtoul(name, 10, (unsigned long *)id);
+	return ret == 0;
+}
+
+static __be32
+do_name_to_id(struct svc_rqst *rqstp, int type, const char *name, u32 namelen, uid_t *id)
+{
+	if (nfs4_disable_idmapping && rqstp->rq_flavor < RPC_AUTH_GSS)
+		if (numeric_name_to_id(rqstp, type, name, namelen, id))
+			return 0;
+		/*
+		 * otherwise, fall through and try idmapping, for
+		 * backwards compatibility with clients sending names:
+		 */
+	return idmap_name_to_id(rqstp, type, name, namelen, id);
+}
+
+static int
+do_id_to_name(struct svc_rqst *rqstp, int type, uid_t id, char *name)
+{
+	if (nfs4_disable_idmapping && rqstp->rq_flavor < RPC_AUTH_GSS)
+		return sprintf(name, "%u", id);
+	return idmap_id_to_name(rqstp, type, id, name);
+}
+
 __be32
 nfsd_map_name_to_uid(struct svc_rqst *rqstp, const char *name, size_t namelen,
 		__u32 *id)
 {
-	return idmap_name_to_id(rqstp, IDMAP_TYPE_USER, name, namelen, id);
+	return do_name_to_id(rqstp, IDMAP_TYPE_USER, name, namelen, id);
 }
 
 __be32
 nfsd_map_name_to_gid(struct svc_rqst *rqstp, const char *name, size_t namelen,
 		__u32 *id)
 {
-	return idmap_name_to_id(rqstp, IDMAP_TYPE_GROUP, name, namelen, id);
+	return do_name_to_id(rqstp, IDMAP_TYPE_GROUP, name, namelen, id);
 }
 
 int
 nfsd_map_uid_to_name(struct svc_rqst *rqstp, __u32 id, char *name)
 {
-	return idmap_id_to_name(rqstp, IDMAP_TYPE_USER, id, name);
+	return do_id_to_name(rqstp, IDMAP_TYPE_USER, id, name);
 }
 
 int
 nfsd_map_gid_to_name(struct svc_rqst *rqstp, __u32 id, char *name)
 {
-	return idmap_id_to_name(rqstp, IDMAP_TYPE_GROUP, id, name);
+	return do_id_to_name(rqstp, IDMAP_TYPE_GROUP, id, name);
 }