diff --git a/tools/libxl/libxl_psr.c b/tools/libxl/libxl_psr.c
index 2a077773ab..33782394a2 100644
--- a/tools/libxl/libxl_psr.c
+++ b/tools/libxl/libxl_psr.c
@@ -31,7 +31,7 @@ static void libxl__psr_log_err_msg(libxl__gc *gc, int err)
     case ESRCH:
         msg = "invalid domain ID";
         break;
-    case EBADSLT:
+    case ENOTSOCK:
         msg = "socket is not supported";
         break;
     case EFAULT:
@@ -59,7 +59,7 @@ static void libxl__psr_cmt_log_err_msg(libxl__gc *gc, int err)
     case ENOENT:
         msg = "CMT is not attached to this domain";
         break;
-    case EUSERS:
+    case EOVERFLOW:
         msg = "no free RMID available";
         break;
     default:
@@ -81,7 +81,7 @@ static void libxl__psr_cat_log_err_msg(libxl__gc *gc, int err)
     case ENOENT:
         msg = "CAT is not enabled on the socket";
         break;
-    case EUSERS:
+    case EOVERFLOW:
         msg = "no free COS available";
         break;
     case EEXIST:
diff --git a/xen/arch/x86/mm/paging.c b/xen/arch/x86/mm/paging.c
index 708915515e..942d8491fc 100644
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -766,7 +766,7 @@ long paging_domctl_continuation(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
 
     if ( op.interface_version != XEN_DOMCTL_INTERFACE_VERSION ||
          op.cmd != XEN_DOMCTL_shadow_op )
-        return -EBADRQC;
+        return -EOPNOTSUPP;
 
     d = rcu_lock_domain_by_id(op.domain);
     if ( d == NULL )
diff --git a/xen/arch/x86/psr.c b/xen/arch/x86/psr.c
index ed59803573..c0daa2effe 100644
--- a/xen/arch/x86/psr.c
+++ b/xen/arch/x86/psr.c
@@ -178,7 +178,7 @@ int psr_alloc_rmid(struct domain *d)
     if ( rmid > psr_cmt->rmid_max )
     {
         d->arch.psr_rmid = 0;
-        return -EUSERS;
+        return -EOVERFLOW;
     }
 
     d->arch.psr_rmid = rmid;
@@ -253,7 +253,7 @@ static struct psr_cat_socket_info *get_cat_socket_info(unsigned int socket)
         return ERR_PTR(-ENODEV);
 
     if ( socket >= nr_sockets )
-        return ERR_PTR(-EBADSLT);
+        return ERR_PTR(-ENOTSOCK);
 
     if ( !test_bit(socket, cat_socket_enable) )
         return ERR_PTR(-ENOENT);
@@ -334,7 +334,7 @@ static int write_l3_cbm(unsigned int socket, unsigned int cos, uint64_t cbm)
         unsigned int cpu = get_socket_cpu(socket);
 
         if ( cpu >= nr_cpu_ids )
-            return -EBADSLT;
+            return -ENOTSOCK;
         on_selected_cpus(cpumask_of(cpu), do_write_l3_cbm, &info, 1);
     }
 
@@ -383,7 +383,7 @@ int psr_set_l3_cbm(struct domain *d, unsigned int socket, uint64_t cbm)
     if ( !found )
     {
         spin_unlock(&info->cbm_lock);
-        return -EUSERS;
+        return -EOVERFLOW;
     }
 
     cos = found - map;
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 8efef5c179..791166b06c 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -900,7 +900,7 @@ int vcpu_pause_by_systemcontroller(struct vcpu *v)
         new = old + 1;
 
         if ( new > 255 )
-            return -EUSERS;
+            return -EOVERFLOW;
 
         prev = cmpxchg(&v->controller_pause_count, old, new);
     } while ( prev != old );
@@ -980,7 +980,7 @@ int __domain_pause_by_systemcontroller(struct domain *d,
          * toolstack overflowing d->pause_count with many repeated hypercalls.
          */
         if ( new > 255 )
-            return -EUSERS;
+            return -EOVERFLOW;
 
         prev = cmpxchg(&d->controller_pause_count, old, new);
     } while ( prev != old );
diff --git a/xen/common/hvm/save.c b/xen/common/hvm/save.c
index da6e668982..c9882e5783 100644
--- a/xen/common/hvm/save.c
+++ b/xen/common/hvm/save.c
@@ -114,7 +114,7 @@ int hvm_save_one(struct domain *d, uint16_t typecode, uint16_t instance,
         uint32_t off;
         const struct hvm_save_descriptor *desc;
 
-        rv = -EBADSLT;
+        rv = -ENOENT;
         for ( off = 0; off < (ctxt.cur - sizeof(*desc)); off += desc->length )
         {
             desc = (void *)(ctxt.data + off);
diff --git a/xen/include/public/errno.h b/xen/include/public/errno.h
index 9a7e41110f..8c88bb1d40 100644
--- a/xen/include/public/errno.h
+++ b/xen/include/public/errno.h
@@ -21,6 +21,12 @@ enum xen_errno {
 /*
  * Values originating from x86 Linux. Please consider using respective
  * values when adding new definitions here.
+ *
+ * The set of identifiers to be added here shouldn't extend beyond what
+ * POSIX mandates (see e.g.
+ * http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/errno.h.html)
+ * with the exception that we support some optional (XSR) values
+ * specified there (but no new ones should be added).
  */
 
 XEN_ERRNO(EPERM,	 1)	/* Operation not permitted */
@@ -54,8 +60,6 @@ XEN_ERRNO(EDEADLK,	35)	/* Resource deadlock would occur */
 XEN_ERRNO(ENAMETOOLONG,	36)	/* File name too long */
 XEN_ERRNO(ENOLCK,	37)	/* No record locks available */
 XEN_ERRNO(ENOSYS,	38)	/* Function not implemented */
-XEN_ERRNO(EBADRQC,	56)	/* Invalid request code */
-XEN_ERRNO(EBADSLT,	57)	/* Invalid slot */
 XEN_ERRNO(ENODATA,	61)	/* No data available */
 XEN_ERRNO(ETIME,	62)	/* Timer expired */
 XEN_ERRNO(EBADMSG,	74)	/* Not a data message */
@@ -64,15 +68,13 @@ XEN_ERRNO(EILSEQ,	84)	/* Illegal byte sequence */
 #ifdef __XEN__ /* Internal only, should never be exposed to the guest. */
 XEN_ERRNO(ERESTART,	85)	/* Interrupted system call should be restarted */
 #endif
-XEN_ERRNO(EUSERS,	87)	/* Too many users */
+XEN_ERRNO(ENOTSOCK,	88)	/* Socket operation on non-socket */
 XEN_ERRNO(EOPNOTSUPP,	95)	/* Operation not supported on transport endpoint */
 XEN_ERRNO(EADDRINUSE,	98)	/* Address already in use */
 XEN_ERRNO(EADDRNOTAVAIL, 99)	/* Cannot assign requested address */
 XEN_ERRNO(ENOBUFS,	105)	/* No buffer space available */
 XEN_ERRNO(EISCONN,	106)	/* Transport endpoint is already connected */
 XEN_ERRNO(ENOTCONN,	107)	/* Transport endpoint is not connected */
-XEN_ERRNO(ESHUTDOWN,	108)	/* Cannot send after transport endpoint shutdown */
-XEN_ERRNO(ETOOMANYREFS,	109)	/* Too many references: cannot splice */
 XEN_ERRNO(ETIMEDOUT,	110)	/* Connection timed out */
 
 #undef XEN_ERRNO