diff --git a/opal/mca/btl/vader/btl_vader.h b/opal/mca/btl/vader/btl_vader.h
index 028c7a3816..eab5f5a87d 100644
--- a/opal/mca/btl/vader/btl_vader.h
+++ b/opal/mca/btl/vader/btl_vader.h
@@ -84,7 +84,12 @@ union vader_modex_t {
         void *segment_base;
     } xpmem;
 #endif
-    opal_shmem_ds_t seg_ds;
+    struct vader_modex_other_t {
+        ino_t user_ns_id;
+        int seg_ds_size;
+        /* seg_ds needs to be the last element */
+        opal_shmem_ds_t seg_ds;
+    } other;
 };
 
 /**
@@ -270,6 +275,8 @@ int mca_btl_vader_get_knem (mca_btl_base_module_t *btl, mca_btl_base_endpoint_t
                             int order, mca_btl_base_rdma_completion_fn_t cbfunc, void *cbcontext, void *cbdata);
 #endif
 
+ino_t mca_btl_vader_get_user_ns_id(void);
+
 int mca_btl_vader_get_sc_emu (mca_btl_base_module_t *btl, mca_btl_base_endpoint_t *endpoint, void *local_address,
                                uint64_t remote_address, mca_btl_base_registration_handle_t *local_handle,
                                mca_btl_base_registration_handle_t *remote_handle, size_t size, int flags,
diff --git a/opal/mca/btl/vader/btl_vader_component.c b/opal/mca/btl/vader/btl_vader_component.c
index 98ac462b71..44de7e004c 100644
--- a/opal/mca/btl/vader/btl_vader_component.c
+++ b/opal/mca/btl/vader/btl_vader_component.c
@@ -41,6 +41,10 @@
 #include "btl_vader_fbox.h"
 #include "btl_vader_xpmem.h"
 
+#ifdef HAVE_SYS_STAT_H
+#include <sys/stat.h>
+#endif
+
 #include <sys/mman.h>
 #include <fcntl.h>
 
@@ -350,6 +354,25 @@ static int mca_btl_vader_component_close(void)
     return OPAL_SUCCESS;
 }
 
+/*
+ * mca_btl_vader_parse_proc_ns_user() tries to get the user namespace ID
+ * of the current process.
+ * Returns the ID of the user namespace. In the case of an error '0' is returned.
+ */
+ino_t mca_btl_vader_get_user_ns_id(void)
+{
+    struct stat buf;
+
+    if (0 > stat("/proc/self/ns/user", &buf)) {
+        /*
+         * Something went wrong, probably an old kernel that does not support namespaces
+         * simply assume all processes are in the same user namespace and return 0
+         */
+        return 0;
+    }
+
+    return buf.st_ino;
+}
 static int mca_btl_base_vader_modex_send (void)
 {
     union vader_modex_t modex;
@@ -363,8 +386,16 @@ static int mca_btl_base_vader_modex_send (void)
         modex_size = sizeof (modex.xpmem);
     } else {
 #endif
-        modex_size = opal_shmem_sizeof_shmem_ds (&mca_btl_vader_component.seg_ds);
-        memmove (&modex.seg_ds, &mca_btl_vader_component.seg_ds, modex_size);
+        modex.other.seg_ds_size = opal_shmem_sizeof_shmem_ds (&mca_btl_vader_component.seg_ds);
+        memmove (&modex.other.seg_ds, &mca_btl_vader_component.seg_ds, modex.other.seg_ds_size);
+        modex.other.user_ns_id = mca_btl_vader_get_user_ns_id();
+        /*
+         * If modex.other.user_ns_id is '0' something did not work out
+         * during user namespace detection. Assuming there are no
+         * namespaces available it will return '0' for all processes and
+         * the check later will see '0' everywhere and not disable CMA.
+         */
+        modex_size = sizeof (modex.other);
 
 #if OPAL_BTL_VADER_HAVE_XPMEM
     }
diff --git a/opal/mca/btl/vader/btl_vader_module.c b/opal/mca/btl/vader/btl_vader_module.c
index a1cd167e22..e54c02b569 100644
--- a/opal/mca/btl/vader/btl_vader_module.c
+++ b/opal/mca/btl/vader/btl_vader_module.c
@@ -27,6 +27,7 @@
  */
 
 #include "opal_config.h"
+#include "opal/util/show_help.h"
 
 #include "btl_vader.h"
 #include "btl_vader_endpoint.h"
@@ -79,6 +80,28 @@ mca_btl_vader_t mca_btl_vader = {
     }
 };
 
+/*
+ * Exit function copied from btl_usnic_util.c
+ *
+ * The following comment tells Coverity that this function does not return.
+ * See https://scan.coverity.com/tune.
+ */
+
+/* coverity[+kill] */
+static void vader_btl_exit(mca_btl_vader_t *btl)
+{
+    if (NULL != btl && NULL != btl->error_cb) {
+        btl->error_cb(&btl->super, MCA_BTL_ERROR_FLAGS_FATAL,
+                      (opal_proc_t*) opal_proc_local_get(),
+                      "The vader BTL is aborting the MPI job (via PML error callback).");
+    }
+
+    /* If the PML error callback returns (or if there wasn't one), just exit. Shrug. */
+    fprintf(stderr, "*** The Open MPI vader BTL is aborting the MPI job (via exit(3)).\n");
+    fflush(stderr);
+    exit(1);
+}
+
 static int vader_btl_first_time_init(mca_btl_vader_t *vader_btl, int n)
 {
     mca_btl_vader_component_t *component = &mca_btl_vader_component;
@@ -173,6 +196,7 @@ static int vader_btl_first_time_init(mca_btl_vader_t *vader_btl, int n)
 static int init_vader_endpoint (struct mca_btl_base_endpoint_t *ep, struct opal_proc_t *proc, int remote_rank) {
     mca_btl_vader_component_t *component = &mca_btl_vader_component;
     union vader_modex_t *modex;
+    ino_t my_user_ns_id;
     size_t msg_size;
     int rc;
 
@@ -197,17 +221,58 @@ static int init_vader_endpoint (struct mca_btl_base_endpoint_t *ep, struct opal_
         } else {
 #endif
             /* store a copy of the segment information for detach */
-            ep->segment_data.other.seg_ds = malloc (msg_size);
+            ep->segment_data.other.seg_ds = malloc (modex->other.seg_ds_size);
             if (NULL == ep->segment_data.other.seg_ds) {
                 return OPAL_ERR_OUT_OF_RESOURCE;
             }
 
-            memcpy (ep->segment_data.other.seg_ds, &modex->seg_ds, msg_size);
+            memcpy (ep->segment_data.other.seg_ds, &modex->other.seg_ds, modex->other.seg_ds_size);
 
             ep->segment_base = opal_shmem_segment_attach (ep->segment_data.other.seg_ds);
             if (NULL == ep->segment_base) {
                 return OPAL_ERROR;
             }
+
+            if (MCA_BTL_VADER_CMA == mca_btl_vader_component.single_copy_mechanism) {
+                my_user_ns_id = mca_btl_vader_get_user_ns_id();
+                if (my_user_ns_id != modex->other.user_ns_id) {
+                    mca_base_var_source_t source;
+                    int vari;
+                    rc = mca_base_var_find_by_name("btl_vader_single_copy_mechanism", &vari);
+                    if (OPAL_ERROR == rc) {
+                        return OPAL_ERROR;
+                    }
+                    rc = mca_base_var_get_value(vari, NULL, &source, NULL);
+                    if (OPAL_ERROR == rc) {
+                        return OPAL_ERROR;
+                    }
+                    /*
+                     * CMA is not possible as different user namespaces are in use.
+                     * Currently the kernel does not allow * process_vm_{read,write}v()
+                     * for processes running in different user namespaces even if
+                     * all involved user IDs are mapped to the same user ID.
+                     *
+                     * Fallback to MCA_BTL_VADER_EMUL.
+                     */
+                    if (MCA_BASE_VAR_SOURCE_DEFAULT != source) {
+                        /* If CMA has been explicitly selected we want to error out */
+                        opal_show_help("help-btl-vader.txt", "cma-different-user-namespace-error",
+                                       true, opal_process_info.nodename);
+                        vader_btl_exit(&mca_btl_vader);
+                    }
+                    /*
+                     * If CMA has been selected because it is the default or
+                     * some fallback, this falls back even further.
+                     */
+                    opal_show_help("help-btl-vader.txt", "cma-different-user-namespace-warning",
+                                   true, opal_process_info.nodename);
+                    mca_btl_vader_component.single_copy_mechanism = MCA_BTL_VADER_EMUL;
+                    mca_btl_vader.super.btl_get = mca_btl_vader_get_sc_emu;
+                    mca_btl_vader.super.btl_put = mca_btl_vader_put_sc_emu;
+                    mca_btl_vader.super.btl_put_limit = mca_btl_vader.super.btl_max_send_size - sizeof (mca_btl_vader_sc_emu_hdr_t);
+                    mca_btl_vader.super.btl_get_limit = mca_btl_vader.super.btl_max_send_size - sizeof (mca_btl_vader_sc_emu_hdr_t);
+                }
+            }
 #if OPAL_BTL_VADER_HAVE_XPMEM
         }
 #endif
diff --git a/opal/mca/btl/vader/help-btl-vader.txt b/opal/mca/btl/vader/help-btl-vader.txt
index 9d87267564..ea87559d45 100644
--- a/opal/mca/btl/vader/help-btl-vader.txt
+++ b/opal/mca/btl/vader/help-btl-vader.txt
@@ -121,6 +121,25 @@ WARNING: Linux kernel CMA support was requested via the
 btl_vader_single_copy_mechanism MCA variable, but CMA support is
 not available due to restrictive ptrace settings.
 
+The vader shared memory BTL will fall back on another single-copy
+mechanism if one is available. This may result in lower performance.
+
+  Local host: %s
+#
+[cma-different-user-namespace-error]
+ERROR: Linux kernel CMA support was requested via the
+btl_vader_single_copy_mechanism MCA variable, but CMA support is
+not available due to different user namespaces.
+
+Your MPI job will abort now. Please select another value for
+btl_vader_single_copy_mechanism.
+
+  Local host: %s
+#
+[cma-different-user-namespace-warning]
+WARNING: The default btl_vader_single_copy_mechanism CMA is
+not available due to different user namespaces.
+
 The vader shared memory BTL will fall back on another single-copy
 mechanism if one is available. This may result in lower performance.