Since modern kernels don't allow unprivileged processes to read the
pagemaps file, the instructions on running as non-root are out-of-date. Add
a note clarifying that they will only work with earlier kernel versions.

Signed-off-by: Bruce Richardson <bruce.richard...@intel.com>
---
 doc/guides/linux_gsg/enable_func.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/doc/guides/linux_gsg/enable_func.rst 
b/doc/guides/linux_gsg/enable_func.rst
index e6c806b0d..5ac0184a1 100644
--- a/doc/guides/linux_gsg/enable_func.rst
+++ b/doc/guides/linux_gsg/enable_func.rst
@@ -87,6 +87,14 @@ The application can then determine what action to take, if 
any, if the HPET is n
 Running DPDK Applications Without Root Privileges
 --------------------------------------------------------
 
+.. note::
+
+    The instructions below will allow running DPDK as non-root with older
+    Linux kernel versions. However, since version 4.0, the kernel does not 
allow
+    unprivileged processes to read the physical address information from
+    the pagemaps file, making it impossible for those processes to use HW
+    devices which require physical addresses
+
 Although applications using the DPDK use network ports and other hardware 
resources directly,
 with a number of small permission adjustments it is possible to run these 
applications as a user other than "root".
 To do so, the ownership, or permissions, on the following Linux file system 
objects should be adjusted to ensure that
-- 
2.13.3

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