[PATCH for-4.14] docs/ucode: Extend runtime microcode loading documentation

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Extend the disclaimer about runtime loading.  While we've done our best to
make the mechaism reliable, the safety of late loading does ultimately depend
on the contents of the blobs.

Extend the xen-ucode portion with examples of how to use it.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Julien Grall <julien@xxxxxxx>
CC: Paul Durrant <paul@xxxxxxx>
---
 docs/admin-guide/microcode-loading.rst | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/docs/admin-guide/microcode-loading.rst 
b/docs/admin-guide/microcode-loading.rst
index 5f0f661a2e..8cd5d0351b 100644
--- a/docs/admin-guide/microcode-loading.rst
+++ b/docs/admin-guide/microcode-loading.rst
@@ -104,8 +104,8 @@ modules to find any CPIO archives, and search the archive 
for the applicable
 file.  Xen will stop searching at the first match.
 
 
-Run time microcode loading
---------------------------
+Runtime microcode loading
+-------------------------
 
 .. warning::
 
@@ -113,7 +113,23 @@ Run time microcode loading
    or at boot time.  Not all microcode updates (or parts thereof) can be
    applied at runtime.
 
-The ``xen-ucode`` utility can be used to initiate a runtime microcode load.
+   Given the proprietry nature of microcode, we are unable to make any claim
+   that a runtime microcode is risk-free.  Any runtime microcode loading needs
+   adequate testing on a dev instance before being rolled out to production
+   systems.
+
+The ``xen-ucode`` utility can be used to initiate a runtime microcode load::
+
+  [root@host ~]# xen-ucode
+  xen-ucode: Xen microcode updating tool
+  Usage: xen-ucode <microcode blob>
+  [root@host ~]#
+
+e.g. With a Linux dom0 on a Haswell system::
+
+  [root@host ~]# xen-ucode /lib/firmware/intel-ucode/06-3c-03
+  [root@host ~]#
+
 It will pass the blob to Xen, which will check to see whether the blob is
 correct for the processor, and newer than the running microcode.
 
-- 
2.11.0