man/systemd-detect-virt: list known CVM technologies

Add a section which lists the known confidential virtual machine
technologies.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
(cherry picked from commit a8fb5d2)

Related: RHEL-56144

man/systemd-detect-virt.xml

@@ -217,6 +217,50 @@
     WSL is categorized as a container for practical purposes.
     Multiple WSL environments share the same kernel and services
     should generally behave like when being run in a container.</para>
+
+    <para>When executed with <option>--cvm</option>, instead of
+    printing the virtualization technology, it will display the
+    confidential virtual machine technology, if any. The
+    following technologies are currently identified:</para>
+
+    <table>
+      <title>Known confidential virtualization technologies</title>
+      <tgroup cols='2' align='left' colsep='1' rowsep='1'>
+        <colspec colname="id" />
+        <colspec colname="product" />
+        <thead>
+          <row>
+            <entry>Arch</entry>
+            <entry>ID</entry>
+            <entry>Technology</entry>
+          </row>
+        </thead>
+        <tbody>
+          <row>
+            <entry valign="top" morerows="3">x86_64</entry>
+            <entry><varname>sev</varname></entry>
+            <entry>AMD Secure Encrypted Virtualization</entry>
+          </row>
+          <row>
+            <entry><varname>sev-es</varname></entry>
+            <entry>AMD Secure Encrypted Virtualization - Encrypted State</entry>
+          </row>
+          <row>
+            <entry><varname>sev-snp</varname></entry>
+            <entry>AMD Secure Encrypted Virtualization - Secure Nested Paging</entry>
+          </row>
+          <row>
+            <entry><varname>tdx</varname></entry>
+            <entry>Intel Trust Domain Extensions</entry>
+          </row>
+          <row>
+            <entry>s390x</entry>
+            <entry><varname>protvirt</varname></entry>
+            <entry>IBM Protected Virtualization (Secure Execution)</entry>
+          </row>
+        </tbody>
+      </tgroup>
+    </table>
   </refsect1>
 
   <refsect1>