x86/spec-ctrl: Use a taint for CET without MSR_SPEC_CTRL

Reword the comment for 'S' to include an incompatible set of features on the
same core.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit 3f63f45104)

xen/arch/x86/spec_ctrl.c

@@ -1139,7 +1139,10 @@ void __init init_speculation_mitigations(void)
     if ( read_cr4() & X86_CR4_CET )
     {
         if ( !has_spec_ctrl )
+        {
             printk(XENLOG_WARNING "?!? CET active, but no MSR_SPEC_CTRL?\n");
+            add_taint(TAINT_CPU_OUT_OF_SPEC);
+        }
         else if ( opt_ibrs == -1 )
             opt_ibrs = ibrs = true;
 

xen/common/kernel.c

@@ -339,7 +339,7 @@ unsigned int tainted;
  *  'H' - HVM forced emulation prefix is permitted.
  *  'M' - Machine had a machine check experience.
  *  'U' - Platform is unsecure (usually due to an errata on the platform).
- *  'S' - Out of spec CPU (One core has a feature incompatible with others).
+ *  'S' - Out of spec CPU (Incompatible features on one or more cores).
  *
  *      The string is overwritten by the next call to print_taint().
  */