x86/bugs: Fix SRSO reporting on Zen1/2 with SMT disabled

1f4bb06 ("x86/bugs: Restructure SRSO mitigation") does this:

  if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
          setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
          srso_mitigation = SRSO_MITIGATION_NONE;
          return;
  }

and, in particular, sets srso_mitigation to NONE. This leads to
reporting

  Speculative Return Stack Overflow: Vulnerable

on Zen2 machines.

There's a far bigger confusion with what SRSO_NO means and how it is
used in the code but this will be a matter of future fixes and
restructuring to how the SRSO mitigation gets determined.

Fix the reporting issue for now.

Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Reviewed-by: David Kaplan <[email protected]>
Link: https://lore.kernel.org/[email protected]

Author: bp3tk0v

arch/x86/kernel/cpu/bugs.c

@@ -2942,7 +2942,9 @@ static void __init srso_update_mitigation(void)
 	    boot_cpu_has(X86_FEATURE_IBPB_BRTYPE))
 		srso_mitigation = SRSO_MITIGATION_IBPB;
 
-	if (boot_cpu_has_bug(X86_BUG_SRSO) && !cpu_mitigations_off())
+	if (boot_cpu_has_bug(X86_BUG_SRSO) &&
+	    !cpu_mitigations_off() &&
+	    !boot_cpu_has(X86_FEATURE_SRSO_NO))
 		pr_info("%s\n", srso_strings[srso_mitigation]);
 }