x86/speculation: Fix redundant MDS mitigation message

commit cd5a2aa89e847bdda7b62029d94e95488d73f6b2 upstream.

Since MDS and TAA mitigations are inter-related for processors that are
affected by both vulnerabilities, the followiing confusing messages can
be printed in the kernel log:

  MDS: Vulnerable
  MDS: Mitigation: Clear CPU buffers

To avoid the first incorrect message, defer the printing of MDS
mitigation after the TAA mitigation selection has been done. However,
that has the side effect of printing TAA mitigation first before MDS
mitigation.

 [ bp: Check box is affected/mitigations are disabled first before
   printing and massage. ]
Suggested-by: NPawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: NWaiman Long <longman@redhat.com>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Mark Gross <mgross@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20191115161445.30809-3-longman@redhat.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/kernel/cpu/bugs.c

@@ -39,6 +39,7 @@ static void __init spectre_v2_select_mitigation(void);
 static void __init ssb_select_mitigation(void);
 static void __init l1tf_select_mitigation(void);
 static void __init mds_select_mitigation(void);
+static void __init mds_print_mitigation(void);
 static void __init taa_select_mitigation(void);
 
 /* The base value of the SPEC_CTRL MSR that always has to be preserved. */
@@ -108,6 +109,12 @@ void __init check_bugs(void)
 	mds_select_mitigation();
 	taa_select_mitigation();
 
+	/*
+	 * As MDS and TAA mitigations are inter-related, print MDS
+	 * mitigation until after TAA mitigation selection is done.
+	 */
+	mds_print_mitigation();
+
 	arch_smt_update();
 
 #ifdef CONFIG_X86_32
@@ -245,6 +252,12 @@ static void __init mds_select_mitigation(void)
 		    (mds_nosmt || cpu_mitigations_auto_nosmt()))
 			cpu_smt_disable(false);
 	}
+}
+
+static void __init mds_print_mitigation(void)
+{
+	if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off())
+		return;
 
 	pr_info("%s\n", mds_strings[mds_mitigation]);
 }