UBUNTU: SAUCE: x86/pti: Evaluate X86_BUG_CPU_MELTDOWN when pti=auto

CVE-2018-3639 (x86)

Commit f93e1bcd ("x86/pti: Do not enable PTI on CPUs which are not
vulnerable to Meltdown") introduced a smarter detection of CPUs that
are not affected by Meltdown. Make use of that when pti=auto which also
matches Linus' tree.

While at it, remove the unused variable 'enable'.
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>

arch/x86/mm/kaiser.c

@@ -278,7 +278,6 @@ static void __init kaiser_init_all_pgds(void)
 
 void __init kaiser_check_boottime_disable(void)
 {
-	bool enable = true;
 	char arg[5];
 	int ret;
 
@@ -301,13 +300,11 @@ void __init kaiser_check_boottime_disable(void)
 		goto disable;
 
 skip:
-	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
+	if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
 		goto disable;
 
 enable:
-	if (enable)
-		setup_force_cpu_cap(X86_FEATURE_KAISER);
-
+	setup_force_cpu_cap(X86_FEATURE_KAISER);
 	return;
 
 disable: