x86/cpufeatures: Add FEATURE_ZEN

Add a ZEN feature bit so family-dependent static_cpu_has() optimizations
can be built for ZEN.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

CVE-2018-3639 (x86)

(backported from commit d1035d97)
[smb: adapted to set feature in the right place]
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

arch/x86/include/asm/cpufeatures.h

@@ -209,6 +209,7 @@
 #define X86_FEATURE_IBRS		( 7*32+25) /* Indirect Branch Restricted Speculation */
 #define X86_FEATURE_IBPB		( 7*32+26) /* Indirect Branch Prediction Barrier */
 #define X86_FEATURE_STIBP		( 7*32+27) /* Single Thread Indirect Branch Predictors */
+#define X86_FEATURE_ZEN			( 7*32+28) /* "" CPU is AMD family 0x17 (Zen) */
 
 /* Because the ALTERNATIVE scheme is for members of the X86_FEATURE club... */
 #define X86_FEATURE_KAISER		( 7*32+31) /* CONFIG_PAGE_TABLE_ISOLATION w/o nokaiser */

arch/x86/kernel/cpu/amd.c

@@ -806,6 +806,7 @@ static void init_amd(struct cpuinfo_x86 *c)
 		set_cpu_bug(c, X86_BUG_AMD_APIC_C1E);
 
 	if (c->x86 == 0x17) {
+		set_cpu_cap(c, X86_FEATURE_ZEN);
 		/*
 		 * Fix erratum 1076: CPB feature bit not being set in CPUID.
 		 * It affects all up to and including B1.