x86/cpu/AMD: Evaluate smp_num_siblings early

To support force disabling of SMT it's required to know the number of
thread siblings early. amd_get_topology() cannot be called before the APIC
driver is selected, so split out the part which initializes
smp_num_siblings and invoke it from amd_early_init().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@kernel.org>

CVE-2018-3620
CVE-2018-3646
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

arch/x86/kernel/cpu/amd.c

@@ -291,6 +291,18 @@ static int nearby_node(int apicid)
 }
 #endif
 
+static void amd_get_topology_early(struct cpuinfo_x86 *c)
+{
+#ifdef CONFIG_SMP
+	if (boot_cpu_has(X86_FEATURE_TOPOEXT)) {
+		u32 eax, ebx, ecx, edx;
+
+		cpuid(0x8000001e, &eax, &ebx, &ecx, &edx);
+		smp_num_siblings = ((ebx >> 8) & 0xff) + 1;
+	}
+#endif
+}
+
 /*
  * Fixup core topology information for
  * (1) AMD multi-node processors
@@ -594,6 +606,8 @@ static void early_init_amd(struct cpuinfo_x86 *c)
 	/* F16h erratum 793, CVE-2013-6885 */
 	if (c->x86 == 0x16 && c->x86_model <= 0xf)
 		msr_set_bit(MSR_AMD64_LS_CFG, 15);
+
+	amd_get_topology_early(c);
 }
 
 static const int amd_erratum_383[];