x86/topology: Set x86_max_cores to 1 for CONFIG_SMP=n

KAGA-KOKO · KAGA-KOKO · commit 8d415ee225a3 · 2016-05-10T09:28:31.000+02:00
Josef reported that the uncore driver trips over with CONFIG_SMP=n because x86_max_cores is 16 instead of 12. The reason is, that for SMP=n the extended topology detection is a NOOP and the cache leaf is used to determine the number of cores. That's wrong in two aspects: 1) The cache leaf enumerates the maximum addressable number of cores in the package, which is obviously not correct 2) UP has no business with topology bits at all. Make intel_num_cpu_cores() return 1 for CONFIG_SMP=n Reported-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: kernel-team <Kernel-team@fb.com> Cc: Kan Liang <kan.liang@intel.com> Link: http://lkml.kernel.org/r/761b4a2a-0332-7954-f030-c6639f949612@fb.com
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
@@ -336,7 +336,7 @@ static int intel_num_cpu_cores(struct cpuinfo_x86 *c)
 {
 	unsigned int eax, ebx, ecx, edx;
 
-	if (c->cpuid_level < 4)
+	if (!IS_ENABLED(CONFIG_SMP) || c->cpuid_level < 4)
 		return 1;
 
 	/* Intel has a non-standard dependency on %ecx for this CPUID level. */

Original file line number	Diff line number	Diff line change
`@@ -336,7 +336,7 @@ static int intel_num_cpu_cores(struct cpuinfo_x86 *c)`
`336`	`336`	`{`
`337`	`337`	`unsigned int eax, ebx, ecx, edx;`
`338`	`338`
`339`		`- if (c->cpuid_level < 4)`
	`339`	`+ if (!IS_ENABLED(CONFIG_SMP) \|\| c->cpuid_level < 4)`
`340`	`340`	`return 1;`
`341`	`341`
`342`	`342`	`/* Intel has a non-standard dependency on %ecx for this CPUID level. */`