linux-kernel - [tip:x86/urgent] x86/topology: Set x86_max_cores to 1 for CONFIG

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Date:	Tue, 10 May 2016 00:33:44 -0700
From:	tip-bot for Thomas Gleixner <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	Kernel-team@...com, tglx@...utronix.de, mingo@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, peterz@...radead.org,
	kan.liang@...el.com, jbacik@...com
Subject: [tip:x86/urgent] x86/topology: Set x86_max_cores to 1 for
 CONFIG_SMP=n

Commit-ID:  8d415ee225a3d15d3e3029524350e8237a4de7b8
Gitweb:     http://git.kernel.org/tip/8d415ee225a3d15d3e3029524350e8237a4de7b8
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Tue, 10 May 2016 09:20:33 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 10 May 2016 09:28:31 +0200

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

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@...com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: kernel-team <Kernel-team@...com>
Cc: Kan Liang <kan.liang@...el.com>
Link: http://lkml.kernel.org/r/761b4a2a-0332-7954-f030-c6639f949612@fb.com
---
 arch/x86/kernel/cpu/intel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 1f7fdb9..e4393bf 100644
--- 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. */