linux-kernel - [PATCH] x86, amd: Re-enable CPU topology extensions in case BIOS has disabled it

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Date:	Wed, 11 Apr 2012 17:26:40 +0200
From:	Andreas Herrmann <andreas.herrmann3@....com>
To:	Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	<linux-kernel@...r.kernel.org>
Subject: [PATCH] x86, amd: Re-enable CPU topology extensions in case BIOS has
 disabled it


For detection of thread siblings we are relying on the topology
extension CPUID leafs. Thus we have to re-enable it in case BIOS tries
to hide the correpsonding CPUID feature flag.

Cc: stable@...r.kernel.org
Signed-off-by: Andreas Herrmann <andreas.herrmann3@....com>
---
 arch/x86/kernel/cpu/amd.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 0a44b90..56a694b 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -579,6 +579,24 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
 		}
 	}
 
+	/* re-enable TopologyExtensions if switched off by BIOS */
+	if ((c->x86 == 0x15) &&
+	    (c->x86_model >= 0x10) && (c->x86_model <= 0x1f) &&
+	    !cpu_has(c, X86_FEATURE_TOPOEXT)) {
+		u64 val;
+
+		if (!rdmsrl_amd_safe(0xc0011005, &val)) {
+			val |= 1ULL << 54;
+			wrmsrl_amd_safe(0xc0011005, val);
+			rdmsrl(0xc0011005, val);
+			if (val & (1ULL << 54)) {
+				set_cpu_cap(c, X86_FEATURE_TOPOEXT);
+				printk(KERN_INFO FW_INFO "CPU: Re-enabling "
+				  "disabled Topology Extensions Support\n");
+			}
+		}
+	}
+
 	cpu_detect_cache_sizes(c);
 
 	/* Multi core CPU? */
-- 
1.7.5.rc3



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