linux-kernel - [PATCH v2] x86/AMD: Fix Socket ID for LLC topology for AMD Fam17h systems

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Date:   Fri, 2 Sep 2016 20:40:48 -0500
From:   Yazen Ghannam <Yazen.Ghannam@....com>
To:     <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
        <x86@...nel.org>
CC:     <bp@...e.de>, <linux-kernel@...r.kernel.org>,
        Yazen Ghannam <Yazen.Ghannam@....com>
Subject: [PATCH v2] x86/AMD: Fix Socket ID for LLC topology for AMD Fam17h systems

Socket ID is an unsigned value and starts at 0. Subtracting 1
from it is incorrect and the result will underflow if
socket_id=0.

Remove substraction when extracting socket_id from c->apicid.

Signed-off-by: Yazen Ghannam <Yazen.Ghannam@....com>
---
Link:
http://lkml.kernel.org/r/1472674900-60688-1-git-send-email-Yazen.Ghannam@amd.com

v1->v2:
* Don't do logical AND so as to not restrict # of sockets to 2.

 arch/x86/kernel/cpu/amd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index f3d8a92..793bc23 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -365,7 +365,7 @@ static void amd_detect_cmp(struct cpuinfo_x86 *c)
 	 if (c->x86 != 0x17 || !cpuid_edx(0x80000006))
 		return;
 
-	socket_id	= (c->apicid >> bits) - 1;
+	socket_id	= c->apicid >> bits;
 	core_complex_id	= (c->apicid & ((1 << bits) - 1)) >> 3;
 
 	per_cpu(cpu_llc_id, cpu) = (socket_id << 3) | core_complex_id;
-- 
1.9.1