linux-kernel - [PATCH] x86/CPU/AMD: Fix Bulldozer topology

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Date:   Thu,  5 Jan 2017 10:26:38 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     Brice Goglin <Brice.Goglin@...ia.fr>,
        Yazen Ghannam <yazen.ghannam@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/CPU/AMD: Fix Bulldozer topology

From: Borislav Petkov <bp@...e.de>

8196dab4fc15 ("x86/cpu: Get rid of compute_unit_id") broke the initial
strategy for Bulldozer-based cores' topology, where we consider each
thread of a compute unit a standalone core and not a HT or SMT thread.

Revert to the firmware-supplied core_id numbering and do not make
them thread siblings as we don't consider them for such even if they
technically are, more or less.

Reported-and-tested-by: Brice Goglin <Brice.Goglin@...ia.fr>
Tested-by: Yazen Ghannam <yazen.ghannam@....com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: <stable@...r.kernel.org> # v4.6..
Fixes: 8196dab4fc15 ("x86/cpu: Get rid of compute_unit_id")
---
 arch/x86/kernel/cpu/amd.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 71cae73a5076..1d3167269a67 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -309,15 +309,8 @@ static void amd_get_topology(struct cpuinfo_x86 *c)
 
 	/* get information required for multi-node processors */
 	if (boot_cpu_has(X86_FEATURE_TOPOEXT)) {
-		u32 eax, ebx, ecx, edx;
 
-		cpuid(0x8000001e, &eax, &ebx, &ecx, &edx);
-		node_id = ecx & 7;
-
-		/* get compute unit information */
-		smp_num_siblings = ((ebx >> 8) & 3) + 1;
-		c->x86_max_cores /= smp_num_siblings;
-		c->cpu_core_id = ebx & 0xff;
+		node_id = cpuid_ecx(0x8000001e) & 7;
 
 		/*
 		 * We may have multiple LLCs if L3 caches exist, so check if we
-- 
2.11.0