linux-kernel - [tip:x86/cpu] x86/cpu/amd: Limit cpu_core

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Date:   Thu, 10 Aug 2017 09:42:36 -0700
From:   tip-bot for Suravee Suthikulpanit <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, bp@...e.de, linux-kernel@...r.kernel.org,
        mingo@...nel.org, tglx@...utronix.de,
        torvalds@...ux-foundation.org, peterz@...radead.org,
        Yazen.Ghannam@....com, suravee.suthikulpanit@....com
Subject: [tip:x86/cpu] x86/cpu/amd: Limit cpu_core_id fixup to families
 older than F17h

Commit-ID:  b89b41d0b8414690ec0030c134b8bde209e6d06c
Gitweb:     http://git.kernel.org/tip/b89b41d0b8414690ec0030c134b8bde209e6d06c
Author:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>
AuthorDate: Mon, 31 Jul 2017 10:51:58 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 10 Aug 2017 17:37:43 +0200

x86/cpu/amd: Limit cpu_core_id fixup to families older than F17h

Current cpu_core_id fixup causes downcored F17h configurations to be
incorrect:

  NODE: 0
  processor  0 core id : 0
  processor  1 core id : 1
  processor  2 core id : 2
  processor  3 core id : 4
  processor  4 core id : 5
  processor  5 core id : 0

  NODE: 1
  processor  6 core id : 2
  processor  7 core id : 3
  processor  8 core id : 4
  processor  9 core id : 0
  processor 10 core id : 1
  processor 11 core id : 2

Code that relies on the cpu_core_id, like match_smt(), for example,
which builds the thread siblings masks used by the scheduler, is
mislead.

So, limit the fixup to pre-F17h machines. The new value for cpu_core_id
for F17h and later will represent the CPUID_Fn8000001E_EBX[CoreId],
which is guaranteed to be unique for each core within a socket.

This way we have:

  NODE: 0
  processor  0 core id : 0
  processor  1 core id : 1
  processor  2 core id : 2
  processor  3 core id : 4
  processor  4 core id : 5
  processor  5 core id : 6

  NODE: 1
  processor  6 core id : 8
  processor  7 core id : 9
  processor  8 core id : 10
  processor  9 core id : 12
  processor 10 core id : 13
  processor 11 core id : 14

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
[ Heavily massaged. ]
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Yazen Ghannam <Yazen.Ghannam@....com>
Link: http://lkml.kernel.org/r/20170731085159.9455-2-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/cpu/amd.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 3b9e220..82d571c 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -298,6 +298,22 @@ static int nearby_node(int apicid)
 #endif
 
 /*
+ * Fix up cpu_core_id for pre-F17h systems to be in the
+ * [0 .. cores_per_node - 1] range. Not really needed but
+ * kept so as not to break existing setups.
+ */
+static void legacy_fixup_core_id(struct cpuinfo_x86 *c)
+{
+	u32 cus_per_node;
+
+	if (c->x86 >= 0x17)
+		return;
+
+	cus_per_node = c->x86_max_cores / nodes_per_socket;
+	c->cpu_core_id %= cus_per_node;
+}
+
+/*
  * Fixup core topology information for
  * (1) AMD multi-node processors
  *     Assumption: Number of cores in each internal node is the same.
@@ -354,15 +370,9 @@ static void amd_get_topology(struct cpuinfo_x86 *c)
 	} else
 		return;
 
-	/* fixup multi-node processor information */
 	if (nodes_per_socket > 1) {
-		u32 cus_per_node;
-
 		set_cpu_cap(c, X86_FEATURE_AMD_DCM);
-		cus_per_node = c->x86_max_cores / nodes_per_socket;
-
-		/* core id has to be in the [0 .. cores_per_node - 1] range */
-		c->cpu_core_id %= cus_per_node;
+		legacy_fixup_core_id(c);
 	}
 }
 #endif