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

From: tip-bot for Suravee Suthikulpanit
Date: Thu Aug 10 2017 - 12:48:28 EST


Commit-ID: b89b41d0b8414690ec0030c134b8bde209e6d06c
Gitweb: http://git.kernel.org/tip/b89b41d0b8414690ec0030c134b8bde209e6d06c
Author: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
AuthorDate: Mon, 31 Jul 2017 10:51:58 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
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@xxxxxxx>
[ Heavily massaged. ]
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Yazen Ghannam <Yazen.Ghannam@xxxxxxx>
Link: http://lkml.kernel.org/r/20170731085159.9455-2-bp@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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