Commit b89b41d0 authored Jul 31, 2017 by Suravee Suthikulpanit Committed by Ingo Molnar Aug 10, 2017

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@amd.com>
[ Heavily massaged. ]
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yazen Ghannam <Yazen.Ghannam@amd.com>
Link: http://lkml.kernel.org/r/20170731085159.9455-2-bp@alien8.de


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 8d31f80e

arch/x86/kernel/cpu/amd.c

+17 −7

Original line number	Diff line number	Diff line
		@@ -297,6 +297,22 @@ 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
		@@ -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