[PATCH] [85/139] x86, amd: Fix panic on AMD CPU family 0x15

[Andi Kleen]

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Andreas Herrmann <andreas.herrmann3@xxxxxxx>

[The mainline kernel doesn't have this problem. Commit "(23588c3) x86,
amd: Add support for CPUID topology extension of AMD CPUs" removed the
family check. But 2.6.32.y needs to be fixed.]

This CPU family check is not required -- existence of the NodeId MSR
is indicated by a CPUID feature flag which is already checked in
amd_fixup_dcm() -- and it needlessly prevents amd_fixup_dcm() to be
called for newer AMD CPUs.

In worst case this can lead to a panic in the scheduler code for AMD
family 0x15 multi-node AMD CPUs. I just have a picture of VGA console
output so I can't copy-and-paste it herein, but the call stack of such
a panic looked like:

  do_divide_error
  ...
  find_busiest_group
  run_rebalance_domains
  ...
  apic_timer_interrupt
  ...
  cpu_idle

The mainline kernel doesn't have this problem. Commit "(23588c3) x86,
amd: Add support for CPUID topology extension of AMD CPUs" removed the
family check. But 2.6.32.y needs to be fixed.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>

---
 arch/x86/kernel/cpu/amd.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Index: linux-2.6.35.y/arch/x86/kernel/cpu/amd.c
===================================================================
--- linux-2.6.35.y.orig/arch/x86/kernel/cpu/amd.c
+++ linux-2.6.35.y/arch/x86/kernel/cpu/amd.c
@@ -305,8 +305,7 @@ static void __cpuinit amd_detect_cmp(str
 	/* use socket ID also for last level cache */
 	per_cpu(cpu_llc_id, cpu) = c->phys_proc_id;
 	/* fixup topology information on multi-node processors */
-	if ((c->x86 == 0x10) && (c->x86_model == 9))
-		amd_fixup_dcm(c);
+	amd_fixup_dcm(c);
 #endif
 }
 
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