x86, ptrace: PEBS support

Polish the ds.h interface and add support for PEBS.

Ds.c is meant to be the resource allocator for per-thread and per-cpu
BTS and PEBS recording.
It is used by ptrace/utrace to provide execution tracing of debugged tasks.
It will be used by profilers (e.g. perfmon2).
It may be used by kernel debuggers to provide a kernel execution trace.

Changes in detail:
- guard DS and ptrace by CONFIG macros
- separate DS and BTS more clearly
- simplify field accesses
- add functions to manage PEBS buffers
- add simple protection/allocation mechanism
- added support for Atom

Opens:
- buffer overflow handling
  Currently, only circular buffers are supported. This is all we need
  for debugging. Profilers would want an overflow notification.
  This is planned to be added when perfmon2 is made to use the ds.h
  interface.
- utrace intermediate layer

Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/Kconfig.cpu

@@ -415,3 +415,21 @@ config X86_MINIMUM_CPU_FAMILY
 config X86_DEBUGCTLMSR
 	def_bool y
 	depends on !(M586MMX || M586TSC || M586 || M486 || M386)
+
+config X86_DS
+	bool "Debug Store support"
+	default y
+	help
+	  Add support for Debug Store.
+	  This allows the kernel to provide a memory buffer to the hardware
+	  to store various profiling and tracing events.
+
+config X86_PTRACE_BTS
+	bool "ptrace interface to Branch Trace Store"
+	default y
+	depends on (X86_DS && X86_DEBUGCTLMSR)
+	help
+	  Add a ptrace interface to allow collecting an execution trace
+	  of the traced task.
+	  This collects control flow changes in a (cyclic) buffer and allows
+	  debuggers to fill in the gaps and show an execution trace of the debuggee.

arch/x86/kernel/cpu/intel.c

@@ -222,10 +222,11 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
 			set_cpu_cap(c, X86_FEATURE_BTS);
 		if (!(l1 & (1<<12)))
 			set_cpu_cap(c, X86_FEATURE_PEBS);
+		ds_init_intel(c);
 	}
 
 	if (cpu_has_bts)
-		ds_init_intel(c);
+		ptrace_bts_init_intel(c);
 }
 
 static unsigned int __cpuinit intel_size_cache(struct cpuinfo_x86 *c, unsigned int size)