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>

1 files changed, 21 insertions, 4 deletions

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index e2319f39988..ad213494a22 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -267,6 +267,14 @@ void exit_thread(void)
                 t->io_bitmap_max = 0;
                 put_cpu();
         }
+#ifdef CONFIG_X86_DS
+        /* Free any DS contexts that have not been properly released. */
+        if (unlikely(t->ds_ctx)) {
+                /* we clear debugctl to make sure DS is not used. */
+                update_debugctlmsr(0);
+                ds_free(t->ds_ctx);
+        }
+#endif /* CONFIG_X86_DS */
 }
 
 void flush_thread(void)
@@ -492,18 +500,27 @@ static inline void __switch_to_xtra(struct task_struct *prev_p,
 {
         struct thread_struct *prev, *next;
         unsigned long debugctl;
+        unsigned long ds_prev = 0, ds_next = 0;
 
         prev = &prev_p->thread,
         next = &next_p->thread;
 
         debugctl = prev->debugctlmsr;
-        if (next->ds_area_msr != prev->ds_area_msr) {
+
+#ifdef CONFIG_X86_DS
+        if (prev->ds_ctx)
+                ds_prev = (unsigned long)prev->ds_ctx->ds;
+        if (next->ds_ctx)
+                ds_next = (unsigned long)next->ds_ctx->ds;
+
+        if (ds_next != ds_prev) {
                 /* we clear debugctl to make sure DS
                  * is not in use when we change it */
                 debugctl = 0;
                 update_debugctlmsr(0);
-                wrmsrl(MSR_IA32_DS_AREA, next->ds_area_msr);
+                wrmsrl(MSR_IA32_DS_AREA, ds_next);
         }
+#endif /* CONFIG_X86_DS */
 
         if (next->debugctlmsr != debugctl)
                 update_debugctlmsr(next->debugctlmsr);
@@ -541,13 +558,13 @@ static inline void __switch_to_xtra(struct task_struct *prev_p,
                 memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
         }
 
-#ifdef X86_BTS
+#ifdef CONFIG_X86_PTRACE_BTS
         if (test_tsk_thread_flag(prev_p, TIF_BTS_TRACE_TS))
                 ptrace_bts_take_timestamp(prev_p, BTS_TASK_DEPARTS);
 
         if (test_tsk_thread_flag(next_p, TIF_BTS_TRACE_TS))
                 ptrace_bts_take_timestamp(next_p, BTS_TASK_ARRIVES);
-#endif
+#endif /* CONFIG_X86_PTRACE_BTS */
 }
 
 /*