x86, ptrace: support for branch trace store(BTS)

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Changes to the last version:
- split implementation into two layers: ds/bts and ptrace
- renamed TIF's
- save/restore ds save area msr in __switch_to_xtra()
- make block-stepping only look at BTF bit

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

1 files changed, 23 insertions, 3 deletions

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 057b5442ffda..843bf0c978a4 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -568,11 +568,21 @@ static inline void __switch_to_xtra(struct task_struct *prev_p,
                                     struct tss_struct *tss)
 {
         struct thread_struct *prev, *next;
+        unsigned long debugctl;
 
         prev = &prev_p->thread,
         next = &next_p->thread;
 
-        if (next->debugctlmsr != prev->debugctlmsr)
+        debugctl = prev->debugctlmsr;
+        if (next->ds_area_msr != prev->ds_area_msr) {
+                /* we clear debugctl to make sure DS
+                 * is not in use when we change it */
+                debugctl = 0;
+                wrmsrl(MSR_IA32_DEBUGCTLMSR, 0);
+                wrmsrl(MSR_IA32_DS_AREA, next->ds_area_msr);
+        }
+
+        if (next->debugctlmsr != debugctl)
                 wrmsrl(MSR_IA32_DEBUGCTLMSR, next->debugctlmsr);
 
         if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
@@ -598,6 +608,16 @@ static inline void __switch_to_xtra(struct task_struct *prev_p,
                  */
                 memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
         }
+
+        /*
+         * Last branch recording recofiguration of trace hardware and
+         * disentangling of trace data per task.
+         */
+        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);
 }
 
 /*
@@ -701,8 +721,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
         /*
          * Now maybe reload the debug registers and handle I/O bitmaps
          */
-        if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
-            || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
+        if (unlikely(task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT ||
+                     task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
                 __switch_to_xtra(prev_p, next_p, tss);
 
         /* If the task has used fpu the last 5 timeslices, just do a full