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, 18 insertions, 1 deletions

diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 5350763a2d03..2b9db9371060 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -614,11 +614,21 @@ __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_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);
+                wrmsr(MSR_IA32_DS_AREA, next->ds_area_msr, 0);
+        }
+
+        if (next->debugctlmsr != debugctl)
                 wrmsr(MSR_IA32_DEBUGCTLMSR, next->debugctlmsr, 0);
 
         if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
@@ -642,6 +652,13 @@ __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
         }
 #endif
 
+        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);
+
+
         if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
                 /*
                  * Disable the bitmap via an invalid offset. We still cache