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

Resend using different mail client

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, 13 insertions, 5 deletions

diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index f55c003f5b63..21ea22fda5fc 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -169,9 +169,14 @@ static void enable_step(struct task_struct *child, bool block)
          */
         if (enable_single_step(child) && block) {
                 set_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
-                write_debugctlmsr(child, DEBUGCTLMSR_BTF);
-        } else if (test_and_clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR)) {
-                write_debugctlmsr(child, 0);
+                write_debugctlmsr(child,
+                                  child->thread.debugctlmsr | DEBUGCTLMSR_BTF);
+        } else {
+            write_debugctlmsr(child,
+                              child->thread.debugctlmsr & ~TIF_DEBUGCTLMSR);
+
+            if (!child->thread.debugctlmsr)
+                    clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
         }
 }
 
@@ -190,8 +195,11 @@ void user_disable_single_step(struct task_struct *child)
         /*
          * Make sure block stepping (BTF) is disabled.
          */
-        if (test_and_clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR))
-                write_debugctlmsr(child, 0);
+        write_debugctlmsr(child,
+                          child->thread.debugctlmsr & ~TIF_DEBUGCTLMSR);
+
+        if (!child->thread.debugctlmsr)
+                clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
 
         /* Always clear TIF_SINGLESTEP... */
         clear_tsk_thread_flag(child, TIF_SINGLESTEP);