x86, perf, bts, mm: Delete the never used BTS-ptrace code

Support for the PMU's BTS features has been upstreamed in
v2.6.32, but we still have the old and disabled ptrace-BTS,
as Linus noticed it not so long ago.

It's buggy: TIF_DEBUGCTLMSR is trampling all over that MSR without
regard for other uses (perf) and doesn't provide the flexibility
needed for perf either.

Its users are ptrace-block-step and ptrace-bts, since ptrace-bts
was never used and ptrace-block-step can be implemented using a
much simpler approach.

So axe all 3000 lines of it. That includes the *locked_memory*()
APIs in mm/mlock.c as well.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Markus Metzger <markus.t.metzger@intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <20100325135413.938004390@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 32 deletions

diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 3149032ff107..7beba0769a8c 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -158,22 +158,6 @@ static int enable_single_step(struct task_struct *child)
 }
 
 /*
- * Install this value in MSR_IA32_DEBUGCTLMSR whenever child is running.
- */
-static void write_debugctlmsr(struct task_struct *child, unsigned long val)
-{
-        if (child->thread.debugctlmsr == val)
-                return;
-
-        child->thread.debugctlmsr = val;
-
-        if (child != current)
-                return;
-
-        update_debugctlmsr(val);
-}
-
-/*
  * Enable single or block step.
  */
 static void enable_step(struct task_struct *child, bool block)
@@ -185,17 +169,9 @@ static void enable_step(struct task_struct *child, bool block)
          * So noone should try to use debugger block stepping in a program
          * that uses user-mode single stepping itself.
          */
-        if (enable_single_step(child) && block) {
-                set_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
-                write_debugctlmsr(child,
-                                  child->thread.debugctlmsr | DEBUGCTLMSR_BTF);
-        } else {
-                write_debugctlmsr(child,
-                                  child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF);
-
-                if (!child->thread.debugctlmsr)
-                        clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
-        }
+        if (!enable_single_step(child))
+                return;
+        /* XXX */
 }
 
 void user_enable_single_step(struct task_struct *child)
@@ -213,11 +189,7 @@ void user_disable_single_step(struct task_struct *child)
         /*
          * Make sure block stepping (BTF) is disabled.
          */
-        write_debugctlmsr(child,
-                          child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF);
-
-        if (!child->thread.debugctlmsr)
-                clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
+        /* XXX */
 
         /* Always clear TIF_SINGLESTEP... */
         clear_tsk_thread_flag(child, TIF_SINGLESTEP);