x86: debugctlmsr arch_has_block_step

This implements user-mode step-until-branch on x86 using the BTF bit
in MSR_IA32_DEBUGCTLMSR.  It's just like single-step, only less so.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/kernel/traps_64.c b/arch/x86/kernel/traps_64.c
index 874aca397b02..610a64d6bdf0 100644
--- a/arch/x86/kernel/traps_64.c
+++ b/arch/x86/kernel/traps_64.c
@@ -850,6 +850,12 @@ asmlinkage void __kprobes do_debug(struct pt_regs * regs,
 
         get_debugreg(condition, 6);
 
+        /*
+         * The processor cleared BTF, so don't mark that we need it set.
+         */
+        clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
+        tsk->thread.debugctlmsr = 0;
+
         if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
                                                 SIGTRAP) == NOTIFY_STOP)
                 return;