x86: debugctlmsr context switch

This adds low-level support for a per-thread value of MSR_IA32_DEBUGCTLMSR.
The per-thread value is switched in when TIF_DEBUGCTLMSR is set.

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, 5 insertions, 1 deletions

diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index d9905c9d0fd5..d5462f228daf 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -602,10 +602,14 @@ static noinline void
 __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
                  struct tss_struct *tss)
 {
-        struct thread_struct *next;
+        struct thread_struct *prev, *next;
 
+        prev = &prev_p->thread;
         next = &next_p->thread;
 
+        if (next->debugctlmsr != prev->debugctlmsr)
+                wrmsr(MSR_IA32_DEBUGCTLMSR, next->debugctlmsr, 0);
+
         if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
                 set_debugreg(next->debugreg[0], 0);
                 set_debugreg(next->debugreg[1], 1);