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>

6 files changed, 19 insertions, 4 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);
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index f7356e5517f6..ae5eca17aa3c 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -555,6 +555,9 @@ static inline void __switch_to_xtra(struct task_struct *prev_p,
         prev = &prev_p->thread,
         next = &next_p->thread;
 
+        if (next->debugctlmsr != prev->debugctlmsr)
+                wrmsrl(MSR_IA32_DEBUGCTLMSR, next->debugctlmsr);
+
         if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
                 loaddebug(next, 0);
                 loaddebug(next, 1);
diff --git a/include/asm-x86/processor_32.h b/include/asm-x86/processor_32.h
index 2540bf8d5724..3c67eacb3168 100644
--- a/include/asm-x86/processor_32.h
+++ b/include/asm-x86/processor_32.h
@@ -368,6 +368,8 @@ struct thread_struct {
         unsigned long   iopl;
 /* max allowed port in the bitmap, in bytes: */
         unsigned long   io_bitmap_max;
+/* MSR_IA32_DEBUGCTLMSR value to switch in if TIF_DEBUGCTLMSR is set.  */
+        unsigned long   debugctlmsr;
 };
 
 #define INIT_THREAD  {                                                  \
diff --git a/include/asm-x86/processor_64.h b/include/asm-x86/processor_64.h
index 20d8935d141a..e7bea4fed642 100644
--- a/include/asm-x86/processor_64.h
+++ b/include/asm-x86/processor_64.h
@@ -238,6 +238,8 @@ struct thread_struct {
         int             ioperm;
         unsigned long   *io_bitmap_ptr;
         unsigned io_bitmap_max;
+/* MSR_IA32_DEBUGCTLMSR value to switch in if TIF_DEBUGCTLMSR is set.  */
+        unsigned long   debugctlmsr;
 /* cached TLS descriptors. */
         u64 tls_array[GDT_ENTRY_TLS_ENTRIES];
 } __attribute__((aligned(16)));
diff --git a/include/asm-x86/thread_info_32.h b/include/asm-x86/thread_info_32.h
index 009ecc6ad38b..306fc80800e1 100644
--- a/include/asm-x86/thread_info_32.h
+++ b/include/asm-x86/thread_info_32.h
@@ -139,6 +139,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_FREEZE              19      /* is freezing for suspend */
 #define TIF_NOTSC               20      /* TSC is not accessible in userland */
 #define TIF_FORCED_TF           21      /* true if TF in eflags artificially */
+#define TIF_DEBUGCTLMSR         22      /* uses thread_struct.debugctlmsr */
 
 #define _TIF_SYSCALL_TRACE      (1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING         (1<<TIF_SIGPENDING)
@@ -155,6 +156,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_FREEZE             (1<<TIF_FREEZE)
 #define _TIF_NOTSC              (1<<TIF_NOTSC)
 #define _TIF_FORCED_TF          (1<<TIF_FORCED_TF)
+#define _TIF_DEBUGCTLMSR        (1<<TIF_DEBUGCTLMSR)
 
 /* work to do on interrupt/exception return */
 #define _TIF_WORK_MASK \
@@ -164,8 +166,8 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_ALLWORK_MASK       (0x0000FFFF & ~_TIF_SECCOMP)
 
 /* flags to check in __switch_to() */
-#define _TIF_WORK_CTXSW_NEXT (_TIF_IO_BITMAP | _TIF_NOTSC | _TIF_DEBUG)
-#define _TIF_WORK_CTXSW_PREV (_TIF_IO_BITMAP | _TIF_NOTSC)
+#define _TIF_WORK_CTXSW_NEXT (_TIF_IO_BITMAP | _TIF_NOTSC | _TIF_DEBUG | _TIF_DEBUGCTLMSR)
+#define _TIF_WORK_CTXSW_PREV (_TIF_IO_BITMAP | _TIF_NOTSC | _TIF_DEBUGCTLMSR)
 
 /*
  * Thread-synchronous status.
diff --git a/include/asm-x86/thread_info_64.h b/include/asm-x86/thread_info_64.h
index e0f41b3deced..ee35fd12b541 100644
--- a/include/asm-x86/thread_info_64.h
+++ b/include/asm-x86/thread_info_64.h
@@ -122,6 +122,7 @@ static inline struct thread_info *stack_thread_info(void)
 #define TIF_IO_BITMAP           22      /* uses I/O bitmap */
 #define TIF_FREEZE              23      /* is freezing for suspend */
 #define TIF_FORCED_TF           24      /* true if TF in eflags artificially */
+#define TIF_DEBUGCTLMSR         25      /* uses thread_struct.debugctlmsr */
 
 #define _TIF_SYSCALL_TRACE      (1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING         (1<<TIF_SIGPENDING)
@@ -140,6 +141,7 @@ static inline struct thread_info *stack_thread_info(void)
 #define _TIF_IO_BITMAP          (1<<TIF_IO_BITMAP)
 #define _TIF_FREEZE             (1<<TIF_FREEZE)
 #define _TIF_FORCED_TF          (1<<TIF_FORCED_TF)
+#define _TIF_DEBUGCTLMSR        (1<<TIF_DEBUGCTLMSR)
 
 /* work to do on interrupt/exception return */
 #define _TIF_WORK_MASK \
@@ -151,7 +153,7 @@ static inline struct thread_info *stack_thread_info(void)
         (_TIF_SIGPENDING|_TIF_SINGLESTEP|_TIF_MCE_NOTIFY|_TIF_HRTICK_RESCHED)
 
 /* flags to check in __switch_to() */
-#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP)
+#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP|_TIF_DEBUGCTLMSR)
 
 #define PREEMPT_ACTIVE     0x10000000