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>

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);

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);

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  {							\

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)));

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.

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