x86: Eliminate TS_XSAVE

The fpu code currently uses current->thread_info->status & TS_XSAVE as
a way to distinguish between XSAVE capable processors and older processors.
The decision is not really task specific; instead we use the task status to
avoid a global memory reference - the value should be the same across all
threads.

Eliminate this tie-in into the task structure by using an alternative
instruction keyed off the XSAVE cpu feature; this results in shorter and
faster code, without introducing a global memory reference.

[ hpa: in the future, this probably should use an asm jmp ]

Signed-off-by: Avi Kivity <avi@redhat.com>
Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <1273135546-29690-2-git-send-email-avi@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

5 files changed, 21 insertions, 16 deletions

diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index da293092450..a301a6825c3 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -56,6 +56,18 @@ extern int restore_i387_xstate_ia32(void __user *buf);
 
 #define X87_FSW_ES (1 << 7)     /* Exception Summary */
 
+static inline bool use_xsave(void)
+{
+        u8 has_xsave;
+
+        alternative_io("mov $0, %0",
+                       "mov $1, %0",
+                       X86_FEATURE_XSAVE,
+                       "=g"(has_xsave));
+
+        return has_xsave;
+}
+
 #ifdef CONFIG_X86_64
 
 /* Ignore delayed exceptions from user space */
@@ -99,7 +111,7 @@ static inline void clear_fpu_state(struct task_struct *tsk)
         /*
          * xsave header may indicate the init state of the FP.
          */
-        if ((task_thread_info(tsk)->status & TS_XSAVE) &&
+        if (use_xsave() &&
             !(xstate->xsave_hdr.xstate_bv & XSTATE_FP))
                 return;
 
@@ -164,7 +176,7 @@ static inline void fxsave(struct task_struct *tsk)
 
 static inline void __save_init_fpu(struct task_struct *tsk)
 {
-        if (task_thread_info(tsk)->status & TS_XSAVE)
+        if (use_xsave())
                 xsave(tsk);
         else
                 fxsave(tsk);
@@ -218,7 +230,7 @@ static inline int fxrstor_checking(struct i387_fxsave_struct *fx)
  */
 static inline void __save_init_fpu(struct task_struct *tsk)
 {
-        if (task_thread_info(tsk)->status & TS_XSAVE) {
+        if (use_xsave()) {
                 struct xsave_struct *xstate = &tsk->thread.xstate->xsave;
                 struct i387_fxsave_struct *fx = &tsk->thread.xstate->fxsave;
 
@@ -266,7 +278,7 @@ end:
 
 static inline int restore_fpu_checking(struct task_struct *tsk)
 {
-        if (task_thread_info(tsk)->status & TS_XSAVE)
+        if (use_xsave())
                 return xrstor_checking(&tsk->thread.xstate->xsave);
         else
                 return fxrstor_checking(&tsk->thread.xstate->fxsave);
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index e0d28901e96..e9e341505ab 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -244,7 +244,6 @@ static inline struct thread_info *current_thread_info(void)
 #define TS_POLLING              0x0004  /* true if in idle loop
                                            and not sleeping */
 #define TS_RESTORE_SIGMASK      0x0008  /* restore signal mask in do_signal() */
-#define TS_XSAVE                0x0010  /* Use xsave/xrstor */
 
 #define tsk_is_polling(t) (task_thread_info(t)->status & TS_POLLING)
 
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 4868e4a951e..c1c00d0b169 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1243,10 +1243,7 @@ void __cpuinit cpu_init(void)
         /*
          * Force FPU initialization:
          */
-        if (cpu_has_xsave)
-                current_thread_info()->status = TS_XSAVE;
-        else
-                current_thread_info()->status = 0;
+        current_thread_info()->status = 0;
         clear_used_math();
         mxcsr_feature_mask_init();
 
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 54c31c28548..14ca1dc7a70 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -102,10 +102,7 @@ void __cpuinit fpu_init(void)
 
         mxcsr_feature_mask_init();
         /* clean state in init */
-        if (cpu_has_xsave)
-                current_thread_info()->status = TS_XSAVE;
-        else
-                current_thread_info()->status = 0;
+        current_thread_info()->status = 0;
         clear_used_math();
 }
 #endif  /* CONFIG_X86_64 */
diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index 782c3a362ec..c1b0a11033a 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -99,7 +99,7 @@ int save_i387_xstate(void __user *buf)
                 if (err)
                         return err;
 
-                if (task_thread_info(tsk)->status & TS_XSAVE)
+                if (use_xsave())
                         err = xsave_user(buf);
                 else
                         err = fxsave_user(buf);
@@ -116,7 +116,7 @@ int save_i387_xstate(void __user *buf)
 
         clear_used_math(); /* trigger finit */
 
-        if (task_thread_info(tsk)->status & TS_XSAVE) {
+        if (use_xsave()) {
                 struct _fpstate __user *fx = buf;
                 struct _xstate __user *x = buf;
                 u64 xstate_bv;
@@ -225,7 +225,7 @@ int restore_i387_xstate(void __user *buf)
                 clts();
                 task_thread_info(current)->status |= TS_USEDFPU;
         }
-        if (task_thread_info(tsk)->status & TS_XSAVE)
+        if (use_xsave())
                 err = restore_user_xstate(buf);
         else
                 err = fxrstor_checking((__force struct i387_fxsave_struct *)