x86: fix taking DNA during 64bit sigreturn

restore sigcontext is taking a DNA exception while restoring FP context
from the user stack, during the sigreturn.  Appended patch fixes it by
doing clts() if the app doesn't touch FP during the signal handler
execution.  This will stop generating a DNA, during the fxrstor in the
sigreturn.

This improves 64-bit lat_sig numbers by ~30% on my core2 platform.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/x86/kernel/i387_64.c b/arch/x86/kernel/i387_64.c
index 56c1f11471099103292b5aa291a388113d27fa9b..bfaff28fb1348f41f14b7caadf363ca86879595e 100644 (file)
--- a/arch/x86/kernel/i387_64.c
+++ b/arch/x86/kernel/i387_64.c
@@ -92,13 +92,14 @@ int save_i387(struct _fpstate __user *buf)
        if (task_thread_info(tsk)->status & TS_USEDFPU) {
                err = save_i387_checking((struct i387_fxsave_struct __user *)buf);
                if (err) return err;
+               task_thread_info(tsk)->status &= ~TS_USEDFPU;
                stts();
-               } else {
-               if (__copy_to_user(buf, &tsk->thread.i387.fxsave, 
+       } else {
+               if (__copy_to_user(buf, &tsk->thread.i387.fxsave,
                                   sizeof(struct i387_fxsave_struct)))
                        return -1;
-       } 
-               return 1;
+       }
+       return 1;
 }
 
 /*

diff --git a/include/asm-x86/i387_64.h b/include/asm-x86/i387_64.h
index 0217b74cc9fc0cd30456d40929e6196229680178..3a4ffba3d6bcf2c30bbad9e6cd7f87cce8a165ba 100644 (file)
--- a/include/asm-x86/i387_64.h
+++ b/include/asm-x86/i387_64.h
@@ -203,6 +203,11 @@ static inline void save_init_fpu(struct task_struct *tsk)
  */
 static inline int restore_i387(struct _fpstate __user *buf)
 {
+       set_used_math();
+       if (!(task_thread_info(current)->status & TS_USEDFPU)) {
+               clts();
+               task_thread_info(current)->status |= TS_USEDFPU;
+       }
        return restore_fpu_checking((__force struct i387_fxsave_struct *)buf);
 }