x86: make restore_fpu() use alternative assembler instructions

It's really just a single instruction, conditional on whether the CPU
supports FXSR or not, so implement it as such instead of making it a
function that queries FXSR dynamically.

This means that the instruction just gets automatically rewritten to the
correct one at boot-time.

1 files changed, 12 insertions, 1 deletions

diff --git a/include/asm-i386/i387.h b/include/asm-i386/i387.h
index f6feb98a9397..e678609bb57e 100644
--- a/include/asm-i386/i387.h
+++ b/include/asm-i386/i387.h
@@ -19,10 +19,21 @@
 
 extern void mxcsr_feature_mask_init(void);
 extern void init_fpu(struct task_struct *);
+
 /*
  * FPU lazy state save handling...
  */
-extern void restore_fpu( struct task_struct *tsk );
+
+/*
+ * The "nop" is needed to make the instructions the same
+ * length.
+ */
+#define restore_fpu(tsk)                        \
+        alternative_input(                      \
+                "nop ; frstor %1",              \
+                "fxrstor %1",                   \
+                X86_FEATURE_FXSR,               \
+                "m" ((tsk)->thread.i387.fsave))
 
 extern void kernel_fpu_begin(void);
 #define kernel_fpu_end() do { stts(); preempt_enable(); } while(0)