i387: re-introduce FPU state preloading at context switch time

[pandora-kernel.git] / arch / x86 / kernel / traps.c

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index ad25e51..77da5b4 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -570,6 +570,37 @@ asmlinkage void __attribute__((weak)) smp_threshold_interrupt(void)
 {
 }
 
+/*
+ * This gets called with the process already owning the
+ * FPU state, and with CR0.TS cleared. It just needs to
+ * restore the FPU register state.
+ */
+void __math_state_restore(struct task_struct *tsk)
+{
+       /* We need a safe address that is cheap to find and that is already
+          in L1. We've just brought in "tsk->thread.has_fpu", so use that */
+#define safe_address (tsk->thread.has_fpu)
+
+       /* AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception
+          is pending.  Clear the x87 state here by setting it to fixed
+          values. safe_address is a random variable that should be in L1 */
+       alternative_input(
+               ASM_NOP8 ASM_NOP2,
+               "emms\n\t"              /* clear stack tags */
+               "fildl %P[addr]",       /* set F?P to defined value */
+               X86_FEATURE_FXSAVE_LEAK,
+               [addr] "m" (safe_address));
+
+       /*
+        * Paranoid restore. send a SIGSEGV if we fail to restore the state.
+        */
+       if (unlikely(restore_fpu_checking(tsk))) {
+               __thread_fpu_end(tsk);
+               force_sig(SIGSEGV, tsk);
+               return;
+       }
+}
+
 /*
  * 'math_state_restore()' saves the current math information in the
  * old math state array, and gets the new ones from the current task
@@ -584,10 +615,6 @@ void math_state_restore(void)
 {
        struct task_struct *tsk = current;
 
-       /* We need a safe address that is cheap to find and that is already
-          in L1. We're just bringing in "tsk->thread.has_fpu", so use that */
-#define safe_address (tsk->thread.has_fpu)
-
        if (!tsk_used_math(tsk)) {
                local_irq_enable();
                /*
@@ -604,25 +631,7 @@ void math_state_restore(void)
        }
 
        __thread_fpu_begin(tsk);
-
-       /* AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception
-          is pending.  Clear the x87 state here by setting it to fixed
-          values. safe_address is a random variable that should be in L1 */
-       alternative_input(
-               ASM_NOP8 ASM_NOP2,
-               "emms\n\t"              /* clear stack tags */
-               "fildl %P[addr]",       /* set F?P to defined value */
-               X86_FEATURE_FXSAVE_LEAK,
-               [addr] "m" (safe_address));
-
-       /*
-        * Paranoid restore. send a SIGSEGV if we fail to restore the state.
-        */
-       if (unlikely(restore_fpu_checking(tsk))) {
-               __thread_fpu_end(tsk);
-               force_sig(SIGSEGV, tsk);
-               return;
-       }
+       __math_state_restore(tsk);
 
        tsk->fpu_counter++;
 }