[Xen-devel] [PATCH 2/5] x86: split out core __math_state_restore

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

Split the core fpu state restoration out into __math_state_restore, which
assumes that cr0.TS is clear and that the fpu context has been initialized.

This will be used during context switch.  There are two reasons this is
desireable:

- There's a small clarification.  When __switch_to() calls math_state_restore,
  it relies on the fact that tsk_used_math() returns true, and so will
  never do a blocking init_fpu().  __math_state_restore() does not have
  (or need) that logic, so the question never arises.

- It allows the clts() to be moved earler in __switch_to() so it can be 
performed
  while cpu context updates are batched (will be done in a later patch).

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 arch/x86/include/asm/i387.h |    1 +
 arch/x86/kernel/traps.c     |   33 +++++++++++++++++++++++----------
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index 63d1850..6eda5d2 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -26,6 +26,7 @@ extern void fpu_init(void);
 extern void mxcsr_feature_mask_init(void);
 extern int init_fpu(struct task_struct *child);
 extern asmlinkage void math_state_restore(void);
+extern void __math_state_restore(void);
 extern void init_thread_xstate(void);
 extern int dump_fpu(struct pt_regs *, struct user_i387_struct *);
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index f07ada4..4ea50f7 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -814,6 +814,28 @@ asmlinkage void __attribute__((weak)) 
mce_threshold_interrupt(void)
 #endif
 
 /*
+ * __math_state_restore assumes that cr0.TS is already clear and the
+ * fpu state is all ready for use.  Used during context switch.
+ */
+inline void __math_state_restore(void)
+{
+       struct thread_info *thread = current_thread_info();
+       struct task_struct *tsk = thread->task;
+
+       /*
+        * Paranoid restore. send a SIGSEGV if we fail to restore the state.
+        */
+       if (unlikely(restore_fpu_checking(tsk))) {
+               stts();
+               force_sig(SIGSEGV, tsk);
+               return;
+       }
+
+       thread->status |= TS_USEDFPU;   /* So we fnsave on switch_to() */
+       tsk->fpu_counter++;
+}
+
+/*
  * 'math_state_restore()' saves the current math information in the
  * old math state array, and gets the new ones from the current task
  *
@@ -844,17 +866,8 @@ asmlinkage void math_state_restore(void)
        }
 
        clts();                         /* Allow maths ops (or we recurse) */
-       /*
-        * Paranoid restore. send a SIGSEGV if we fail to restore the state.
-        */
-       if (unlikely(restore_fpu_checking(tsk))) {
-               stts();
-               force_sig(SIGSEGV, tsk);
-               return;
-       }
 
-       thread->status |= TS_USEDFPU;   /* So we fnsave on switch_to() */
-       tsk->fpu_counter++;
+       __math_state_restore();
 }
 EXPORT_SYMBOL_GPL(math_state_restore);
 
-- 
1.6.0.6


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