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Commit e6e9cac8 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge
Browse files

x86: split out core __math_state_restore 



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).

[ Impact: refactor code to make reuse cleaner; no functional change ]

Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Alok Kataria <akataria@vmware.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
parent 3fe0344f

arch/x86/include/asm/i387.h

+1 −0
Original line number Diff line number Diff line
@@ -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 *);

arch/x86/kernel/traps.c

+23 −10
Original line number Diff line number Diff line
@@ -813,6 +813,28 @@ asmlinkage void __attribute__((weak)) smp_threshold_interrupt(void) 
{

}



/*

 * __math_state_restore assumes that cr0.TS is already clear and the

 * fpu state is all ready for use.  Used during context switch.

 */

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);