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Commit 8ed1383f authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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.
parent b339a18b

arch/i386/kernel/i387.c

+0 −11
Original line number Diff line number Diff line
@@ -82,17 +82,6 @@ void kernel_fpu_begin(void) 
}

EXPORT_SYMBOL_GPL(kernel_fpu_begin);



void restore_fpu( struct task_struct *tsk )

{

	if ( cpu_has_fxsr ) {

		asm volatile( "fxrstor %0"

			      : : "m" (tsk->thread.i387.fxsave) );

	} else {

		asm volatile( "frstor %0"

			      : : "m" (tsk->thread.i387.fsave) );

	}

}



/*

 * FPU tag word conversions.

 */

include/asm-i386/i387.h

+12 −1
Original line number Diff line number Diff line
@@ -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)