Commit 8792468d authored by Cyril Bur's avatar Cyril Bur Committed by Michael Ellerman
Browse files

powerpc: Add the ability to save FPU without giving it up 



This patch adds the ability to be able to save the FPU registers to the
thread struct without giving up (disabling the facility) next time the
process returns to userspace.

This patch optimises the thread copy path (as a result of a fork() or
clone()) so that the parent thread can return to userspace with hot
registers avoiding a possibly pointless reload of FPU register state.

Signed-off-by: default avatarCyril Bur <cyrilbur@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent de2a20aa

arch/powerpc/include/asm/switch_to.h

+2 −1
Original line number Diff line number Diff line
@@ -28,13 +28,14 @@ extern void giveup_all(struct task_struct *); 
extern void enable_kernel_fp(void);

extern void flush_fp_to_thread(struct task_struct *);

extern void giveup_fpu(struct task_struct *);

extern void __giveup_fpu(struct task_struct *);

extern void save_fpu(struct task_struct *);

static inline void disable_kernel_fp(void)

{

	msr_check_and_clear(MSR_FP);

}

#else

static inline void __giveup_fpu(struct task_struct *t) { }

static inline void save_fpu(struct task_struct *t) { }

static inline void flush_fp_to_thread(struct task_struct *t) { }

#endif

arch/powerpc/kernel/fpu.S

+4 −17
Original line number Diff line number Diff line
@@ -143,33 +143,20 @@ END_FTR_SECTION_IFSET(CPU_FTR_VSX) 
	blr



/*

 * __giveup_fpu(tsk)

 * Disable FP for the task given as the argument,

 * and save the floating-point registers in its thread_struct.

 * save_fpu(tsk)

 * Save the floating-point registers in its thread_struct.

 * Enables the FPU for use in the kernel on return.

 */

_GLOBAL(__giveup_fpu)

_GLOBAL(save_fpu)

	addi	r3,r3,THREAD	        /* want THREAD of task */

	PPC_LL	r6,THREAD_FPSAVEAREA(r3)

	PPC_LL	r5,PT_REGS(r3)

	PPC_LCMPI	0,r6,0

	bne	2f

	addi	r6,r3,THREAD_FPSTATE

2:	PPC_LCMPI	0,r5,0

	SAVE_32FPVSRS(0, R4, R6)

2:	SAVE_32FPVSRS(0, R4, R6)

	mffs	fr0

	stfd	fr0,FPSTATE_FPSCR(r6)

	beq	1f

	PPC_LL	r4,_MSR-STACK_FRAME_OVERHEAD(r5)

	li	r3,MSR_FP|MSR_FE0|MSR_FE1

#ifdef CONFIG_VSX

BEGIN_FTR_SECTION

	oris	r3,r3,MSR_VSX@h

END_FTR_SECTION_IFSET(CPU_FTR_VSX)

#endif

	andc	r4,r4,r3		/* disable FP for previous task */

	PPC_STL	r4,_MSR-STACK_FRAME_OVERHEAD(r5)

1:

	blr



/*

arch/powerpc/kernel/process.c

+11 −1
Original line number Diff line number Diff line
@@ -133,6 +133,16 @@ void __msr_check_and_clear(unsigned long bits) 
EXPORT_SYMBOL(__msr_check_and_clear);



#ifdef CONFIG_PPC_FPU

void __giveup_fpu(struct task_struct *tsk)

{

	save_fpu(tsk);

	tsk->thread.regs->msr &= ~MSR_FP;

#ifdef CONFIG_VSX

	if (cpu_has_feature(CPU_FTR_VSX))

		tsk->thread.regs->msr &= ~MSR_VSX;

#endif

}



void giveup_fpu(struct task_struct *tsk)

{

	check_if_tm_restore_required(tsk);
@@ -459,7 +469,7 @@ void save_all(struct task_struct *tsk) 
	msr_check_and_set(msr_all_available);



	if (usermsr & MSR_FP)

		__giveup_fpu(tsk);

		save_fpu(tsk);



	if (usermsr & MSR_VEC)

		__giveup_altivec(tsk);

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