On Fri, 2016-01-15 at 16:04 +1100, Cyril Bur wrote:
> 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.
This comment seems misleading. The patch seems to touch the VSX, VMX
and SPE state as well.
Mikey
>
> Signed-off-by: Cyril Bur <cyril...@gmail.com>
> ---
> arch/powerpc/include/asm/switch_to.h | 2 +-
> arch/powerpc/kernel/fpu.S | 21 ++++------------
> arch/powerpc/kernel/process.c | 46
> +++++++++++++++++++++++++++++++++++-
> 3 files changed, 50 insertions(+), 19 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/switch_to.h
> b/arch/powerpc/include/asm/switch_to.h
> index 5b268b6..c4d50e9 100644
> --- a/arch/powerpc/include/asm/switch_to.h
> +++ b/arch/powerpc/include/asm/switch_to.h
> @@ -28,7 +28,7 @@ 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);
> diff --git a/arch/powerpc/kernel/fpu.S b/arch/powerpc/kernel/fpu.S
> index b063524..15da2b5 100644
> --- a/arch/powerpc/kernel/fpu.S
> +++ b/arch/powerpc/kernel/fpu.S
> @@ -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
>
> /*
> diff --git a/arch/powerpc/kernel/process.c
> b/arch/powerpc/kernel/process.c
> index ec53468..8a96e4f 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -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);
> @@ -421,12 +431,46 @@ void restore_math(struct pt_regs *regs)
> regs->msr = msr;
> }
>
> +void save_all(struct task_struct *tsk)
> +{
> + unsigned long usermsr;
> +
> + if (!tsk->thread.regs)
> + return;
> +
> + usermsr = tsk->thread.regs->msr;
> +
> + if ((usermsr & msr_all_available) == 0)
> + return;
> +
> + msr_check_and_set(msr_all_available);
> +
> +#ifdef CONFIG_PPC_FPU
> + if (usermsr & MSR_FP)
> + save_fpu(tsk);
> +#endif
> +#ifdef CONFIG_ALTIVEC
> + if (usermsr & MSR_VEC)
> + __giveup_altivec(tsk);
> +#endif
> +#ifdef CONFIG_VSX
> + if (usermsr & MSR_VSX)
> + __giveup_vsx(tsk);
> +#endif
> +#ifdef CONFIG_SPE
> + if (usermsr & MSR_SPE)
> + __giveup_spe(tsk);
> +#endif
> +
> + msr_check_and_clear(msr_all_available);
> +}
> +
> void flush_all_to_thread(struct task_struct *tsk)
> {
> if (tsk->thread.regs) {
> preempt_disable();
> BUG_ON(tsk != current);
> - giveup_all(tsk);
> + save_all(tsk);
>
> #ifdef CONFIG_SPE
> if (tsk->thread.regs->msr & MSR_SPE)
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