[PATCH V2 8/8] powerpc: Add the ability to save VSX without giving it up

[Cyril Bur]

On Fri, 15 Jan 2016 17:25:26 +1100
Michael Neuling <mikey at neuling.org> wrote:

> On Fri, 2016-01-15 at 16:04 +1100, Cyril Bur wrote:
> > This patch adds the ability to be able to save the VSX registers to
> > the
> > thread struct without giving up (disabling the facility) next time
> > the
> > process returns to userspace.
> > 
> > This patch builds on a previous optimisation for the FPU and VEC
> > registers
> > in the thread copy path to avoid a possibly pointless reload of VSX
> > state.
> > 
> > Signed-off-by: Cyril Bur <cyrilbur at gmail.com>
> > ---
> >  arch/powerpc/include/asm/switch_to.h |  1 -
> >  arch/powerpc/kernel/ppc_ksyms.c      |  4 ----
> >  arch/powerpc/kernel/process.c        | 23 ++++++++++++++++++-----
> >  arch/powerpc/kernel/vector.S         | 17 -----------------
> >  4 files changed, 18 insertions(+), 27 deletions(-)
> > 
> > diff --git a/arch/powerpc/include/asm/switch_to.h
> > b/arch/powerpc/include/asm/switch_to.h
> > index 29dda9d..4dfcd3e 100644
> > --- a/arch/powerpc/include/asm/switch_to.h
> > +++ b/arch/powerpc/include/asm/switch_to.h
> > @@ -52,7 +52,6 @@ static inline void disable_kernel_altivec(void)
> >  extern void enable_kernel_vsx(void);
> >  extern void flush_vsx_to_thread(struct task_struct *);
> >  extern void giveup_vsx(struct task_struct *);
> > -extern void __giveup_vsx(struct task_struct *);
> >  static inline void disable_kernel_vsx(void)
> >  {
> >  	msr_check_and_clear(MSR_FP|MSR_VEC|MSR_VSX);
> > diff --git a/arch/powerpc/kernel/ppc_ksyms.c
> > b/arch/powerpc/kernel/ppc_ksyms.c
> > index 41e1607..ef7024da 100644
> > --- a/arch/powerpc/kernel/ppc_ksyms.c
> > +++ b/arch/powerpc/kernel/ppc_ksyms.c
> > @@ -28,10 +28,6 @@ EXPORT_SYMBOL(load_vr_state);
> >  EXPORT_SYMBOL(store_vr_state);
> >  #endif
> >  
> > -#ifdef CONFIG_VSX
> > -EXPORT_SYMBOL_GPL(__giveup_vsx);
> > -#endif
> > -
> >  #ifdef CONFIG_EPAPR_PARAVIRT
> >  EXPORT_SYMBOL(epapr_hypercall_start);
> >  #endif
> > diff --git a/arch/powerpc/kernel/process.c
> > b/arch/powerpc/kernel/process.c
> > index 5566c32..3d907b8 100644
> > --- a/arch/powerpc/kernel/process.c
> > +++ b/arch/powerpc/kernel/process.c
> > @@ -252,20 +252,33 @@ EXPORT_SYMBOL_GPL(flush_altivec_to_thread);
> >  #endif /* CONFIG_ALTIVEC */
> >  
> >  #ifdef CONFIG_VSX
> > -void giveup_vsx(struct task_struct *tsk)
> > +void __giveup_vsx(struct task_struct *tsk)
> >  {
> > -	check_if_tm_restore_required(tsk);
> > -
> > -	msr_check_and_set(MSR_FP|MSR_VEC|MSR_VSX);
> >  	if (tsk->thread.regs->msr & MSR_FP)
> >  		__giveup_fpu(tsk);
> >  	if (tsk->thread.regs->msr & MSR_VEC)
> >  		__giveup_altivec(tsk);
> > +	tsk->thread.regs->msr &= ~MSR_VSX;
> > +}
> > +
> > +void giveup_vsx(struct task_struct *tsk)
> > +{
> > +	check_if_tm_restore_required(tsk);
> > +
> > +	msr_check_and_set(MSR_FP|MSR_VEC|MSR_VSX);
> >  	__giveup_vsx(tsk);
> >  	msr_check_and_clear(MSR_FP|MSR_VEC|MSR_VSX);
> >  }
> >  EXPORT_SYMBOL(giveup_vsx);
> >  
> > +void save_vsx(struct task_struct *tsk)
> > +{
> > +	if (tsk->thread.regs->msr & MSR_FP)
> > +		save_fpu(tsk);
> > +	if (tsk->thread.regs->msr & MSR_VEC)
> > +		save_altivec(tsk);
> > +}
> > +
> >  void enable_kernel_vsx(void)
> >  {
> >  	WARN_ON(preemptible());
> > @@ -465,7 +478,7 @@ void save_all(struct task_struct *tsk)
> >  #endif
> >  #ifdef CONFIG_VSX
> >  	if (usermsr & MSR_VSX)
> > -		__giveup_vsx(tsk);
> > +		save_vsx(tsk);  
> 
> This seems suboptimal.  save_vsx() will call save_fpu() and
> save_altivec() again, which you just called earlier in save_all().
> 

Ah yes, will fix

> save_vsx() is only used here, so could be static. 
> 

Thanks.

> Also, put the #ifdef junk as part of the function so that the caller
> doesn't have to deal with it. 
> 

Can do absolutely, however this means that in save_all I can't check if the
function needs to be called or not. For example, without CONFIG_VSX, MSR_VSX
won't exist which means we might end up calling save_vsx THEN checking MSR_VSX
and returning early.

I'm happy to defer to you and mpe on what's nicer, I would side with avoiding
the function call at the cost of ugly #ifdefs but I can always see the merits
of clean code.

Thanks for the review,

Cyril

> Mikey
> 
> >  #endif
> >  #ifdef CONFIG_SPE
> >  	if (usermsr & MSR_SPE)
> > diff --git a/arch/powerpc/kernel/vector.S
> > b/arch/powerpc/kernel/vector.S
> > index 51b0c17..1c2e7a3 100644
> > --- a/arch/powerpc/kernel/vector.S
> > +++ b/arch/powerpc/kernel/vector.S
> > @@ -151,23 +151,6 @@ _GLOBAL(load_up_vsx)
> >  	std	r12,_MSR(r1)
> >  	b	fast_exception_return
> >  
> > -/*
> > - * __giveup_vsx(tsk)
> > - * Disable VSX for the task given as the argument.
> > - * Does NOT save vsx registers.
> > - */
> > -_GLOBAL(__giveup_vsx)
> > -	addi	r3,r3,THREAD		/* want THREAD of
> > task */
> > -	ld	r5,PT_REGS(r3)
> > -	cmpdi	0,r5,0
> > -	beq	1f
> > -	ld	r4,_MSR-STACK_FRAME_OVERHEAD(r5)
> > -	lis	r3,MSR_VSX at h
> > -	andc	r4,r4,r3		/* disable VSX for
> > previous task */
> > -	std	r4,_MSR-STACK_FRAME_OVERHEAD(r5)
> > -1:
> > -	blr
> > -
> >  #endif /* CONFIG_VSX */
> >  
> >