[RFC PATCH 08/11] powerpc/tm: Do not reclaim on ptrace

[Michael Neuling]

On Wed, 2018-09-12 at 16:40 -0300, Breno Leitao wrote:
> Make sure that we are not suspended on ptrace and that the registers were
> already reclaimed.
> 
> Since the data was already reclaimed, there is nothing to be done here
> except to restore the SPRs.
> 
> Signed-off-by: Breno Leitao <leitao at debian.org>
> ---
>  arch/powerpc/kernel/ptrace.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index 9667666eb18e..cf6ee9154b11 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -136,12 +136,10 @@ static void flush_tmregs_to_thread(struct task_struct
> *tsk)
>  	if ((!cpu_has_feature(CPU_FTR_TM)) || (tsk != current))
>  		return;
>  
> -	if (MSR_TM_SUSPENDED(mfmsr())) {
> -		tm_reclaim_current(TM_CAUSE_SIGNAL);
> -	} else {
> -		tm_enable();
> -		tm_save_sprs(&(tsk->thread));
> -	}
> +	WARN_ON(MSR_TM_SUSPENDED(mfmsr()));
> +
> +	tm_enable();
> +	tm_save_sprs(&(tsk->thread));

Do we need to check if TM was enabled in the task before saving the TM SPRs?

What happens if TM was lazily off and hence we had someone else's TM SPRs in the
CPU currently?  Wouldn't this flush the wrong values to the task_struct?

I think we need to check the processes MSR before doing this.

Mikey

>  }
>  #else
>  static inline void flush_tmregs_to_thread(struct task_struct *tsk) { }