[PATCH v2 4/4] powerpc/tm: Do not recheckpoint non-tm task

[Michael Neuling]

On Mon, 2018-06-18 at 19:59 -0300, Breno Leitao wrote:
> If __switch_to() tries to context switch from task A to task B, and task A
>  had task->thread->regs->msr[TM] enabled, then __switch_to_tm() will call
> tm_recheckpoint_new_task(), which will call trecheckpoint, for task B, which
>  is clearly wrong since task B might not be an active TM user.
> 
> This does not cause a lot of damage because tm_recheckpoint() will abort
> the call since it realize that the current task does not have msr[TM] bit
> set.
> 
> Signed-off-by: Breno Leitao <leitao at debian.org>
> ---
>  arch/powerpc/kernel/process.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index f8beee03f00a..d26a150766ef 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -1036,7 +1036,8 @@ static inline void __switch_to_tm(struct task_struct
> *prev,
>  				prev->thread.regs->msr &= ~MSR_TM;
>  		}
>  
> -		tm_recheckpoint_new_task(new);
> +		if (tm_enabled(new))
> +			tm_recheckpoint_new_task(new);

I'm not sure we need this patch as tm_recheckpoint_new_task() does this itself.

---
static inline void tm_recheckpoint_new_task(struct task_struct *new)
{
	if (!cpu_has_feature(CPU_FTR_TM))
		return;

	/* Recheckpoint the registers of the thread we're about to switch to.
	 *
	 * If the task was using FP, we non-lazily reload both the original and
	 * the speculative FP register states.  This is because the kernel
	 * doesn't see if/when a TM rollback occurs, so if we take an FP
	 * unavailable later, we are unable to determine which set of FP regs
	 * need to be restored.
	 */
	if (!tm_enabled(new))
		return;


---
Mikey